International conference on
Quantum Optics 2016
Obergurgl, Tirol, Austria
February 21-27, 2016
Book of Abstracts
Chair:
Hanns-Christoph Nägerl (University of Innsbruck)
Co-chairs:
Helmut Ritsch (University of Innsbruck)
Jörg Schmiedmayer (TU Vienna)
Contents
Conference Schedule
Talks
Monday, February 22 . .
Tuesday, February 23 . .
Wednesday, February 24
Thursday, February 25 .
Friday, February 26 . . .
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5
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11
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31
Posters
37
Sponsors
83
Index
85
Conference Schedule
Conference Schedule
3
Talks
Talks
Monday, February 22
Invited Talk
Measurements not bounded by the Heisenberg uncertainty
principle
Eugene Polzik
Niels Bohr Institute, University of Copenhagen
Blegdamsvej 17, 2100 Copenhagen, Denmark
polzik@nbi.dk
Measurements of one quadrature of an oscillator with precision beyond its
vacuum state uncertainty have occupied a central place in quantum physics
for decades. We have recently reported the first experimental implementation
of such measurement with a magnetic oscillator [1]. However, a much more
intriguing goal is to trace an oscillator trajectory with the precision beyond
the vacuum state uncertainty in both position and momentum, a feat naively
assumed not possible due to the Heisenberg uncertainty principle. We have
demonstrated that such measurement is possible if the oscillator is entangled
with a quantum reference oscillator characterized by an effective negative
mass [2,3]. Progress towards such a measurement involving a macroscopic
mechanical oscillator will be reported. The key element is the cancellation of
the back action of the measurement on the composite system of two oscillators. Applications include measurements of e.-m. fields, accelleration, force
and time [4] with practically unlimited accuracy. In a more general sense, this
approach leads to trajectories without quantum uncertainties and to achieving new fundamental bounds on the measurement precision.
[1] Generation of a squeezed state of an oscillator by stroboscopic back-actionevading measurement. G. Vasilakis, H. Shen, K. Jensen, M. Balabas, D.
Salart, B. Chen, and E. S. Polzik. NaturePhysics, (2015)
doi:10.1038/nphys3280.
[2] Establishing Einstein-Podolsky-Rosen channels between nanomechanics
and atomic ensembles. K. Hammerer, M. Aspelmeyer, E.S. Polzik, P. Zoller.
Phys. Rev. Lett. 102, 020501 (2009).
[3] Trajectories without quantum uncertainties. E.S. Polzik and K.Hammerer.
Annalen der Physyk. 527, No. 1–2, A15–A20 (2015).
[4] Entanglement and spin-squeezing in a network of optical lattice clocks. E.
S. Polzik and J. Ye. arXiv:1508.02540
5
Talks
Invited Talk
Hybrid Quantum Processing with Cavity Photons and Single
Atoms
Axel Kuhn
University of Oxford
Clarendon Laboratory, OX1 3PU Oxford, UK
axel.kuhn@physics.ox.ac.uk
Cavity-mediated interfacing of stationary with flying quantum bits in the
form of atoms and photons is combined with on-chip linear optics quantum
computing to an hitherto unprecedented approach to quantum networking.
This hybrid scheme operates on-chip photonic quantum gates and entangling
operations with photons delivered on demand from a non-probabilistic atomphoton interface. Non-classical correlations are observed between events separated by periods exceeding the travel time across the chip by three orders of
magnitude. This paves the way to novel quantum technologies that exploit
both narrowband cavity photons and integrated quantum photonics, such as
scalable photonic quantum computing and narrow linewidth atomic memories.
6
Talks
Overlapping a Cs Mott insulator with superfluid Rb at tunable
interspecies interactions
Andreas Schindewolf
University Innsbruck
Technikerstraße 25/4, 6020 Innsbruck, Austria
andreas.schindewolf@uibk.ac.at
Ultracold dipolar systems are of high interest for quantum chemistry, precision spectroscopy, quantum many-body physics, and quantum simulation.
The goal of our project is to prepare an ultracold sample of dipolar RbCs
ground-state molecules in an optical lattice with a high filling factor. To this
end, atomic Rb and Cs samples are mixed in an optical lattice to efficiently
form Rb-Cs atom pairs as precursors to ground-state molecules. The basic
idea is to go through the superfluid-to-Mott-insulator phase transition twice,
first for Cs to create a sample with single-site occupancy, then for Rb on top
of Cs to create a homogenous distribution of atom pairs.
We investigate the transport properties of superfluid Rb samples while they
are moved on top of a strongly interacting sample of Cs atoms. Overlapping
is realized in the vicinity of a Feshbach-resonance zero crossing to tune the
interspecies interactions. We find a breakdown of the superfluid current for
sufficiently strong attractive interspecies interactions. For even stronger attractive interactions the samples are immiscible and superfluidity is restored.
Our experiments show that atom-pair formation is optimized for nulled interactions. We estimate the filling fraction to be 30% in the center of our
trap.
7
Talks
Invited Talk
Many-body localization and symmetry protected topology
Norman Yao
UC Berkeley
510 Beloit Ave., 94708 Kensington, USA
norman.yao@berkeley.edu
Owing to their natural isolation, quantum optical systems of atoms, ions and
molecules offer an attractive platform to study out-of-equilibrium quantum
dynamics and localization. Recent progress on many-body localized phases
has demonstrated that they can exhibit symmetry breaking and/or topological orders in dimensions normally forbidden by Mermin-Wagner arguments.
In this talk, I will describe how to coherently prepare, protect and detect
symmetry protected topological order in a non-equilibrium setting. I will
explore a 1D transverse-field Ising model with periodically driven two-body
terms whose Floquet dynamics mirror those of the celebrated Haldane phase.
Even in the presence of generic interactions, I will show that disorder leading to many-body localization prevents arbitrary heating of the system and
leads to an exponential enhancement of the edge spin coherence at infinite
temperature. Finally, I will describe a natural realization in a Rydberg ensemble, leveraging the blockade to controllably toggle between ferromagnetic
and antiferromagnetic Ising interactions.
Far-Field Optical Nanoscopy with Ultrashort Pulses
Oriol Romero-Isart
IQOQI and UNI Innsbruck
IQOQI Technikerstraße 21a, 6020 Innsbruck, Austria
oriol.romero-isart@uibk.ac.at
The Abbe diffraction limit applies to monochromatic light. Here we address
whether polychromatic light can be used for far-field optical microscopy. We
show that an ultrashort pulse can be focused to a spot size smaller than the
optical wavelength and can be used for far-field optical nanoscopy.
8
Talks
Invited Talk
Coherent Orbital Manipulation of SU(N) Fermi gases
Jacopo Catani
LENS and INO-CNR
via Nello Carrara, 1, I-50019 Sesto Fiorentino, Italy
catani@lens.unifi.it
In this talk I will report on recent results obtained in a SU(N) quantum degenerate Fermi gas of Yb by exploiting its orbital degree of freedom . Firstly,
I report on the evidence of inter-orbital coherent spin-exchange dynamics
achieved by a coherent manipulation of the orbital degree of freedom, exploiting the ultranarrow clock transition of 173Y b. Secondly, I will show how
the orbital degree of freedom can be efficiently employed in order to achieve
magnetic tunability of interactions in this non-magnetic atom. A new kind
of Feshbach resonance (orbital Feshbach resonance) is observed in the open
channel involving different electronic orbitals. Noticeably, the behavior which
is observed in the position of resonance centers as a function of the relative
spin projection of the scattering particles reflects the SU(N) character of
interactions in the Yb atom. The strong interacting regime is achieved by
tuning the scattering length via this novel kind of resonance.
Hottopic Talk
Superradiant Mott insulator in the Dicke-Hubbard model
Andreas Hemmerich
Inst. für Laser-Physik, Uni Hamburg
Luruper Chaussee 149, 22761 Hamburg, Germany
hemmerich@physnet.uni-hamburg.de
It is well known that the bosonic Hubbard model possesses a Mott insulator
phase. Likewise, it is known that the Dicke model exhibits a self-organized
superradiant phase. By implementing an optical lattice inside of a high finesse optical cavity both models are merged such that an extended Hubbard
model with cavity-mediated infinite range interactions arises. In addition to
a normal superfluid phase, two superradiant phases are found, one of them
coherent and hence superfluid and one incoherent Mott insulating.
9
Talks
Solving a quantum many-body problem by experiment
Thomas Schweigler
Atominstitut, TU Wien
Stadionallee 2, 1020 Vienna, Austria
tschweigler@ati.ac.at
We experimentally study a pair of tunnel-coupled one-dimensional atomic superfluids, which realize the quantum sine-Gordon/massive Thirring models
relevant for a wide variety of disciplines from particle to condensed-matter
physics. From measured interference patterns we extract phase correlation
functions and analyze if, and under which conditions, the higher-order correlation functions factorize into lower ones. This allows us to characterize the
essential features of the model solely from our experimental measurements,
detecting the relevant quasiparticles, their interactions and the topologically
distinct vacua. The method is also used to investigate the non-equilibrium
dynamics following a quench in the tunnel-coupling between the superfluids.
Invited Talk
Rosensweig instability and quantum droplets in a strongly dipolar
BEC.
Igor Ferrier-Barbut
5. Physikalisches Institut Stuttgart
Pfaffenwaldring 57, 70569 Stuttgart, Germany
i.ferrier-barbut@physik.uni-stuttgart.de
Quantum many-body systems with dipole interactions are expected to feature many novel phenomena. In this talk we will report on the observation of
two of them, one expected and one unexpected. Our team explores dipolar
BECs of 164D y, characterized by a domination of the dipole interaction over
the contact interaction at the background level (away from resonances). We
first observe a finite wavelength instability of a BEC driven by the anisotropic
long-range interaction. This instability was expected and is related the “roton” minimum of the elementary excitations, it is in close similarity with the
Rosensweig instability of classical ferrofluids. Following this instability we
observe the formation of long-lived droplets in contradiction with the meanfield prediction that they should subsequently collapse. By systematically
studying these droplets in a waveguide configuration, we demonstrate that
quantum fluctuations play a strong role and in fact stabilize the droplets
against collapse.
10
Talks
Tuesday, February 23
Invited Talk
Controlling long-range interactions by Rydberg dressing
Christian Gross
MPQ
Hans-Kopfermann-Str. 1, 85748 Garching, Germany
christian.gross@mpq.mpg.de
Controlling strong long-range interactions in quantum gases enables the experimental study of rich quantum many-body physics, such as frustrated
quantum magnets or supersolids. One possibility to achieve this goal is near
resonant laser coupling to Rydberg states, thus, transferring the dipolar interaction between Rydberg atoms to the dressed atomic ground states. Here we
report on the observation of coherent Rydberg dressing by directly "imaging"
the induced interaction phase shift via many-body Ramsey interferometry.
We track the growth of correlations in a 2d array of 200 atoms and demonstrate control over the range and shape of the induced interaction potential.
Finally, we identify black body radiation induced coupling to nearby Rydberg states as the main source of decoherence in our system.
11
Talks
Invited Talk
Finding almost conserved local quantities in non-integrable
quantum systems
Maria Carmen Banuls
Max Planck Institut fuer Quantenoptik
Hans Kopfermann Str. 1, 85748 Garching, Germany
banulsm@mpq.mpg.de
The question of thermalization of closed quantum systems refers to whether
local expectation values attain stationary values, independent of the details of
the initial state, and it is of fundamental interest. Generically, non-integrable
systems, in which the only conserved local quantity is the energy density, are
expected to reach thermalization. But experimental and numerical results
have hinted at the existence of very slow time scales in systems without local
conserved quantities. Using tensor network techniques and exact diagonalization, we have shown how very large time scales can appear in the dynamics
of one dimensional spin chains. Our method finds operators evolving slower
than the slowest energy mode in a non-integrable system. The same method
can be applied to other scenarios, as that of many body localization, to find
local conserved quantities.
12
Talks
Hottopic Talk
Optimal shaking of optical lattices
Florian Mintert
Imperial College London
Imperial College London, London, UK
f.mintert@ic.ac.uk
We discuss the optimal design of driving patterns for optical lattices. There
are geometry dependent selection rules that limit the realisation of implementable dynamics, but Hamiltonians in accordance with these rules can be
implemented in a clean fashion with the help of polychromatic driving as we
demonstrate with the example of a Chern insulator in a deep optical lattice.
Invited Talk
Photon propagation by dipolar exchange
Thomas Pohl
Max-Planck-Institute for the Physics of Complex Systems
Noethnitzer Str. 38 , D-01187 Dresden, Germany
tpohl@pks.mpg.de
In this talk I will consider the propagation of light through a medium that
features strong dipolar interactions. Such interactions induce exchange of
excitations, i.e. spin wave components generated by propagating photons.
Already, the simple case of a single photon interacting with a single spin
wave reveals a number of surprising features, which will be discussed in this
talk. Recent experiments, utilizing exchange of high-lying atomic states in
a cold gas, demonstrate these effects and suggest promising applications for
the processing of single photons.
13
Talks
Invited Talk
Many-Body Physics in Cavity Quantum Electrodynamics
Giovanna Morigi
Saarland University
Campus E26, 66123 Saarbruecken, Germany
giovanna.morigi@physik.uni-saarland.de
In this talk I will review recent works on the dynamics of ultracold atoms in
the long-range potential mediated by the photons of a single-mode cavity. I
will highlight the features that emerge from the interplay between the longrange interaction and the wave nature of matter at low temperatures.
Invited Talk
Competing Quantum Phases in Bosonic Lattice Systems with
Rydberg Dressing
Walter Hofstetter
Institut für Theoretische Physik
Max-von-Laue-Str. 1, 60438 Frankfurt, Germany
hofstett@physik.uni-frankfurt.de
Recent experiments have shown that (quasi-)crystalline phases of Rydbergdressed quantum many body systems in optical lattices (OL) are within
reach. While conventional neutral atomic OL gases lack strong long-range
interactions, they arise naturally in Rydberg systems, due to the large polarisability of Rydberg atoms. In combination with the bosonic character of
the systems considered in our work, a wide range of quantum phases have
been predicted. Among them are a devil’s staircase of lattice-incommensurate
density waves, as well as the more exotic supersolid lattice order. High experimental tunability opens up a wide range of parameters to be studied. Based
on our previous analysis of the "frozen" gas case, we have studied the ground
state phase diagram at finite hopping amplitudes and in the vicinity of resonant Rydberg driving. Since different types of lattice-incommensurate order
are to be expected, we have applied a real-space extension of bosonic dynamical mean-field theory (RB-DMFT). This method allows a non-perturbative
treatment of local quantum correlations and also takes lowest-order nearestneighbour correlations into account. It therefore improves upon basic meanfield theories such as the Gutzwiller approximation (GA), yielding a rich
phase diagram which illustrates the competition between interaction and
condensation.
14
Talks
Hottopic Talk
A self-interfering clock as a "which path" witness
Ron Folman
Ben-Gurion University
Physics Department (POB 653), 84105 Beer Sheva, Israel
folman@bgu.ac.il
In Einstein’s general theory of relativity, time depends locally on gravity; in
standard quantum theory, time is global all clocks tick uniformly. We demonstrate a new tool for investigating time in the overlap of these two theories:
a self-interfering clock, comprising two atomic spin states. We prepare the
clock in a spatial superposition of quantum wave packets, which evolve coherently along two paths into a stable interference pattern. If we make the
clock wave packets tick at different rates, to simulate a gravitational time lag,
the clock time along each path yields "which path" information, degrading
the pattern’s visibility. In contrast, in standard interferometry, time cannot
yield "which path" information.
Published in Science 349, 1205 (2015).
15
Talks
Invited Talk
Interacting photons using Rydberg atoms
Paul Huillery
Department of Physics
Stockton Road, DH1 3LE Durham, UK
paul.huillery@durham.ac.uk
If photons are ideal carriers of information, they hardly interact together,
which makes the information difficult to process. This problem could be overcomed by mapping back and forth photons onto electronic states of atoms
and engenering suitable interactions between the latters. The field of Rydberg
non-linear optics aims to adress this challenge using two main ingredients.
Electromagnetically Induced Transparency (EIT) on one hand, which provides a way to coherently map photons onto atoms. The use of Rydberg
states on the other hand which provides strong atomic interactions. During
this talk, we will present some of the main results that have been obtained
in this field, including the observation of optical non-linearity at the single
photon level [1,2], generation of non-classical light [3] and realisation of single
photon optical transistors [4,5]. We will also present experimental progress
toward the realisation of interactions between photons which are spatially
separated.
[1]
[2]
[3]
[4]
[5]
J.D. Pritchard et al, Phys. Rev. Lett. 105, 193603 (2010)
T. Peyronel et. al., Nature 488, 57-60 (2012)
Y. O. Dudin et al, Science 336, 887-889 (2012)
H. Gorniaczyk et. al., Phys. Rev. Lett. 113, 053601 (2014)
D. Tiarks et al, Phys. Rev. Lett. 113, 053602 (2014)
16
Talks
Quantum Simulation of a Wilson lattice gauge theory
Christine Muschik
IQOQI
Technikerstrasse 21a, 6020 Innsbruck, Austria
christine.muschik@oeaw.ac.at
The quantum simulation of models from high-energy physics is a rapidly
growing field. A major interest is the simulation of gauge theories.
Wilson’s lattice gauge theory represents the most advanced, non-perturbative
technique to investigate the physics of strongly coupled gauge theories. However, numerical calculations are severely limited by the sign problem, which
has motivated intensive research on the question how gauge theories could
be simulated on a quantum simulator. We propose and experimentally study
the quantum simulation of a Wilson lattice gauge theory with trapped ions.
The scheme will build a strong bridge to the high-energy physics community
and allow for the direct comparison with quantities discussed in the lattice
gauge theory literature.
17
Talks
Wednesday, February 24
Invited Talk
Progress in quantum information processing with trapped ions at
NIST
Dietrich Leibfried
NIST
325 Broadway, 80305 Boulder, USA
dil@boulder.nist.gov
Most basic requirements for quantum information processing and quantum
simulation have been demonstrated for trapped ions, with two big challenges
remaining: Improving operation fidelity and scaling up to larger numbers of
qubits. In the last few years, operation fidelities have steadily increased with
single qubit rotation errors per π-pulse close to 10−6 for microwave operations and 10−4 for laser-based Raman-transitions on hyperfine ground state
qubits. Laser-based two-qubit entanglement schemes have demonstrated fidelities of deterministically produced Bell states of larger than 0.998. Entanglement operations with microwaves in miniaturized surface electrode traps
have recently demonstrated Bell state fidelities of 0.993. At NIST, scaling
towards larger systems is based on moving ion-qubits through a multi-zone
trap array and sympathetically cooling them with a second ion species. Microfabrication approaches to ion-trap-arrays have yielded structures that should
be capable of holding and manipulating large numbers of ions. I will give a
brief overview over technical developments and recent experiments in quantum information processing and quantum simulation with trapped ions at
NIST, highlighting the progress due to improved laser sources, better laserbeam control by utilizing high-power single-mode UV fibers, reductions in
anomalous heating and improvements of cooling, transport and quantum
control of multi-species ion crystals.
This work has been supported by IARPA, DARPA, ONR, and the NIST
Quantum Information Program.
18
Talks
Invited Talk
Quantum logic with molecular ions
Piet Schmidt
PTB/Leibniz Universität Hannover
Bundesallee 100, 38116 Braunschweig, Germany
Piet.Schmidt@quantummetrology.de
Precision spectroscopy is a driving force for the development of our physical
understanding. However, only few atomic and molecular systems of interest
have been accessible for precision spectroscopy in the past, since they miss a
suitable transition for laser cooling and internal state detection. This restriction can be overcome in trapped ions through quantum logic spectroscopy.
I will show how the internal state of a molecular ion can be detected nondestructively on a co-trapped cooling ion by implemented a quantum logic
algorithm involving only coherent laser manipulation on the molecular ion.
This represents a first step towards extending the exquisite control achieved
over selected atomic species to much more complex molecular ions.
An enhanced quantum interface through collective ion-cavity
coupling
Tracy Northup
Experimentalphysik Innsbruck
Technikerstrasse 25, 6020 Innsbruck, Austria
Tracy.Northup@uibk.ac.at
Optical cavities offer a coherent interface between matter and light, enabling
the transfer of quantum information onto photons for long-distance distribution. For example, a quantum state can be faithfully mapped from a trapped
ion onto the polarization state of a cavity photon [1]. I will describe how this
transfer can be improved by taking advantage of a collective effect between
multiple ions, namely, superradiant emission into the cavity. By constructing an interface based on entangled ions, one can thus relax the technical
requirements for the faithful mapping of quantum information [2]. Finally,
prospects for linking together distant ions in cavities via a quantum network
will be discussed.
[1] A. Stute et al., Nature Photon. 7, 219 (2013)
[2] B. Casabone et al., Phys. Rev. Lett. 114, 023602 (2015)
19
Talks
Hottopic Talk
Topological phases due to density dependent tunnelings in
periodically driven systems
Jakub Zakrzewski
Jagiellonian University
Lojasiewicza 11, 30-348 Krakow, Poland
kuba@if.uj.edu.pl
Two species of attractively interacting fermions in optical lattice are considered. Using periodic driving, role of density-dependent s – p tunnelings
is enhanced while standard tunnelings are killed. Composites of two species
form then an emergent lattice in which excess fermions move.
For 1D system at half filling, composites form a density wave and excess
fermions move in the effective Hamiltonian (dimer Rice-Mele) with controlled
defects where topologically protected localized modes appear [1].
For 2D triangular lattice [2] at 1/3-filling the excess fermions move in an
emergent Dice lattice. One may realize either anomalous Hall effect or its
quantized version.
[1] A. Przysiezna et al., New. J. Phys. 17, 013018 (2015).
[2] O. Dutta et al. Sci. Rep. 5, 11060 (2015).
Invited Talk
Many-body quantum optics with fermions
Philipp Strack
University of Cologne
Zülpicher Str. 77a, 50937 Cologne, Germany
strack@thp.uni-koeln.de
We propose and describe far-from-equilibrium phases of matter by interfacing quantum degenerate fermionic atoms with quantized, optical light fields.
20
Talks
Invited Talk
Quantum phases emerging from competing short- and long-range
interactions in an optical lattice
Manuele Landini
ETH zurich
Otto-Stern-weg 1, 8093 Zurich, Switzerland
landinim@phys.ethz.ch
Examples of competition between interactions acting on different length
scales range from the folding mechanisms of proteins to the appearance of
stripe phases in quantum matter. Theoretical characterization of such emerging structures is often challenging even if simple models are used. Here we
experimentally realize a bosonic lattice model with competing short- and
infinite-range interactions, and observe the appearance of four distinct phases
- a superfluid, a supersolid, a Mott insulator and a charge density wave. Our
system is based on an atomic quantum gas trapped in an optical lattice inside
a high finesse cavity. When probing the transition between the Mott insulator and the charge density wave, we discovered a behaviour characteristic of
a first order phase transition.
21
Talks
Hottopic Talk
Supermode-polariton condensation in a multimode cavity
QED-BEC system
Alicia Kollar
Stanford University
969 Lawrence Lane, Unit 2, 94303 Palo Alto, USA
akollar@stanford.edu
Investigations of many-body physics in an AMO context often employ a static
optical lattice to create a periodic potential. Such systems, while capable of
exploring, e.g., the Hubbard model, lack the fully emergent crystalline order
found in solid state systems whose stiffness is not imposed externally, but
arises dynamically. Our multimode cavity QED experiment is introducing a
new method of generating fully emergent and compliant optical lattices to
the ultracold atom toolbox and provides new avenues to explore quantum
liquid crystalline order. Looking forward, spin glasses may arise due to the
oscillatory, frustrated, and tunable-range interactions mediated by the photons in the multimode optical cavity. It will thus be possible to use spinful
atoms in cavities to realize models of frustrated and/or disordered spin systems, including neuromorphic computation in the context of the Hopfield
associative memory. We will present our first experimental result, the observation of a supermode-polariton condensate via a supermode superradiant
phase transition.
22
Talks
Invited Talk
Light, sound, and topology
Florian Marquardt
Institute for Theoretical Physics II
Staudtstr. 7 , 91058 Erlangen, Germany
Florian.Marquardt@physik.uni-erlangen.de
The interaction between radiation and mechanical motion on the nanoscale
is now being studied intensively. Known as optomechanics, this field promises
applications in quantum communication, sensitive measurements, and fundamental studies of quantum physics. After a general introduction, I will turn
to some recent ideas of ours that envisage controllable transport of photons
and phonons in so-called optomechanical arrays. Once realized, these systems
could e.g. feature engineered chiral edge channels for light and sound that
are topologically protected against disorder-scattering.
[1] Cavity optomechanics, M. Aspelmeyer, T. Kippenberg, and F. Marquardt,
Reviews of Modern Physics 86, 1391 (2014)
[2] Topological Phases of Sound and Light, V. Peano, C. Brendel, M. Schmidt,
and F. Marquardt, Phys. Rev. X 5, 031011 (2015)
23
Talks
Thursday, February 25
Invited Talk
Breaking Quantum and Thermal Limits on Precision
Measurements
James Thompson
JILA
JILA/Univ. of Colorado, 440UCB, 80309 Boulder, USA
jkt@jila.colorado.edu
We are exploring how to use collective correlations and entanglement between many atoms to overcome quantum and thermal limits on precision
measurements. In the first portion of my talk, I will present a path toward a
10000 times reduced sensitivity to the thermal mirror motion that limits the
linewidth of today’s best lasers. By utilizing narrow atomic transitions [1],
the laser’s phase information is primarily stored in the atomic gain medium
rather than in the vibration-sensitive cavity field [2]. To this end, I will present
the first observation of lasing based on the 7.5 kHz [3] and 1 mHz linewidth
optical-clock transitions in a laser-cooled ensemble of strontium atoms. In
the second portion of my talk, I will describe how we use collective measure√
ments to surpass the standard quantum limit on phase estimation 1/ N
for N unentangled atoms. We achieve a directly observed reduction in phase
variance relative to the standard quantum limit of as much as 17.7(6) dB
[4,5]. I will discuss first steps toward applying the same technique to create
entanglement on the mHz optical-clock transition in strontium via measurements of the magnitude of a well-resolved collective vacuum Rabi splitting
on the 7.5 kHz transition [6].
[1] Prospects for a millihertz-linewidth laser, D. Meiser, J. Ye, D. R. Carlson,
M. J. Holland, Phys. Rev. Lett. 102, 063601 (2009)
[2] A steady-state superradiant laser with less than one intracavity photon, J.
G. Bohnet, Z. Chen, J. M. Weiner, D.Meiser, M. J. Holland, J. K. Thompson,
Nature 484, 78-81 (2012)
[3] A Cold-Strontium Laser in the Superradiant Crossover Regime , M. A.
Norcia, J. K. Thompson, arXiv:1510.06733 (2015)
[4] Reduced spin measurement back-action for a phase sensitivity ten times
beyond the standard quantum limit, J. G. Bohnet, K. C. Cox, M. A. Norcia,
J. M. Weiner, Z. Chen, J. K. Thompson, Nature Photonics, 8, 731 (2014)
[5] Deterministic Squeezed States with Joint Measurements and Feedback, K.
C. Cox, G. P. Greve, J. M. Weiner, J. K. Thompson, arXiv:1512.02150 (2015)
[6] Strong Coupling on a Forbidden Transition in Strontium and Nondestructive Atom Counting, M. A. Norcia, J. K. Thompson, arXiv:1506.02297 (2015)
24
Talks
Invited Talk
Cavity Quantum Electrodynamics: A Quantum Optics Chameleon
Gerhard Rempe
Max Planck Institute of Quantum Optics
Hans-Kopfermann-Str. 1, 85748 Garching, Germany
gerhard.rempe@mpq.mpg.de
Electromagnetic resonators provide unparalleled possibilities in controlling
the interaction between single atoms and single photons. The recently developed techniques for controlling also the position and the momentum of the
atoms inside an optical resonator now open up new experimental avenues for
genuine quantum-mechanical experiments. Particularly exciting possibilities
concern long-distance quantum networking and scalable quantum computation. The talk will highlight some recent achievements like the nondestructive
detection of an optical photon, the heralded and efficient storage of a flying
optical qubit in a stationary atomic qubit, and – arguably most interesting
– the realization of quantum gates with individually addressable atomic and
photonic qubits.
25
Talks
One, two and three photons from a nanowire
Gregor Weihs
Experimentalphysik Innsbruck
Technikerstrasse 25, 6020 Innsbruck, Austria
gregor.weihs@uibk.ac.at
Producing advanced quantum states of light is a priority in quantum information technologies. While remarkable progress has been made on single
photons and photon pairs, multipartite correlated photon states are usually produced in purely optical systems by postselection or cascading, with
extremely low efficiency and exponentially poor scaling. Multipartite states
enable improved tests of the quantum mechanics foundations as well as implementations of complex quantum optical networks and protocols. It would
be favorable to generate these states directly using solid-state systems, for
better scaling, simpler handling, and the promise of reversible transfer of
quantum information between stationary and flying qubits.
In our work, we have shown that quantum dots in nanowires are extremely efficient sources of single photons and entangled photon pairs. Most recently, we
used ground states of two optically active coupled InAsP quantum dot insertions in an InP nanowire to directly produce photon triplets. The formation
of a triexciton leads to a triple cascade recombination and sequential emission of three photons with measurable correlations. This source surpasses the
rates of all earlier reported sources, in spite of the moderate efficiency of our
detectors. Our structure and data represent a breakthrough towards implementing multipartite photon entanglement and multi-qubit readout schemes
in solid state devices, suitable for integrated quantum information processing.
26
Talks
Hottopic Talk
Micro- and nano-optomechanics towards quantum state and
hybrid devices
Tristan Briant
UPMC, LKB
LKB, Campus Jussieu, BC74, 75252 Paris, France
tristan.briant@upmc.fr
Reaching the quantum ground state of macroscopic and massive mechanical
objects is a major experimental challenge at the origin of the rapid emergence of cavity optomechanics. We develop a new generation of optomechanical devices, either based on microgram 1-mm long quartz micropillar with
very high mechanical quality factor or on 100-pg photonic crystal suspended
nanomembranes. We expect to reach the ground state of such optomechanical resonators combining cryogenic and radiation-pressure cooling. We also
investigate the possibility to develop an hybrid platform which may be very
helpful for quantum engineering and quantum information processing, by
coupling our suspended nanomembranes to cold atoms or to microwave circuits.
Invited Talk
Quantum optics width deterministically fabricated quantum dot
microlenses
Stephan Reitzenstein
TU Berlin
Hardenbergstrasse 36, 10623 Berlin, Germany
sreitzenstein@gmx.net
Bright non-classical light sources emitting single and indistinguishable photons on demand constitute essential building blocks towards the realization
of quantum communication networks. In this talk, I will report on efficient
single photon sources based on deterministically fabricated single quantum
dot (QD) microlenses. Close to ideal performance of the non-classical lightsources in terms of photon extraction efficiency, high suppression of multiphoton events and a high degree of indistinguishability is ensured by applying
in-situ electron beam lithography [1] with process yield higher than 90%.
[1] M. Gschrey et al., Nature Communications 6, 7662 (2015).
27
Talks
Invited Talk
Superfluidity and interactions in topologically and geometrically
non-trivial bands
Päivi Törmä
Aalto University
Department of Applied Physics, P.O.Boz 15100, 76 Aalto, Finland
paivi.torma@aalto.fi
Fermions in flat bands are predicted to reach non-zero pairing gaps at high
temperatures. Superfluidity, however, has been an open question in flat bands
since the usual group velocity is zero. We provide a general expression for the
superfluid weight D s of a multiband superconductor that is applicable also to
topologically nontrivial bands with nonzero Chern number C [1]. We find that
an invariant calculated from the Bloch functions gives the superfluid weight in
a flat band, with the bound Ds ≤ |C|. Thus, even a flat band can carry finite
superfluid current, provided the Chern number is nonzero. Intriguingly, we
find that the superfluid density is connected to the quantum geometric tensor
and quantum metric. As an example, we provide Ds for the time-reversal
invariant attractive Harper-Hubbard model that can be experimentally tested
in ultracold gases. We have recently shown that also geometric effects can
lead to C=0 flat bands that may support superfluidity [2]. Furthermore,
we study the effect of repulsive interactions on the Haldane-Hubbard model
recently realized in ultra-cold gases [3]. By a combined dynamical mean-field
theory and exact diagonalization study, we find a new phase with the Chern
number C=1 [4]. This phase is associated with a spontaneous symmetry
breaking where one of the spin-components is in the Hall state and the other
in the band insulating state.
[1] S. Peotta and P. Törmä, Nat. Comm. 6, 8944 (2015)
[2] A. Julku, S. Peotta, T.I. Vanhala, D-H. Kim, and P. Törmä, in preparation
[3] G. Jotzu, M. Messer, R. Desbuquois, M. Lebrat, T. Uehlinger, D. Greif,
and T. Esslinger, Nature 515, 237 (2014)
[4] T.I. Vanhala, T. Siro, L. Liang, M. Troyer, A. Harju, and P. Törmä,
Topological phase transitions in the repulsively interacting Haldane-Hubbard
model, arXiv:1512.08804 (2015)
28
Talks
Hottopic Talk
Demonstration of Deterministic Photon-Photon Interactions
based on Single-Photon Raman Interaction
Barak Dayan
Weizmann Institute of Science
Weizmann Institute of Science, 76100 Rehovot, Israel
barak.dayan@gmail.com
I will present our demonstration of a passive scheme for deterministic interactions between a single photon and a single atom. Relying on single-photon
Raman interaction (SPRINT), this control-fields free scheme swaps a flying
qubit, encoded in the two possible input modes of a photon, with a stationary qubit, encoded in the two ground states of the atom, and can be also
harnessed to perform universal quantum gates. Using SPRINT we experimentally demonstrated all-optical switching of single photons by single photons, and deterministic extraction of a single photon from an optical pulse.
Applicable to any atom-like Lambda system, SPRINT provides a versatile
building block for scalable quantum networks based on completely passive
nodes interconnected and activated solely by single photons.
A significant-loophole-free test of Bell’s theorem with entangled
photons
Sören Wengerowsky
IQOQI Vienna and University of Vienna
Boltzmanngasse 3, 1090 Vienna, Austria
soeren.wengerowsky@univie.ac.at
Local realism is the worldview in which physical properties of objects exist
independently of measurement and where physical influences cannot travel
faster than the speed of light. Bell’s theorem states that this concept is incompatible with the predictions of quantum mechanics, as is expressed in
Bell’s inequalities. Previous experiments strongly supported the quantum
predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. We report a Bell test that closes the most
significant of these loopholes simultaneously. Using an optimized source of
entangled photons, rapid setting generation, and highly efficient detectors,
we observe a violation of a Bell inequality with high statistical significance,
equivalent to 11.5 standard deviations.
29
Talks
Dynamical Self-Ordering of Superfluids and Light
Francesco Piazza
ITP Innsbruck
Technikerstrasse 25, 6020 Innsbruck, Austria
francesco.piazza@uibk.ac.at
The strong back-action of an optically dense medium onto the electromagnetic field gives rise to interesting phenomena. One example is atomic selfordering, whereby the particles spontaneously form a stationary Bragg pattern maximising the light scattering. It has been experimentally observed
with thermal gases and more recently also with Bose-Einstein condensates
(BECs) inside optical resonators. In this talk, we present some new regimes of
self-ordering with BECs, extending the so far explored regimes to two novel
scenarios. Firstly, we will introduce a situation in which self-ordering appears
as a dynamical limit-cycle phase evolving into chaos, whereby the superfluid
nature of the BEC manifests itself through phase-slippage and turbulence.
Secondly, we will consider a free-space configuration where no pre-selected
light modes are imposed, so that self-ordering amounts to a real crystallisation of both the BEC, into a supersolid, and the light field, into an optical
lattice with phonons.
30
Talks
Friday, February 26
Invited Talk
Frequency ratios of optical lattice clocks at the 17th decimal place
Hidetoshi Katori
The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, 113-8656 Tokyo, Japan
katori@amo.t.u-tokyo.ac.jp
Optical lattice clocks [1] benefit from a low quantum-projection noise by simultaneously interrogating a large number N of atoms, which are trapped in
an optical lattice tuned to the “magic wavelength” to largely cancel out light
shift perturbation in the clock transition. N ≈ 103 atoms enable the clocks to
achieve 10−18 instability in a few hours of operation, allowing intensive investigation and control of systematic uncertainties. Optical lattice clocks have
reached inaccuracies approaching 10−18 [2, 3]. It is now the uncertainty of the
SI second (∼ 10−16 ) itself that restricts the measurement of the absolute frequencies of such optical clocks [4, 5]. Direct comparisons of optical clocks are,
therefore, the only way to investigate and utilize their superb performance
beyond the current SI second. In this presentation, we report on frequency
comparisons of optical lattice clocks with neutral strontium (87 Sr), ytterbium
(171 Yb) and mercury (199 Hg) atoms. By referencing cryogenic Sr clocks [2], we
determine frequency ratios, νYb /νSr and νHg /νSr [6], of a cryogenic Yb clock
and a Hg clock with uncertainty at the mid 10−17 level. Such ratios provide
an access to search for a temporal variation of the fundamental constants.
We also present remote comparisons between cryogenic Sr clocks located at
RIKEN and the University of Tokyo over a 30-km-long phase-stabilized fibre
link [7]. The gravitational red shift ∆ν/ν0 ≈ 1.1 × 10−18 ∆h(cm)−1 reads out
the height difference ∆h ∼ 15 m between the two clocks with uncertainty of
5 cm, which demonstrates a step towards relativistic geodesy [8].
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
H. Katori, Nature Photon. 5, 203 (2011).
I. Ushijima et al., Nature Photon. 9, 185 (2015).
B. J. Bloom et al., Nature 506,71 (2014).
R. Le Targat et al., Nature Commun. 4, 2109 (2013).
S. Falke et al., New J. Phys. 16, 073023 (2014).
K. Yamanaka et al., Phys. Rev. Lett. 114, 230801 (2015).
T. Akatsuka et al., Jpn. J. Appl. Phys. 53, 032801 (2014).
A. Bjerhammar, J. Geod. 59, 207 (1985).
31
Talks
Invited Talk
Searching for ultralight dark matter with atomic spectroscopy
and nuclear resonance
Dmitry Budker
Helmholtz Institute Mainz
Friedrichsstraße 33, 55124 Mainz, Germany
budker@uni-mainz.de
Axions, axion-like particles (ALPs), dilatons, and other ultralight (masses
from 10−4 down to 10−22 eV) particles have been discussed as possible candidates for dark matter. An interesting feature of these ideas is that they
lead to predictions of potentially observable transient and oscillating effects.
I will describe how we are looking for these as well as the relation of such
experiments to tests of fundamental symmetries (P, CP, T, CPT . . . ).
Inhibition of superradiance and light-matter decoupling in circuit
QED
Peter Rabl
Atominstitut, TU Wien
Stadionallee 2, 1020 Vienna, Austria
peter.rabl@ati.ac.at
The existence or non-existence of a superradiance phase transition in the
ground state of a multi-atom cavity QED systems has generated many debates and contradicting conclusions. In view of recent experiments with superconducting qubit-cavity systems operated in the ultra-strong coupling
regime, this question is no longer only of theoretical relevance. Here I will
present a microscopic derivation of the Dicke model in circuit QED and show
that the usually neglected qubit-qubit interaction (rather than the often discussed A2 -term) cause a suppression of superradiance and can further lead to
a complete light-matter decoupling in the limit of very strong interactions.
32
Talks
Hottopic Talk
Weak measurements and quantum optical lattices for ultracold
bosons and fermions
Igor Mekhov
University of Oxford
Parks Road, Dep of Physics, OX1 3PU Oxford, UK
Igor.Mekhov@physics.ox.ac.uk
We show that the quantum backaction of weak global measurement constitutes a novel source of competitions in many-body systems (in additions
to standard short-range tunnelling and interactions in lattices). This leads
to novel dynamical effects: multimode oscillations of macroscopic superposition states, nonlocal non-Hermitian Zeno dynamics, long-range correlated
pair tunnelling, protection and break-up of fermion pairs, as well as generation of antiferromagnetic states. Quantization of optical lattice potentials
enables quantum simulations of various long-range interacting systems unobtainable using classical optical lattices. It leads to new quantum phases
(dimers, trimers, etc. of matter waves) beyond density orders (e.g. supersolids) utilizing collective light-matter interaction.
Invited Talk
The Quantum Pigeonhole Principle
Sandu Popescu
University of Bristol
Tyndall Av, BS8 1TL Bristol, UK
s.popescu@bristol.ac.uk
The pigeonhole principle: "If you put three pigeons in two pigeonholes at least
two of the pigeons end up in the same hole" is an obvious yet fundamental
principle of Nature as it captures the very essence of counting. Here however
we show that in quantum mechanics this is not true! We find instances when
three quantum particles are put in two boxes, yet no two particles are in the
same box. Furthermore, we show that the above ”quantum pigeonhole principle” is only one of a host of related quantum effects, and points to a very
interesting structure of quantum mechanics that was hitherto unnoticed. Our
results shed new light on the very notions of separability and correlations in
quantum mechanics and on the nature of interactions. It also presents a new
role for entanglement, complementary to the usual one. Finally, interferometric experiments that illustrate our effects are proposed.
33
Talks
Quantum Simulation with Superconducting Qubits
Gerhard Kirchmair
IQOQI Innsbruck
Technikerstrasse 21a, 6020 Innsbruck, Austria
gerhard.kirchmair@uibk.ac.at
In this talk I want to present the research activities of the Superconducting
Quantum Circuits group at the Institute for Quantum Optics and Quantum Information in Innsbruck towards quantum simulation with Transmon
qubits. I will give an introduction to circuit quantum electrodynamics and
the 3D architecture. I will show how we want to use this architecture to realize a platform for quantum many body simulations of dipolar XY models
using state of the art circuit QED technology. Our basic building blocks are
3D Transmon qubits where we use the naturally occurring dipolar interactions to realize interacting spin systems.
Hottopic Talk
Controlled Ensembles of Ultracold Formaldehyde Molecules
Martin Zeppenfeld
MPI for Quantum Optics
Hans Kopfermann Str. 1, 85748 Garching, Germany
martin.zeppenfeld@mpq.mpg.de
Cooling molecules to ultracold temperatures enables fascinating applications
such as ultracold chemistry and investigation of dipolar quantum gases. We
apply opto-electrical Sisyphus cooling, a general cooling technique for polar molecules, to formaldehyde. We thereby generate an ensemble of roughly
300000 electrically trapped molecules at a temperature of about 400µK. The
combination with optical pumping via a vibrationally excited state provides
control of the rotational state, resulting in over 80% of molecules in a single
rotational M-sublevel. Our experiment provides excellent conditions for precision spectroscopy and investigation of ultracold collisions.
34
Talks
Quantum enhancements of learning agents
Vedran Dunjko
Institute for Theoretical Physics
Technikerstrasse 21a, 6020 Innsbruck, Austria
Vedran.Dunjko@uibk.ac.at
The interplay between classical learning theory and quantum mechanics has
been gaining an ever increasing interest in the recent years. In this talk, we
will discuss some of the recent results of the research community, which have
explored both directions of this interplay. In one direction, we will consider
the advantages of utilizing machine learning to enhance quantum experiments. In the reverse direction, we will consider the potential of utilizing
quantum effects to enhance learning performance. Following this, we will focus on some of our more recent results, which concern quantum speed-ups of
active learning in the Projective Simulation model for Artificial Intelligence,
and also the general capacity of quantum interactions to enhance the learning properties of artificial learning agents.
Invited Talk
Dicke subradiance in a large cloud of cold atoms
Robin Kaiser
CNRS
1361 route des Lucioles, 6560 Valbonne, France
robin.kaiser@inln.cnrs.fr
Since Dicke’s seminal paper on coherence in spontaneous radiation by atomic
ensembles, superradiance has been extensively studied. Subradiance, on the
contrary, has remained elusive, mainly because subradiant states are weakly
coupled to the environment and are very sensitive to nonradiative decoherence processes.Here we report the direct observation of subradiance in an
extended and dilute cold-atom sample containing a large number of particles. We use a far detuned laser to avoid multiple scattering and observe the
temporal decay after a sudden switch-off of the laser beam. After the fast
decay of most of the fluorescence, we detect a very slow decay, with time
constants as long as 100 times the natural lifetime of the excited state of
individual atoms. This subradiant time constant scales linearly with the cooperativity parameter, corresponding to the on-resonance optical thickness
of the sample, and is independent of the laser detuning, as expected from a
coupled-dipole model.
35
Posters
Posters
Quantum Superposition at the half-meter scale
Peter Asenbaum
Stanford University
382 Via Pueblo Mall, 94305 Stanford, USA
asenbaum@stanford.edu
In matter wave interferometers, large wave packet separation is impeded by
the need for long interaction times and large momentum beam splitters,
which cause susceptibility to dephasing and decoherence. We use light-pulse
atom interferometry to realize quantum interference with wave packets separated by up to 54 cm on the time scale of 1 s. Large quantum superposition
states are vital to exploring gravity with atom interferometers in greater
detail, e.g. tests of the equivalence principle.
Magnetic double slits for a magnetic skatepark
Prasanna Venkatesh Bala
IQOQI
Technikerstrasse 21a, 6020 Innsbruck, Austria
Prasanna.Venkatesh@uibk.ac.at
In this poster we discuss a key component of a proposal for an on-chip all magnetic set up to create large superposition and observe the quantum interference of a massive superconducting sphere (mass ∼ 1014 amu). The idea is to
create a magnetic double slit by allowing the superconducting sphere, which
is a perfect diamagnet below its critical temperature, to dispersively interact
with a transmon qubit such that a flux-dependent coupling proportional to
the squared position of the sphere is realized. A homodyne measurement of
the output field of the transmon actualizes a continuous measurement of the
squared position of the sphere – a magnetic double slit. In contrast to usual
double slits for massive quantum mechanical objects in this scenario, the
slit separation is a dynamical variable set by the measurement outcome and
post-selection can be used to restrict to a given range of slit sizes required for
the proposal. The larger aim of the proposal is to show that interference of
such massive objects can be used to falsify gravity-induced decoherence and
other paradigmatic collapse models that predict a breakdown of quantum
superposition principle at large mass scales.
37
Posters
Bell Correlations in a Bose-Einstein Condensate
Jean-Daniel Bancal
University of Basel
Klingerlbergstrasse 82, CH-4056 Basel, Switzerland
jdbancal.physics@gmail.com
Tremendous progress has been made recently in characterizing many-body
systems through the quantum correlations between their constituent particles. While entanglement is routinely observed in many systems, we report
here the detection of stronger correlations - namely Bell correlations - between the spins of about 480 atoms in a Bose-Einstein condensate. We derive a Bell correlation witness from a recent many-particle Bell inequality
involving one- and two-body correlation functions only. Our measurement
on a spin-squeezed state exceeds the threshold for Bell correlations by 3.8
standard deviations. Concluding the presence of Bell correlations is unprecedented for an ensemble containing more than a few particles.
Majorana fermions in atomic-molecular systems at finite
temperature and in the presence of a noise.
Mikhail Baranov
IQOQI
Technikerstraße 21a, 6020 Innsbruck, Austria
Mikhail.Baranov@uibk.ac.at
The effects of quantum and thermal fluctuations, as well as of global and
local noises, on the Majorana edge states in networks of topological atomicmolecular wires are discussed.
38
Posters
Atomic clocks and interferometers with a PLL on the coherent
atomic superposition
Andrea Bertoldi
LP2N - Institut d’Optique
rue Mitterrand, 33400 Talence, France
andrea.bertoldi@gmail.com
In an atomic interferometer the phase evolution of a local oscillator is compared to that of an atomic superposition state. A tradeoff must be found between the duration of the comparison interval, if longer sensitivity increases,
and the avoidance of readout ambiguities, the measurement gives the phase
projection so phase wraps go undetected. This issue limits the sensitivity
of optical lattice clocks and of atomic gravimeters. We bypassed the tradeoff
using coherence preserving measurements and phase corrections, and demonstrate the phase lock of a clock oscillator to an atomic superposition state
[PRX 5, 021011 (2015)]. The protocol could improve the sensitivity of atomic
clocks limited by local oscillator noise and could be applied in inertial sensors
based on atom interferometry.
Incompressible polaritons in a flat band
Matteo Biondi
ETH Zurich
Wolfgang-Pauli-Str. 27, 8093 Zurich, Switzerland
mbiondi@itp.phys.ethz.ch
We present theoretical and experimental results on geometrically frustrated
non-equilibrium photonic lattices. In a theoretical work (PRL 115,143601)
we study the interplay of frustration and interactions in a polaritonic flat
band system. We engineer correlations in such a driven, dissipative system
by quenching the kinetic energy through frustration. This produces an incompressible state of photons characterized by short-range density-wave order with period doubling. We propose a circuit QED realization tunable insitu. We also discuss the first experiment on polariton condensation in a flat
band (arXiv 1505.05652). Due to the infinite effective mass, the condensate
is highly sensitive to disorder and fragments in localized modes, identified by
interferometric and spectral measurements.
39
Posters
Microscopic observation of degenerate fermionic lattice gases
Martin Boll
MPQ
Hans-Kopfermann Straße 1, 85748 Garching, Germany
martin.boll@mpq.mpg.de
We report on local observation of degenerate gases of fermions in an optical
lattices. We probe the gas with single-site resolution using a new generation quantum gas microscope avoiding the common problem of light induced
losses. In the band insulating regime, we measure a strong local suppression
of particle number fluctuations and a low local entropy per atom. Our work
opens a new avenue for studying quantum correlations in fermionic quantum
matter both in and out of equilibrium.
Developing portable ion trap magnetic field quantum sensors
Harry Bostock
Sussex University
Falmer road, BN1 9RH Brighton, UK
h.bostock@sussex.ac.uk
Highly sensitive magnetometers in the DC - GHz frequency range have uses
such as detecting explosives and drugs and can be a biological scanner. Single
trapped ytterbium ions have already successfully been used to sense magnetic
fields with sensitivities of 4pT H −1/2 for AC magnetic fields. We will present
progress towards making a portable, highly sensitive device based on said
method. For quantum sensing of magnetic fields with trapped ions, increasing
the number of trapped ions and coherence time improves sensitivity. We will
describe a design capable of trapping more than 100 ions along with progress
towards miniaturized ion trap sub systems technologies that are required for
a portable device.
40
Posters
New physics searches with atomic systems
Loukourgos Bougas
Helmholtz Institut-Mainz
Johann Joachim Becherweg 36, 55128 Mainz, Germany
naleefer@uni-mainz.de
The nature of dark matter and dark energy is one of the most exciting open
questions in physics today. Our recent work has shown that atomic systems
are excellent candidates for constraining a theoretical models where dark
matter is an ultralight particle with a macroscopic de Broglie wavelength. We
present initial constraints on such models from radio-frequency spectroscopy
of dysprosium, and discuss how these constraints may be improved by optical
clocks based on ions or atoms.
Local probing of the Hubbard model in two-dimensions
Ferdinand Brennecke
Uni Bonn
Wegelerstrasse 8, 53115 Bonn, Germany
brennecke@uni-bonn.de
Quantum gases of interacting fermionic atoms in optical lattices promise to
shed new light on the low-temperature phases of Hubbard-type models, such
as spin-ordered phases or possible d-wave superconductivity. We experimentally study the physics of the Hubbard model by loading a quantum degenerate two-component Fermi gas of 40K atoms into a three-dimensional optical
lattice geometry. Using high-resolution absorption imaging combined with
radio-frequency spectroscopy we are able to resolve the in-situ distribution
of singly and doubly occupied lattice sites within a single two-dimensional
layer. We will report on the observation of the fermionic Mott insulator and
a measurement of the equation of state for the repulsive Hubbard model in
two dimensions.
41
Posters
Atom-field dressed states in slow-light waveguide QED
Giuseppe Calajo
Tu Wien, atomic institute
Stadionallee 2, 1020 Vienna, Austria
giuseppe.calajo@ati.ac.at
We discuss the properties of atom-photon bound states in waveguide QED
systems consisting of single or multiple atoms coupled strongly to a finitebandwidth photonic channel. Such bound states are formed by an atom and
a localized photonic excitations and represent the continuum analog of the
familiar dressed states in single-mode cavity QED. In this work we present
a detailed analysis of the linear and nonlinear spectral features associated
with single- and multi-photon dressed states and show how the formation of
bound states affects the waveguide-mediated dipole-dipole interactions between separated atoms. Our results provide a both qualitative and quantitative description of the essential strong-coupling processes in waveguide QED
systems.
Ultracold atoms on a superconducting atomchip
Fritz Diorico
Atominsitut TU Wien
Stadionallee 2, 1020 Vienna, Austria
fdiorico@ati.ac.at
We present the realization of a robust magnetic transport scheme to bring
3 × 108 ultracold 87 Rb atoms into a 4K cryostat. The sequence starts with
standard laser cooling and trapping of 87 Rb atoms, transporting first horizontally and then vertically through the radiation shields into a cryostat
by a series of normal- and superconducting magnetic coils. After subsequent
precooling in a QUIC trap, about 3 × 106 atoms at 30µK are loaded on
a superconducting atomchip. This can be built from any superconducting
material. Currently, we have various designs of Niobium and YBCO atomchips fabricated with features either for cQED with microwave resonators
and ultracold atoms or novel superconducting traps using the remnant magnetization of the superconducting surface (vortex-like traps).
42
Posters
Symmetric Suppression in Many-Body Quantum Interferences
Christoph Dittel
Institut für Experimentalphysik
Technikerstraße 25d, 6020 Innsbruck, Austria
christoph.dittel@uibk.ac.at
We investigate how symmetry considerations in many-boson scattering experiments allow the formulation of symmetry suppression laws which predict
events occurring with zero probability due to constructive interference. In
particular, we theoretically formulate and experimentally test a suppression
law, based uniquely on the symmetries of the setup, leaving the exact form of
the scattering matrix open. Since this suppression relies on genuine N-body
interference, it represents a stringent certification criterion that can be used
to ensure the functionality of boson-samplers. Moreover, calculating which
events are suppressed and testing the suppression for a few such events is
efficient and scalable to very large particle numbers in practice.
Quantum Criticality of Coherently Driven Open Systems
Peter Domokos
Hungarian Academy of Sciences
Konkoly Thege Miklós út 29-33, 1121 Budapest, Hungary
domokos.peter@wigner.mta.hu
Quantum critical behavior can appear in coherently driven dissipative systems which cannot be, in general, mapped onto an effective Hamiltonian
system. It is thus unclear how their critical behavior is related to universality classes of known quantum and thermal phase transitions. We will discuss
this question in the case of the Dicke model realized by means of ultracold
atom gases strongly coupled to the electromagnetic radiation field of an optical resonator. We will show that the critical exponent of the recently observed
self-organization quantum phase transition is determined by the spectral density function of the reservoir and has a continuously tunable value.
43
Posters
Time-domain interferometry with nanoparticles
Nadine Dörre
University of Vienna
Boltzmanngasse 5, 1090 Wien, Austria
nadine.doerre@univie.ac.at
The wave/particle duality of matter is one of the fundamental and most intriguing concepts in quantum physics. De Broglie interferometers allow testing the superposition principle for mesoscopic objects, such as large clusters
and molecules. They serve to establish new bounds on theoretical predictions
that modify standard quantum mechanics and are interesting for measuring
molecular properties.
We discuss the principle of a time domain matter-wave interferometer for
nanoparticles which uses pulsed optical gratings and show in particular how
photo-fragmentation can used for beam-splitting. We further discuss our efforts towards and possible scenarios for breaking mass records in nanoparticle
interferometry with the aim of testing the validity of quantum theory on large
complexity scales.
Towards an optical phase shift based on Rydberg blockade
Stephan Dürr
Max-Planck Institute for Quantum Optics
Hans-Kopfermann-Str. 1, 85748 Garching, Germany
stephan.duerr@mpq.mpg.de
Controlling the interaction between single photons is important for quantum
information technology. Recently we demonstrated that an opaque medium
in which single photons are converted into stationary Rydberg excitations
can be used to control the transmission of a subsequent light pulse by using
electromagnetically induced transparency. Manipulation of coherent superpositions requires, however, non-dissipative interactions that only affect the
phase of the light. In this work we report on our recent progress towards realizing controlled phase shifts of single photons. We store photons in highly
exited Rydberg states which changes the refractive properties of the medium
due to Rydberg blockade. A subsequent light pulse will thus experience a
significant phase shift.
44
Posters
Manipulating High-Dimensional Orbital-Angular-Momentum
Entanglement
Manuel Erhard
IQOQI
Boltzmanngasse 3, 1090 Wien, Austria
manuel.erhard@univie.ac.at
We discuss the development of a interferometric beam splitter that splits light
based on the two-dimensional parity of its spatial mode structure. We demonstrate a near-unit sorting efficiency of classical light as well as single photons
carrying orbital angular momentum (OAM). This device is implemented in
a double Sagnac configuration that allows stable operation over several days.
This capability is crucial for its use in high-dimensional multi-photon experiments as an OAM parity beam splitter that mixes high-dimensionally
entangled photons from two independent nonlinear crystals.
Demonstration of the reversed dissipation regime in cavity
electro-mechanics
Alexey Feofanov
EPFL (Swiss Federal Institute of Technology in Lausanne)
EPFL-SB-ICMP-LPQM, 1015 Lausanne, Switzerland
alexey.feofanov@epfl.ch
Cavity optomechanical phenomena, such as cooling, amplification or optomechanically induced transparency, emerge due to a strong imbalance in the dissipation rates of the parametrically coupled electromagnetic and mechanical
resonators. Here we explore experimentally for the first time the reversed dissipation regime where the mechanical energy relaxation rate exceeds the energy decay rate of the electromagnetic cavity. We demonstrate optomechanically induced modifications of the microwave cavity resonance frequency and
decay rate as well as mechanically-induced amplification of the electromagnetic mode and self-sustained oscillations (maser action) with high spectral
purity of emitted microwave tone.
45
Posters
Interferometric laser cooling of atomic rubidium
Tim Freegarde
University of Southampton
School of Physics & Astronomy, SO20 6AG Highfield, Southampton, UK
timf@soton.ac.uk
When the beamsplitters of an atom interferometer change the atom’s momentum, the difference in kinetic energy between the coupled states gives a
velocity dependence to the interferometric phase. The interferometer can be
used not only to determine the atomic velocity, but also to impart a velocitydependent impulse which can cool a cloud of atoms. We report the 1-D
cooling of 85Rb atoms using a velocity-dependent optical force based upon
Ramsey matter-wave interferometry. Using stimulated Raman transitions between ground hyperfine states, 12 cycles of the interferometer sequence cool
a freely moving atom cloud from 21 to 3 µK. This pulsed analogue of c-w
Doppler cooling is effective down to the recoil limit, and will be more suitable
for species that lack a closed radiative transition.
46
Posters
Quantum decoherence of a single-ion qubit induced by single
optical photons
Konstantin Friebe
Experimentalphysik Innsbruck
Technikerstr. 25/4, 6020 Innsbruck, Austria
Konstantin.Friebe@uibk.ac.at
Quantum measurement is based on the interaction between a quantum object and a meter entangled with the object. While the information stored in
the object is being extracted by the interaction, the measurement leads to
decoherence of the object due to the intrinsic quantum fluctuations of the
meter. Here, we report the observation of measurement-induced dephasing
of a single-ion qubit with single optical photons. We employ a single 4 0Ca+
ion that is dispersively coupled to a high-finesse cavity. The cavity is driven
by a weak laser field to populate the cavity with mean photon numbers up
to five. Spectroscopy is performed on the 729 nm qubit transition to identify
the shift and broadening of the atomic energy levels. The information stored
in the qubit is extracted by photons escaping the cavity, which, in turn, leads
to dephasing of the qubit owing to photon-number fluctuations. This measurement represents the first demonstration of such quantum decoherence
effects in the optical domain. Furthermore, heterodyne measurements of the
cavity output photons will make it possible to probe quantum trajectories of
the qubit nondestructively.
47
Posters
Fermi-Bose Mixture of 6Li and 41K
Isabella Fritsche
Institut for Experimental Physics, University of Innsbruck
Technikerstraße 25, 6020 Innsbruck, Austria
Isabella.Fritsche@uibk.ac.at
We report on the production of a 41K Bose-Einstein condensate (BEC) immersed in a degenerate two-component 6Li Fermi sea. After evaporation in
an optical dipole trap, we obtain 104 41K atoms with a 33% BEC fraction
and a Fermi sea of 105 6Li atoms with a T /T F ≈ 0.1 This facilitates the
study of the collective modes of a mass-imbalanced mixture of two coupled
superfluids. Using loss spectroscopy, we observe the 335.8G Feshbach resonance, which is comparable to the one between 6Li and the fermionic 40K
isotope. We exploited the latter in previous studies on the quantum manybody dynamics of a Fermi impurity in a Fermi sea. Investigating interacting
bosonic impurities complements this work and enables the direct comparison
of the role of quantum statistics for bosonic/fermionic impurities.
48
Posters
Superfluidity of light : semiconductor microcavities and
propagation geometry
Quentin Glorieux
Laboratoire Kastler Brossel
4 Place Jussieu, 75252 Paris Cedex 5, France
quentin.glorieux@lkb.upmc.fr
Historically, research in many body-physics deals with massive material particules. It is known since the early days of quantum mechanics, that photons
in a box can be interpreted as a massless Bose gas of non-interacting particules. Recently, it has been realized that under suitable circumstances photons
can acquire an effective mass and will behave as a quantum fluid of light with
photon-photon interactions.
Experimental demonstrations of superfluidity and other quantum hydrodynamical effects will be presented in a confined geometry using semi-conductor
planar micro-cavities.
An alternative to the confined geometry will also be introduced: the use of
a monochromatic light field propagating in a non-linear medium showing an
intensity dependent an intensity dependent refractive index.
Enhanced Nonlinearity in an Atom-Driven Cavity QED System
Christoph Hamsen
Max-Planck-Institute of Quantum Optics
Hans-Kopfermann-Str. 1, 85748 Garching bei München, Germany
christoph.hamsen@mpq.mpg.de
Optical nonlinearities at the single- to few-photon level are essential to quantum optics. An atom strongly coupled to the light field of an optical cavity provides such nonlinearity. Here we investigate a cavity QED system
where the coherent drive resonantly excites the emitter. Compared to the
cavity-driven case, we expect an enhanced nonlinearity since the transition
elements from the first to higher Jaynes-Cummings manifolds are reduced.
This has distinct implications on the photon statistics of the cavity emission,
as demonstrated experimentally: Driving the emitter on the normal modes
yields an improved photon-blockade effect. In contrast, driving to the second
manifold shows a novel photon-concatenation effect reflecting the internal
dynamics of the system.
49
Posters
Dark energy search using atom interferometry
Philipp Haslinger
University of California, Berkeley
Department of Physics, 311 Le Conte Hall MS 7300, 94720 Berkeley, USA
haslinger@berkeley.edu
If dark energy, which drives the accelerated expansion of the universe, consists
of a light scalar field it might be detectable as a "fifth force" between normalmatter objects. In order to be consistent with cosmological observation and
laboratory experiments, some leading theories use a screening mechanism to
suppress this interaction. However, atom-interferometry presents a tool to
reduce this screening [1] and has allowed us to place tight constraints on a
certain class of these theories, the so-called chameleon models [2]. Recent
modifications to our cavity-enhanced atom interferometer have improved the
sensitivity by a hundredfold and we expect new results soon.
[1] C. Burrage et al., J. Cosmol. Astropart. Phys. 2015, 042 (2015).
[2] P. Hamilton et al., Science 349, 849 (2015).
Non-staggered magnetic flux in optical lattices using
multi-frequency light
Gediminas Juzeliunas
Vilnius University
A. Gostatuto 12, LT01108 Vilnius, Lithuania
gediminas.juzeliunas@tfai.vu.lt
We explore a novel way of creating a non-staggered magnetic flux for ultracold atoms by using a properly chosen periodic sequence of counter-propagating
laser pulses representing a multi-frequency perturbation. The laser fields
drive optical transitions between a pair of atomic internal states. The energies of the two internal states have opposite gradients in one spatial direction,
while the multi-frequency driving radiation propagates in a direction perpendicular to the energy gradient. This effectively creates a square optical lattice
affected by a non-staggered magnetic flux. The topological properties of such
a lattice have been explored.
50
Posters
Three photon energy-time entanglement
Thomas Kauten
Institut für Experimentalphysik
Technikerstraße 25, 6020 Innsbruck, Austria
thomas.kauten@uibk.ac.at
Creating entangled photon pairs is a long known and widely used technique in
modern quantum optics. Those photon pairs are used for various applications
such as quantum cryptography and optical quantum computation. For some
application it would be useful to have more than two photons entangled with
each other. We developed a scheme to create energy-time entangled photon
triplets from a cascaded parametric down conversion source. Our source creates approximately 2000 entangled photon triplets per hour. We analyze the
photon triplets with three imbalanced Mach-Zehnder interferometers where
we were able to observe higher order correlations in the triplet rate. In order
to prove entanglement we try to violate Mermin’s inequality, the generalized
Bell inequality for more than two particles.
Universal sign-control of coupling in tight-binding lattices
Robert Keil
Institut for Experimental Physics
Technikerstraße 25, 6020 Innsbruck, Austria
robert.keil@uibk.ac.at
We present a method of locally inverting the sign of the coupling term in
tight-binding systems, by means of inserting an ancillary site and eigenmode
matching of the resulting vertex triplet. Our technique can be universally
applied to all lattice configurations and physical platforms, as long as individual sites can be detuned. We experimentally verify this scheme in photonic
waveguide lattices and confirm the inverted sign of the coupling by interferometric measurements. Based on these findings, we demonstrate how such
universal sign-flipped coupling links can be embedded into extended lattice
structures to impose arbitrary Z2-gauge transformations. This opens a new
avenue for investigations on topological effects arising from magnetic fields
with aperiodic flux patterns or disorder.
51
Posters
Unified nonclassicality criteria and continuous sampling
Semjon Köhnke
University of Rostock
Ulmenstr. 1, 18057 Rostock, Germany
semjon.koehnke@uni-rostock.de
A number of nonclassicality criteria have been formulated to certify quantum features of states. One hierarchy is based on Bochner’s theorem and the
characteristic function of the Glauber-Sudarshan representation (P function).
Another hierarchy is formulated in terms of the matrix of moments. We combine the advantages of both, resulting in a generalization of Bochner’s theorem. For applications of the generalized nonclassicality probes, we provide
direct sampling formulas for balanced homodyne detection. Furthermore we
present a continuous phase sampling technique. In contrast to discrete phaselocked measurements, the continuous sampling of a regularized P function
allows an unconditional verification of nonclassicality, as we demonstrate for
the phase-sensitive squeezed vacuum state.
Optimized geometries for future generation optical lattice clocks
Sebastian Krämer
Institute for Theoretical Physics
Technikerstrasse 21a, 6020 Innsbruck, Austria
sebastian.kraemer@uibk.ac.at
Atoms deeply trapped in magic wavelength optical lattices provide a Dopplerand collision-free dense ensemble of quantum emitters ideal for high precision spectroscopy and they are the basis of some of the best optical atomic
clocks to date. However, despite their minute optical dipole moments the
inherent long range dipole-dipole interactions in such lattices still generate
line shifts, dephasing and modified decay. We show that in a perfectly filled
lattice line shifts and decay are resonantly enhanced depending on the lattice
constant and geometry. Potentially, this yields clock shifts of many atomic
linewidths and reduces the measurement By optimizing the lattice geometry,
such collective effects can be tailored to yield zero effective shifts and prolong dipole lifetimes beyond the single atom decay. In particular, we identify
dense 2D hexagonal or square lattices as most promising configurations for
an accuracy and precision well below the independent ensemble limit. This
geometry should also be an ideal basis for related applications such as superradiant lasers, precision magnetometry or long lived quantum memories.
52
Posters
Automated Search for new Quantum Experiments
Mario Krenn
University Vienna
Boltzmanngasse 5, 1090 Vienna, Austria
mario.krenn@univie.ac.at
Quantum mechanics predicts a number of at first sight counterintuitive phenomena. It is therefore a question whether our intuition is the best way to find
new experiments. Here we report the development of a computer algorithm
which is able to find new experimental implementations for the creation and
manipulation of complex quantum states. And indeed, the discovered experiments extensively use unfamiliar and asymmetric techniques which are
challenging to understand intuitively. The results range from the first implementation of a high-dimensional Greenberger-Horne-Zeilinger (GHZ) state,
to new types of high-dimensional cyclic transformations. The algorithm autonomously learns from solutions for simpler systems, which significantly
speeds up the discovery rate of more complex experiments.
Correlation spreading in spin systems after a quench
Carlo Krimphoff
ITP, Uni Innsbruck
Technikerstraße 21a, 6020 Innsbruck, Austria
carlo.krimphoff@uibk.ac.at
We numerically investigate the time evolution of the correlation density matrix and other correlation measures after a quantum quench in various one
dimensional spin systems. For integrable systems, dynamics is expected to
be dominated by linear quasiparticle propagation with light cones showing
algebraic decay. However in the non-integrable case, quasiparticle scattering
is expected to lead to an exponential decay and a hydrodynamical propagation pattern. Our goal is to quantify the transition of these two pictures,
when performing quenches to different non-integrable systems.
53
Posters
Single-photon Michelson Fringes from Entangled Photon Pairs
Mayukh Lahiri
IQOQI, University of Vienna
Boltzmanngasse 3, 1090 Wien, Austria
mayukh.lahiri@univie.ac.at
We observe a novel single-photon interference pattern that resembles Michelson fringes but has some remarkable properties. We use non-degenerate entangled photon pairs (signal and idler) created by spontaneous parametric
down-conversion at two spatially separated nonlinear crystals. The fringes
are obtained by superposing the two beams of signal photons from the crystals, while the idler beams are aligned to induce coherence between the signal
beams. If the phase is modulated using the idler photons, wavelengths of both
signal and idler characterize the fringe spacing. The visibility of the fringes
decreases when the momentum correlation between the photons of each pair
is reduced. Our results show that the fringes can be created only if the photons of each pair are momentum-correlated.
Gravity gradiometer
Mehdi Langlois
SYRTE
61 avenue de l’Observatoire, 75014 Paris, France
mehdi.langlois@obspm.fr
The principle of this experiment is to measure the Earth gravity gradient
by atomic interferometry. The interferometer is realised on two atomic cloud
with the same laser. By subtracting the phases of the two interferometers we
can extract the gravity gradient and reject common mode phase fluctuations.
The atoms are trap and cool on atomic chips by a magneto-optical trap
and evaporative cooling. After that we launch them with a Bloch elevator
in a tube and we realise the interferometer with large momentum transfer
beamsplitter. It allows to reach large separations between the two arms of
the interferometer,
and increase the sensitivity of the interferometer up to a
√
−11 −2
few 10 s / Hz.
54
Posters
Quantum decoherence of a single-ion qubit induced by single
optical photons
Moonjoo Lee
Experimentalphysik Innsbruck
Technikerstr. 25/4, 6020 Innsbruck, Austria
moonjoo.lee@uibk.ac.at
Quantum measurement is based on the interaction between a quantum object and a meter entangled with the object. While the information stored in
the object is being extracted by the interaction, the measurement leads to
decoherence of the object due to the intrinsic quantum fluctuations of the
meter. Here, we report the observation of measurement-induced dephasing
of a single-ion qubit with single optical photons. We employ a single 40Ca+
ion that is dispersively coupled to a high-finesse cavity. The cavity is driven
by a weak laser field to populate the cavity with mean photon numbers up
to five. Spectroscopy is performed on the 729 nm qubit transition to identify
the shift and broadening of the atomic energy levels. The information stored
in the qubit is extracted by photons escaping the cavity, which, in turn, leads
to dephasing of the qubit owing to photon-number fluctuations. This measurement represents the first demonstration of such quantum decoherence
effects in the optical domain. Furthermore, heterodyne measurements of the
cavity output photons will make it possible to probe quantum trajectories of
the qubit nondestructively.
Rotation of quantum impurities in the presence of a many-body
environment
Mikhail Lemeshko
IST Austria
Am Campus 1, 3400 Klosterneuburg, Austria
mikhail.lemeshko@ist.ac.at
We present the first systematic treatment of quantum rotation coupled to
a many-particle environment. We approach the problem by introducing the
quasiparticle concept of an "angulon" - a quantum rotor dressed by a quantum field and reveal its properties using a combination of variational and
diagrammatic techniques. The theory can be applied to a wide range of systems described by the angular momentum algebra, from Rydberg atoms immersed into BECs, to cold molecules solvated in helium droplets, to ultracold
molecular ions.
55
Posters
Coherent interaction of a Bose-Einstein condensate with two
crossed cavity modes
Julian Leonard
ETH Zürich
Otto-Stern-Weg 1, 8093 Zürich, Switzerland
leonard@phys.ethz.ch
Coupling a quantum gas to the field of a single high-finesse cavity gives rise
to interactions of infinite range between the atoms, which can create a selforganized state when exceeding a critical strength. It is desirable to tune
range and directionality of these interactions, which enables explorations of
more complex self-organized states or quantum soft matter physics, such as
superfluid glasses and associative memory. However, this requires extending
the one-cavity system to higher dimensions. We report on the realization
of such an extended system, involving a Bose-Einstein condensate coupled
to two crossed cavities modes. This already allows to spatially shape the
interactions, leading to multiple new crystalline phases, e.g. with hexagonal,
triangular or stripe order.
Fermi-Bose Mixture of 6Li and 41K
Rianne Lous
IQOQI and Institute for Experimental Physics
Technikerstrasse 21a, 6020 Innsbruck, Austria
rianne.lous@uibk.ac.at
We report on the production of a 41K Bose-Einstein condensate (BEC) immersed in a degenerate two-component 6Li Fermi sea. After evaporation in
an optical dipole trap, we obtain 104 41K atoms with a 33% BEC fraction
and a Fermi sea of 105 6Li atoms with a T /T F ≈ 0.1 This facilitates the
study of the collective modes of a mass-imbalanced mixture of two coupled
superfluids. Using loss spectroscopy, we observe the 335.8G Feshbach resonance, which is comparable to the one between 6Li and the fermionic 40K
isotope. We exploited the latter in previous studies on the quantum manybody dynamics of a Fermi impurity in a Fermi sea. Investigating interacting
bosonic impurities complements this work and enables the direct comparison
of the role of quantum statistics for bosonic/fermionic impurities.
56
Posters
Multi-photon entanglement in high dimensions
Mehul Malik
IQOQI
Boltzmanngasse 3, 1090 Vienna, Austria
mehul.malik@univie.ac.at
Forming the backbone of quantum technologies today, entanglement has been
demonstrated in physical systems as diverse as photons, ions, and superconducting circuits. While steadily pushing the boundary of the number of
particles entangled, these experiments have remained in a two-dimensional
space for each particle. Here we show the experimental generation of the
first multi-photon entangled state where both—the number of particles and
dimensions—are greater than two. Two photons in our state reside in a threedimensional space, while the third lives in two dimensions. This asymmetric entanglement structure only appears in multi-particle entangled states
with d > 2. Our method relies on combining two pairs of photons, highdimensionally entangled in their orbital angular momentum. Additionally,
we show how this state enables a new type of "layered" quantum communication protocol. Entangled states such as these serve as a manifestation of
the complex dance of correlations that can exist within quantum mechanics.
(Malik et al, arXiv:1509.02561, (2015))
57
Posters
Controlling many-body tunneling dynamics in a strongly
correlated quantum gas
Florian Meinert
Innsbruck
Technikerstraße 25, 6020 Innsbruck, Austria
florian.meinert@uibk.ac.at
Atomic gases at ultralow temperatures prepared in optical lattice potentials
provide an exquisite platform to study many-body quantum systems out of
equilibrium. Moreover, system parameters can be coherently controlled via
periodic driving as has been demonstrated for e.g. the single-particle tunneling amplitude. Here, we present a series of experiments in the context of the
Bose-Hubbard model for which we independently control the tunneling rate
J and the on-site interaction energy U. For 1D chains of bosons prepared
in a Mott insulator and subject to a tilt E, we study correlated tunneling dynamics between neighboring lattice sites (and beyond), and identify
the role of bond-charge interactions in modifying the overall tunneling rate,
i.e. giving rise to a tunneling rate that depends on the local site occupation in the lattice. We then demonstrate the controlled implementation of
such occupation-dependent tunneling in the framework of Floquet theory
via periodic modulation of interactions. This opens a new platform for the
exploration of phenomena in Hubbard models with occupation-dependent
hopping, including the possibility of dynamical synthetic gauge fields.
Coherent controlization using transmon qubits
Alexey Melnikov
Institute for Theoretical Physics, University of Innsbruck
Technikerstraße 21a, 6020 Innsbruck, Austria
alexey.melnikov@uibk.ac.at
Coherent controlization is a process by which priori unspecified (or unknown)
operations on subsystems are coherently conditioned on the state of a control qubit. The practical realization of coherent controlization requires an
auxiliary system in addition to the control and target qubits. However, the
details of the implementation depend on the nature of the ancilla system
and the type of qubit used. Here, we propose a method that allows coherent
controlization in a register of superconducting transmon qubits coupled to
an auxiliary microwave resonator.
58
Posters
The equation of state of a weakly interating 3D Bose gas
Carmelo Mordini
BEC Center – University of Trento
Via Sommarive 14, 38123 Povo - Trento, Italy
carmelo.mordini@unitn.it
We report on the progress towards the measurement of the equation of state
of a homogeneous 3D interacting Bose gas, focusing on the effects of meanfield interactions on the chemical potential across the transition. While the
topic has been widely discussed, yet no direct measurement was reported so
far. The physics of uniform gases is studied in a trapped sample through the
Local Density Approximation. We developed a new data acquisition technique based on a sequence of partial extractions of fractions of the sample
through an output coupling mechanism and the reconstruction of the original
spatial profile. This allows for the extraction of the in-situ, column-integrated
density profile of the partially condensed sample, in the full range, without
saturation effects on the CCD camera.
Quantumness Quantification
Melanie Mraz
University of Rostock
Albert-Einstein-Str. 23, 18057 Rostock, Germany
melanie.mraz@uni-rostock.de
To study the amount of nonclassicality, we propose a degree of nonclassicality being a nonclassicality measure. It is determined by the decomposition of
a quantum state into superpositions of coherent states. The more quantum
superpositions of coherent states are needed, the more quantum interferences
arise. A method for such a decomposition of quantum states is presented theoretically. Following this approach the next step is to apply this measure to
an experiment. But how can we extract the information necessary to estimate the amount of quantumness in our system? Therefore pattern functions
are used to reconstruct a density matrix in coherent state basis. Using this
method we will try to witness the amount of nonclassicality in our system.
59
Posters
Dissipative quantum phase transitions in cavity QED
David Nagy
Wigner Research Centre of the Hungarian Academy of Sciences
29-33 Konkoly-Thege M. Street, 1121 Budapest, Hungary
Nagy.David@wigner.mta.hu
A laser-driven Bose-Einstein condensate interacting with the field of a highfinesse optical cavity proves to be a versatile simulation tool, which helps us
understand quantum phase transitions in driven-dissipative systems [PRA 84,
043637 (2011)]. The cavity photon loss inhibits the observation of the superradiant quantum phase transition in the ground state. Instead, a dissipative
phase transition takes place in the steady state. Moreover, the atom field is
also subjected to dissipative decay that originates from Landau- and Beliaevtype scattering processes [PRA 89, 051601 (2014)]. This system serves as a
generic example that exhibits quantum criticality with dissipation to unconventional reservoirs having non-trivial noise spectrum [PRL 115, 043601
(2015)].
Hybrid thermo-mechanical machines powered by quantum
non-thermal baths
Wolfgang Niedenzu
Weizmann Institute of Science
234 Herzl Street, 7610001 Rehovot, Israel
Wolfgang.Niedenzu@uibk.ac.at
Diverse models of engines energised by quantum-coherent, hence non-thermal,
baths allow the engine efficiency to transgress the standard thermodynamic
Carnot bound. These transgressions call for an elucidation of their underlying mechanism. Here we show that non-thermal baths may impart not only
heat, but also mechanical work to the machine. Hence, the Carnot bound is
inapplicable to such a hybrid machine. Intriguingly, it may exhibit dual action, concurrently as engine and refrigerator, with up to 100% efficiency. The
general criteria for their quantumness are revealed. We conclude that even
when these machines are quantum or unconventional in their performance,
they still abide by the traditional principles of thermodynamics.
60
Posters
Towards strong ion-photon coupling in an ion-trap fibercavity
apparatus
Florian Ong
Universität Innsbruck
Technikerstrasse 25/4, 6020 Innsbruck, Austria
florian.ong@uibk.ac.at
A single atom coupled to an optical cavity can be used as a coherent quantum
interface between stationary and flying qubits in a quantum network. Using
fiber-based cavities, it may be possible to reach the strong coupling regime of
cavity QED with a single trapped ion. This regime would enhance the fidelity
and efficiency of protocols useful for quantum communication. The challenge
of integrating fiber cavities with ion traps is that the dielectric fibers should
be far enough from the ions so that they do not significantly alter the trap
potential. Using the CO2-laser ablation technique, we have built fiber cavities
with finesses up to 70,000 at 854nm and at a length of 550um. We will report
on the integration and interplay of such a fiber cavity with a calcium ion
stored in a Paul trap.
Twisting tensor and spin squeezing
Tomas Opatrny
Palacky University Olomouc
17. listopadu 12, 77146 Olomouc, Czech Republic
opatrny@optics.upol.cz
A unified tensor description of quadratic spin squeezing interactions is proposed, covering the single- and two-axis twisting as two special cases of a
general scheme [PRA 91, 053826 (2015)]. Equations of motion of the first
two moments are derived and conditions for the fastest squeezing generation
are found. The optimum rate of squeezing generation is proportional to the
difference between the largest and the smallest eigenvalues of the twisting
tensor. Examples of possible experimental realization are proposed in the
form of a cascaded optical interferometer with Kerr nonlinear media, and of
a toroidal Bose-Einstein condensate with spatially modulated nonlinearity
[PRA 91, 053612 (2015)].
61
Posters
Spontaneous crystallization of light and ultracold atoms
Stefan Ostermann
Institute for Theoretical Physics, University of Innsbruck
Technikerstraße 21a, 6020 Innsbruck, Austria
stefan.ostermann@uibk.ac.at
Coherent scattering of light from ultracold atoms involves an exchange of energy and momentum introducing a wealth of non-linear dynamical phenomena. As a prominent example particles can spontaneously form stationary periodic configurations which simultaneously maximize the light scattering and
minimize the atomic potential energy in the emerging optical lattice. Here
we study a regime of periodic pattern formation for a BEC in free space,
driven by far off-resonant counterpropagating and non-interfering lasers of
orthogonal polarization. In this case, no spatial light modes are preselected
by any boundary conditions and the transition from homogeneous to periodic
order amounts to a crystallization of both light and ultracold atoms breaking
a continuous symmetry. In the crystallized state the BEC acquires a phase
similar to a supersolid with an emergent intrinsic length scale whereas the
light-field forms an optical lattice allowing phononic excitations. The studied
system constitutes a novel configuration allowing the simulation of synthetic
solid state systems with ultracold atoms including long-range phonon dynamics.
Trapping ions on two generations of surface ion trap chips
Baoquan Ou
Department of Physics, Science College, NUDT
109 DeYa Road, 410000 Changsha City, China
bqou@nudt.edu.cn
The first and the second generation surface ion trap chips built in our group
and the ion trapping experiments are reportted. The Gen I surface trap consisted of five gold platted electrodes on glass substrate(SiO2), all the electrodes are distributed symmetrically , and ions are trapped 140 um above the
surface. The Gen II surface trap are built on standard PCB, five electrodes
are distributed asymmetrically, and the ions are trapped 570um above the
surface. Both surface traps are suffered heavily by heating effects, we measure
the life-time of the trapped ions and discuss the probale heating mechanics,
and the Gen III cryogenic ion trap is under constructted.
62
Posters
Experimental realization of stimulated Raman adiabatic passage
in a transmon
Sorin Paraoanu
Department of Applied Physics, Aalto University
Puumiehenkuja 2B,P.O. BOX 1510, FI-00076 AALTO Espoo, Finland
sorin.paraoanu@aalto.fi
In recent years, standard quantum-optics effects have been observed with
superconducting circuits. Our results in Helsinki include the Autler-Townes
effect, motional narrowing, Landau-Zener interference in the strong nonadiabatic regime, the dynamical Casimir effect, and the STIRAP protocol.
A fundamental prediction of quantum field theory is the existence of vacuum fluctuations. Here I will present an experiment demonstrating how the
vacuum fluctuations of a resonant superconducting circuit can be harnessed
to produce quantum coherence by employing a double parametric pumping
scheme. The existence of these correlations is a consequence of absence of
which-color information and it opens the prospect of realizing cluster states
in superconducting circuits.
The adiabatic manipulation of quantum states is a powerful technique from
quantum optics and atomic physics. Our previous work on the Autler-Townes
effect in superconducting phase qutrits [1], on Stueckelberg interference [2],
and on the effect of motional averaging in transmons [3] has added up evidence that superconducting circuits truly behave as controllable artificial
atoms. Here we benchmark the stimulated Raman adiabatic passage process
for circuit quantum electrodynamics, by using the first three levels of a transmon qubit [4].
To realize this coherent transfer, we use two adiabatic Gaussian-shaped control microwave pulses coupled to the first and the second transition. In this
ladder con guration, we measure a population transfer efficiency above 80%
between the ground state and the second excited state. The advantage of
this technique is robustness against errors in the timing of the control pulses.
By doing quantum tomography at successive moments during the Raman
pulses, we investigate the transfer of the population in time-domain. We also
show that this protocol can be reversed by applying a third adiabatic pulse.
Furthermore, we study the e ffect of applying the adiabatic Raman sequence
to a superposition between the ground and the first excited state, and we
present experimental results for the case of a quasi-degenerate intermediate
level. The result is one step towards the realization of holonomic quantum
computing and quantum simulators with superconducting circuits [5].
[1] Mika A. Sillanpää, et. al., Phys. Rev. Lett. 103, (2009) 193601; Jian Li
63
Posters
et. al., Phys. Rev. B 84, (2011) 104527; Jian Li et. al. , Sci. Rep. 2, (2012)45;
[2] M.P. Silveri, K.S. Kumar, J. Tuorila, J. Li, A. Veps""al""ainen, E.V.
Thuneberg, G.S. Paraoanu, New J. Phys. 17 (2015) 043058.
[3] Jian Li, M. P. Silveri, K. S. Kumar, J.-M. Pirkkalainen, A. Vepsäläinen,
W. C. Chien, J. Tuorila, M. A. Sillanpää, P. J. Hakonen, E. V. Thuneberg,
G. S. Paraoanu, Nat. Commun. 4, 1420 (2013);
[4] K. S. Kumar, A. Vepsalainen, S. Danilin, G. S. Paraoanu, arXiv:1508.02981.
[5] G. S. Paraoanu, Recent progress in quantum simulation using superconducting circuits, J. Low. Temp. Phys. 175, (2014) 633-654.
Single-shot, complete characterization of a single-photon state
Sergey Polyakov
NIST
100 Bureau Dr., 20877 Gaithersburg, USA
spoly@nist.gov
We simultaneously determine the single photon purity, photon indistinguishability, and reconstruct higher-order statistical distribution of photon-number
states of a light source, characterizations that up to now have used multiple sequential measurements. This new method takes advantage of photonnumber resolved detection, and extracts more information about the source
per one measurement than a conventional method for any single-photon state.
We assess the measurement efficiency of available characterization methods
and find the most advantageous strategy as a function of light source parameters. For demonstration, we characterize the light from a single quantum
dot. The platform can be used as a metrology testbed, or as an elementary
block of a boson sampling protocol.
64
Posters
Symmetry-protected topologically ordered states for universal
quantum computation
Hendrik Poulsen Nautrup
Institute for Theoretical Physics
Technikerstraße 21a, 6020 Innsbruck, Austria
h.poulsennautrup@gmail.com
Measurement-based quantum computation is a model for quantum information processing utilizing local measurements on suitably entangled resource
states for the implementation of quantum gates. A complete characterization
for universal resource states is still missing. It has been shown that symmetryprotected topological order in one dimension can be exploited for the protection of certain quantum gates in measurement-based quantum computation.
I will illustrate that the two-dimensional plaquette states on arbitrary lattices
exhibit nontrivial symmetry-protected topological order in terms of symmetry fractionalization and that they are universal resource states for quantum
computation.
Excitations in Dense Bose Gases of Tilted Dipoles in Coupled
2D-Layers
Michael Rader
Institute for Theoretical Physics
Technikerstr. 21a, 6020 Innsbruck, Austria
michael.rader@uibk.ac.at
In this work excitations in strongly interacting dipolar Bose gases, that are
trapped in coupled 2D-layers, are investigated. Equations of motion are derived using a least-action principle equivalent to the Schrödinger equation.
We solve the equations of motion to determine the density-density linear
response matrix in a very general way for inhomogeneous multi-component
systems. This result is a generalisation of the work of Clements et al. [PRB
53, 12253 (1996)] for multi-component systems. We discuss how the general
formalism can be applied to homogeneous systems. Based on ground state
results, obtained with the hypernetted-chain Euler-Lagrange method, numerical evaluations of the density-density response matrix are performed for oneand two-layer systems, that have either a polarisation perpendicular to the
layers or a tilted polarisation. We find systems with tilted dipoles, that are
about to solidify in the direction orthogonal to thepolarisation of the system.
65
Posters
Quantum error correction by engineered dissipation
Florentin Reiter
Institute for Quantum Optics and Quantum Information
Technikerstr. 21a, 6020 Innsbruck, Austria
florentin.reiter@gmx.de
Performing advanced quantum information protocols in the presence of decoherence requires quantum error correcting codes. Harnessing dissipation to
correct for errors represents a conceptually different approach which allows
for features different from established approaches. We present a quantum
error correcting code based on engineered dissipation built from always-on
couplings and sources of noise. Our scheme operates in an autonomous and
continuous manner, without the need to perform measurements or unitary
operations on the system, and can be implemented using couplings which are
available in standard quantum optical systems, e.g. trapped ions.
Levitated Single-Magnetic-Domain Nanospheres in the Quantum
Regime
Cosimo Carlo Rusconi
IQOQI and UNI Innsbruck
Technikerstr. 21a, 6020 Innsbruck, Austria
cosimo.rusconi@uibk.ac.at
We propose to magnetically levitate a single-magnetic-domain nanosphere in
the vicinity of a quantum circuit. We develop the theoretical background to
describe the rich dynamics of the nanosphere in the highly prolarized regime:
tightly confined in position, nearly not rotating and with the macrospin antialigned to the magnetic field. The parameter regime for the stability of the
highly polarized regime is obtained. A magnetic on-chip set-up for cooling
the system in the quantum regime is discussed.
66
Posters
Single shot simulations of dynamic quantum many-body systems
Kaspar Sakmann
Atominstitut, TU Wien
Stadionallee 2, 1020 Vienna, Austria
kaspar.sakmann@ati.ac.at
Single experimental shots of ultracold quantum gases sample the manyparticle probability distribution. In some cases single shots could be successfully simulated from a given many-body wave function [1-4]. However,
for realistic time-dependent many-body dynamics this has long been elusive.
Here, we show how single shots can be simulated from numerical solutions
of the time-dependent many-body Schr""odinger equation. Using this technique we provide first principle explanations of several many-body phenomena, including fluctuating many-body vortices, partially destructive imaging
as well as full counting distributions of center of mass fluctuations of attractive BECs.
Quantum error correction with trapped ions
Philipp Schindler
Institute for Experimental Physics
Technikerstrasse 25/4, 6020 Innsbruck, Austria
philipp.schindler@uibk.ac.at
It seems out of question that a large-scale quantum information processor
will require quantum error correction procedures to run a long quantum algorithm. In our trapped ion quantum information processor we have realized
repetitive three qubit error correction and encoded a logical qubit in a 7
qubit Color Code. Building on this, we demonstrate operations on the encoded qubit. A major milestone for quantum error correction would be a
logical qubit that outperforms the bare physical qubits in any respect. A
prerequisite for this is to model the effect of noise on the system with high
accuracy. For this, we use robust methods for characterizing the noise in our
system.
67
Posters
Quantum State Tomography for Optical Soliton Molecules
Oskar Schlettwein
University of Rostock
Albert-Einstein-Straße 24, 18059 Rostock, Germany
oskar.schlettwein@uni-rostock.de
Bright pulses in optical fibers mainly experience dispersion, the Kerr-effect
as well as (stimulated) Brillouin and Raman scattering. The scattering processes introduce phase noise which becomes important for applications at or
below the shot noise limit. In contrast to Brillouin scattering the impact of
the Raman effect on quantum states is not clear. Numerical simulation as
well as a quantum state tomographic setup for bright pulsed signals will be
presented to provide deeper insight about it. Extending our system to a two
mode quantum state tomograph will lead the way to probe correlation effects
in soliton molecules. This stable configuration of two or more DM-solitons
could provide a fruitful source for new fiber based quantum communication
application.
From the transverse field Ising model to conformal field theory in
2+1D
Michael Schuler
Institut für theoretische Physik, University of Innsbruck
Technikerstraße 21a, 6020 Innsbruck, Austria
michael.schuler@uibk.ac.at
Conformal field theories (CFTs) have been a useful tool to describe systems
at quantum critical points. Already some time ago, Cardy pointed out that
the infinite Rd can be conformally mapped to S d−1 × R. If the dimension R is
then interpreted as time direction, this means, that the energy spectrum of
an appropriate quantum Hamiltonian on S d−1 can be directly related to the
scaling dimensions of the corresponding CFT. This approach turned out to
be very successful for d = 2, where the quantum Hamiltonian is defined on a
periodic chain. For d = 3, however, Hamiltonians have to be simulated on the
geometry of a 2D sphere, where finite-size scaling turns out to be extremely
difficult. By replacing the sphere with a torus and using large-scale exact
diagonalization and quantum Monte Carlo methods, we show that the lowenergy spectrum after finite-size scaling is universal even in that case and
can serve as a fingerprint for the underlying CFT.
68
Posters
Detailed characterization of three-qubit linear optical quantum
Toffoli gate
Michal Sedlak
Institute of Physics, Slovak Academy of Sciences
Dubravska cesta 9, 845 11 Bratislava, Slovakia
michal.sedlak@savba.sk
We report on a detailed characterization of three-qubit linear optical quantum Toffoli gate by two efficient methods. The first method provides a bound
on quantum process fidelity that is determined by average output state fidelities for three partially conjugate product bases. A distinct advantage of this
approach is that only fidelities with product states need to be measured while
keeping the number of measurements much smaller than for other methods
(192 two-photon coincidences suffice). For the second method we measured
4032 different two-photon coincidences which allow us to estimate the fidelity
of the gate to be 90%. Although these data are not tomographically complete, we show that they are sufficient for a reliable reconstruction of the
quantum process matrix of the gate.
Optical tweezer
Seyedeh Sahar Seyed Hejazi
OIST Okinawa Institute of Science and Technology)
Tancha Onna-son, 1919-1 Okinawa, Japan
sahar.hejazi@oist.jp
Optical tweezer and plasmic trap of nano-particle.
69
Posters
Cavity-induced chiral states of fermionic quantum gases
Ameneh Sheikhan Soudani
University of Bonn
Nussallee 14-16, 53115 Bonn, Germany
asheikhan@uni-bonn.de
We investigate ultracold fermions placed into an optical cavity and subjected
to optical lattices which confine the atoms to ladder structures. A transverse
running-wave laser beam induces together with the cavity field a two-photon
Raman-assisted tunneling process with spatially dependent phase imprint
along the rungs of the ladders. We investigate the steady states which can
arise by the feedback mechanism between the cavity and the atoms. We find
that a spontaneous occupation of the cavity field can arise which leads to the
self-organization of an artificial magnetic field felt by the fermionic atoms.
These form a chiral insulating or chiral liquid state which carries a chiral
current. We explore the rich state diagram on different parameters of the
model.
Vacuum-Induced Quantum Brownian Motion of a Magnetic
Particle Near a Surface
Kanupriya Sinha
Institute for Quantum Optics and Quantum Information (IQOQI)
Technikerstraße 21a, 6020 Innsbruck, Austria
kanupriyasinha@gmail.com
We study the quantum Brownian motion (QBM) of a magnetic particle near a
surface as induced by its coupling to the vacuum electromagnetic (EM) field.
We derive a general QBM master equation for a magnetic particle including
its interactions with a surface via the quantum fluctuations of the vacuum
EM field. We then apply our analysis to the specific case of a superconducting
microsphere in an all magnetic on-chip setup and study the vacuum induced
decoherence of its center of mass motion and Casimir friction. Our analysis is
generally applicable to all magnetic on-chip architectures with nanomagnets
and superconducting microspheres and our results are relevant for recent
proposals on on-chip matter-wave interferometers of microspheres.
70
Posters
A trapped atom interferometer for short range forces
measurement
Cyrille Solaro
SYRTE Système de Référence Temps Espace
61 Avenue de l’Observatoire, 75014 PARIS, France
cyrille.solaro@obspm.fr
We demonstrate a trapped ultracold atom interferometer in a vertical optical lattice. For shallow depths of the lattice, stimulated Raman transitions
can be used to induce coherent transport between adjacent Wannier-Stark
states, allowing us to perform atom interferometry. This short range forces
sensor shows state of the art relative sensitivity on the Bloch frequency of
1.8 × 10−6 at 1s. Using ultracold atoms allowed reducing coupling and phase
inhomogeneities and increased the interrogation time up to several seconds
via a spin self-rephasing mechanism (ISRE) originating from particle indistinguishability. In this specific configuration, where the two partial wavepackets
are spatially separated and do not perfectly overlap, we test self-rephasing
as a function of this overlap.
71
Posters
Radiation Forces in Time-Dependent Optical Fields
Matthias Sonnleitner
School of Physics and Astronomy, University of Glasgow
Kelvin Building, Uni Glasgow, G128QQ Glasgow, UK
matthias.sonnleitner@glasgow.ac.uk
The mechanical interaction between light and atoms, molecules or nanoparticles is usually described in two terms: the dipole force, dragging particles
along the gradient of the light intensity; and the radiation pressure, pushing particles along the direction marked by the Poynting vector. However, if
some parameters of the radiation field vary in time, like in a light pulse or
an amplitude-modulated standing wave, additional force terms appear which
are not fully covered by a time-dependent dipole force or radiation pressure.
In fact, they sometimes even act against the intuitively expected forces. The
origin of these forces lies in the so called Röntgen interaction term, although
our treatment involving time-dependent fields goes beyond the usually discussed modifications regarding moving atoms. Obviously these additional
terms are very small compared to usual radiation interactions, but given the
rapid advancement of the field and proposals to use optically trapped atoms
as sensors for other weak forces, we believe it is important to study these
small terms as well. Here we present the general idea, some simple results
and possible applications for this surprising and fascinating extension to optical forces, which we believed to understand so well.
72
Posters
Chip Integrated Nano-Fiber Atom-Photon Interface
Florian Steiner
Atominstitut, TU Wien
Stadionallee 2, 6020 Vienna, Austria
fsteiner@ati.ac.at
Micro-Optics on Atom chips; The experiment concerns the combination of
two established concepts in Ultracold-Atompyhsics. The first is trapping
atoms magnetically on atom-chips in a one dimensional fashion. The second is using nanofiber based elongated cavities which are integrated close
to the chip. Together, this constitutes a unique platform to probe atomphoton interactions. The intrinsically mode-matched resonator consists of
two fiber Bragg gratings (FBG) that are being lased onto the fiber. I will
present the newest measurements which show strong coupling of atoms from
a magnetic trap to the cavity. A few exemplary applications for our system
are: Self-organization of atoms due to Bragg Scattering into the cavity mode;
Frequency selective fluorescence spectroscopy of atoms in the surface-induced
potential of the fibre; Strong nonlinear interactions between individual photons; Realizing a Photon-Transistor.
Moving single atoms
Dustin Stuart
University of Oxford
22 Nursery Close, OX3 7AG Oxford, UK
dustin.stuart@physics.ox.ac.uk
Single neutral atoms are promising candidates for qubits, which can be interfaced with high-finesse optical cavities to form quantum networks. We have
built a set of optical tweezers for trapping and moving single Rubidium atoms
within such cavities. We use a digital micromirror device (DMD) to produce
holograms of the desired arrangement of traps. The DMD has a frame rate
of 20 kHz which, when combined with fast algorithms [1], allows for rapid
reconfiguration and transport. We demonstrate trapping of up to 20 atoms
in arbitrary arrangements, and single-atom transport over a distance of 14
um with continuous laser cooling, and 5 um without.
[1] Fast algorithms for generating binary holograms - (http://arxiv.org/abs/1409.1841)
73
Posters
Appearance and disappearance of quantum correlations in
measurement-based feedback
Vivishek Sudhir
Swiss Federal Institute of Technology (EPFL)
BM 2116, Station 17, LPQM1, 1007 Lausanne, Switzerland
vivishek.sudhir@epfl.ch
We implement a measurement-based feedback protocol to cool a solid-state
mechanical oscillator to its ground state. Correlations between the oscillator
and the light used to measure it, are recorded via sideband asymmetry. As
the oscillator is cooled, the scattered sidebands become asymmetric. Further
increase in the feedback gain leads to a decrease in the asymmetry due to
amplified shot-noise dominating the error signal.
Dynamical effects in electromagnetic induced transparency
Klara Theophilo
University of Oxford
Clarendon Lab., Parks Roads, OX1 3PU Oxford, UK
asckinha@gmail.com
The electromagnetic induced transparency (EIT) is one of the most explored
effects in quantum optics research. However, the dynamical effects of EIT still
majorly uncharted. Our research focused on a better understanding of atomic
dynamics, investigating a transient interaction of cold rubidium atoms in a
Lambda EIT system,using noise correlation spectroscopy. We characterised
the system for a broad range of experimental parameter, including observations of its temporal evolution. Moreover, we developed a theoretical model
to explain our results, showing a coupling between internal and external
atomic degrees of freedom. Unraveling this feature in EIT systems was only
possible due to noise spectroscopy, highlighting the importance of exploring
techniques beyond mean intensity spectroscopy.
74
Posters
Nonlinear Quantum Optics Using Interacting Rydberg Atoms
Christoph Tresp
5. Physikalisches Institut, Universität Stuttgart
Pfaffenwaldring 57, 70569 Stuttgart, Germany
c.tresp@physik.uni-stuttgart.de
Mapping the strong interactions between Rydberg atoms in ultracold atomic
ensembles onto single photons via EIT enables realizing huge optical nonlinearities. We report the realization of a free-space single-photon transistor,
where a single gate photon controls the transmission of many source photons
[1]. We show that the gain of the transistor can be enhanced using Starktuned Förster resonances and might be suitable as a quantum device where
the gate input is retrieved after the transistor operation. We also present our
work investigating the interaction between individual polaritons coupled to
Rydberg D-states, where the anisotropy leads to state-mixing interactions
[2].
[1] H. Gorniaczyk et al: Phys. Rev. Lett. 113, 053601 (2014)
[2] C. Tresp et al: Phys. Rev. Lett 115, 083602 (2015)
Fermi-Fermi mixtures of dysprosium and potassium
Slava Tzanova
Institut for Experimental Physics, University of Innsbruck
Technikerstraße 25, 6020 Innsbruck, Austria
Slava.Tzanova@uibk.ac.at
Ultracold Fermi-Fermi mixtures with tunable interactions represent an intriguing test bed for exploring the physics of strongly interacting many-body
quantum systems and few-body quantum states. Two-species Fermi gases extend the variety of phenomena thanks to mass imbalance. This motivates us
to construct a dysprosium - potassium experiment exploiting the favorable
mass ratio of 4. The strong magnetic moment of dysprosium allows elastic
dipolar scattering between identical fermions and offers an additional degree
of freedom to our system.
75
Posters
Towards quantum nonlinearities in an intracavity Rydberg
medium
Imam Usmani
Institut d’Optique Graduate School
2 avenue augustin fresnel, 91127 palaiseau, France
imam.usmani@institutoptique.fr
The realization of a strong deterministic photon-photon interaction is a challenging task, but could enable the implementation of a two-photon phase
gate. Nonlinearities in standard media are however too weak to induce such
effects. One approach is to sent a photon in a cold atomic ensemble to temporally convert it into a dark-state polariton and use the Rydberg blockade for
a deterministic interaction. Here, our atomic cloud is placed into an optical
cavity which increases the light-matter coupling and translates a nonlinear
dispersion into a shift of the cavity resonance. We will present the intracavity nonlinear absorptions we observed, with a comparison to our theoretical
models. Then, with some improvements on the setup, we aim at observing
bunching or anti-bunching of light.
76
Posters
Internal State Coupling of a Micromechanical Resonator to an
Atomic Ensemble
Berit Vogell
IQOQI/Universität Innsbruck
Technikerstrasse 21a, 6020 Innsbruck, Austria
berit.vogell@uibk.ac.at
Combining AMO physical systems with newly developed solid state devices
into so-called hybrid quantum systems is motivated by the idea to combine
the advantages of both, AMO and solid state systems, while compensate their
disadvantages. We present two realizations of such hybrid quantum systems
that implement the coupling of a mechanical resonator, such as a micromechanical membrane, to an atomic system by coupling to the internal states
of the atoms. In the first part a hybrid quantum system consisting of a moving micromechanical resonator coupled to a spin wave of a distant atomic
ensemble of three-level atoms is discussed. The interaction of the motional
states of the mechanical oscillator to the internal states of the atomic ensemble is mediated by a polarized light field. The coupling works via translating
the phase shift caused by a displacement of the mechanical resonator into
a polarization rotation, and is enhanced by the square root of the number
of atoms. As a second hybrid system, we propose a scheme to engineer a
Jaynes-Cummings interaction between a moving membrane and the internal
degrees of freedom of a Rydberg superatom, which models an effective two
level system. Exploiting the collective enhancement of the superatom Rabi
frequency strong coupling is feasible within accessible parameter regimes.
This hybrid system provides a broad toolbox for strong coupling in an AMO
hybrid mechanical system. As an extension of a membrane-superatom inside
a cavity setup, the alternative of long distance coupling between the systems
is also discussed.
77
Posters
Photon pairs from microcavity polaritons
Zoltán Vörös
Institute for Experimental Physics
Technikerstraße 25/d, 6020 Innsbruck, Austria
zvoros@uibk.ac.at
Interacting photons can be created by dressing them with material excitations. This interaction can be the basis for producing non-classical photon
correlations, such as squeezed or entangled light. In our case, the dressed
states, called polaritons, are created by enclosing a quantum well in a λ cavity.
In this contribution, we discuss our work on photon scattering in a polariton
sample with ultralow photonic and excitonic disorder. We demonstrate, how
the photon statistics depends on a number of experimental parameters, e.g.,
excitation density, and temporal filtering, and identify a parameter range,
where quantum correlations can be observed. We also compare our experimental findings to analytical and numerical models and calculations.
Quantum information processing with long-wavelength radiation
Simon Webster
University of Sussex
Pevensey 2, Falmer Campus, BN1 9QH Brighton, UK
s.webster@sussex.ac.uk
Trapped ion quantum computation will require scaling systems to a large
number of qubits. The use of long-wavelength radiation is a powerful scaling
technology due to the ability to use a single set of global control fields to
drive an arbitrary number of gates in parallel, with ions selected for gate
operations by locally applied magnetic fields. I will report the experimental demonstration of important tools towards this end such as the demonstration of ground state cooling using long wavelength radiation and the
demonstration of a high-fidelity long-wavelength two-ion quantum gate using a quantum-engineered clock qubit with fidelity of 0.985(12). Finally, I
will present results concerning the development of ion microchips that can
be used as an architecture for such a quantum computer.
78
Posters
Optimal measurement strategies for the lifted trine states
Graeme Weir
University of Glasgow
Kelvin Building, G12 8QQ University of Glasgow, UK
g.weir.2@research.gla.ac.uk
We investigate measurement strategies for the three symmetric quantum
states which comprise the so-called lifted trine ensemble, parameterised by
a lifting angle. We then introduce a measurement which will always provide either an unambiguous outcome or an eliminatory outcome, and is thus
guaranteed to provide some degree of certainty in state discrimination. These
measurements are compared against one another using two common figures
of merit: probability of error and mutual information. We also find that this
measurement becomes unfeasible at a certain lifting angle; beyond this angle,
some inconclusive outcome which provides no information about the state is
required.
Exploiting light-shift effects for atomic magnetometry
Arne Wickenbrock
Uni Mainz
Kurfuerstenstrasse 35, 55118 Mainz, Germany
wickenbr@uni-mainz.de
We demonstrate a selection of experiments exploiting vector light shift effects for atomic magnetometry. The fictitious magnetic fields of two circular
polarized laser beams are used to transform a scalar magnetometer with fT
sensitivity to an all-optical vector magnetometer. The sensor exhibits a projected sensitivity of 12f T /Hz 1/2 and 5microrad/Hz 1/2 . A second experiment
demonstrates a novel approach to all-optical magnetometry with potential
advantages for magnetometer arrays and magnetically sensitive fundamental
physics experiments. Intensity modulation of a laser beam at the Larmor
frequency directly drives a narrow magnetic resonance in alkali vapor. As a
magnetometer the setup achieves a projected shot-noise-limited sensitivity
of 1.7f T /Hz 1/2 and measures a technical noise floor of 40f T /Hz 1/2 . These
results are essentially identical to a coil-driven scalar magnetometer using
the same setup. In a third experiment we demonstrate that the long spin
coherence time in paraffin-coated cells leads to spatial averaging of the light
shifts over the entire cell volume, which renders the averaged light shift independent, under certain approximations, of the light-intensity distribution
within the sensor cell.
79
Posters
Some improved techniques in trapped ion quantum computing
Yi Xie
National University of Defense Technology
#109 Deya Road, 86-410073 Changsha City, China
xy2004130102@163.com
We will introduce the experiment progress of Ion trap Quantum Computing
program in National University of Defense Technology. Ground state cooling was preliminary performed on one Calcium ion trapped in a blade-trap
reaching < 0.5. Some improved techniques will also be reported. A three
steps photo-ionization experiment was performed on Calcium atoms by two
lasers containing one violet laser and one red laser in order to prevent the
UV contamination. Fluorescence revival under low magnetic field by mixed
repump lasers will also be described. We also provide a method to improve
the optical pump efficiency despite the laser polarization is not pure enough.
Efimov States in Lithium-Rubidium-Mixtures
Claus Zimmermann
Uni Tübingen
Dürrstraße, 72070 Tübingen, Deutschland
claus.zimmermann@uni-tuebingen.de
We study collisional heating in a cold 7Li-87Rb mixture near a broad Feshbach resonance at 661 G. At the high field slope of the resonance, we find an
enhanced three-body recombination rate that we interpret as a heteronuclear
Efimov resonance. With improved Feshbach spectroscopy of two further resonances, a model for the molecular potentials has been developed that now
consistently explains all known Feshbach resonances of the various Li-Rb isotope mixtures. With this model, we determine the scattering length of the
observed Efimov state. Its value of -1870a0 supports the currently discussed
assumption of universality of the three-body parameter also in heteronuclear
mixtures.
80
Posters
Single Photon Source based on Room Temperature Vapor Cells
Michael Zugenmaier
Niels Bohr Institute, University of Copenhagen
Blegdamsvej 17, 2100 Kobenhavn, Denmark
zugenmaier@nbi.ku.dk
The DLCZ protocol for long distance quantum communication is based on the
storage of single collective excitations, superposition quantum states where
one of many indistinguishable atoms is excited. We report on the progress of
our experiment applying room temperature vapor cells to create and store
a single collective excitation. A weak laser pulse excites one of the Cesium
atoms inside the vapor. The single excitation will be heralded by the detection of a single forward-scattered photon. The paraffin-coated cell walls
preserve coherence times over milliseconds. The readout of the single excitation deterministically creates a single photon with high efficiency. Scalability
and fast reinitialization allow to combine such cells to create a quantum information network.
81
Sponsors
Sponsors
We gratefully acknowledge support from our industrial sponsors:
83
Index
Index
Asenbaum Peter, 37
Hofstetter Walter, 14
Huillery Paul, 16
Bala Prasanna Venkatesh, 37
Bancal Jean-Daniel, 38
Banuls Maria Carmen, 12
Baranov Mikhail, 38
Bertoldi Andrea, 39
Biondi Matteo, 39
Boll Martin, 40
Bostock Harry, 40
Bougas Loukourgos, 41
Brennecke Ferdinand, 41
Briant Tristan, 27
Budker Dmitry, 32
Juzeliunas Gediminas, 50
Kaiser Robin, 35
Katori Hidetoshi, 31
Kauten Thomas, 51
Keil Robert, 51
Kirchmair Gerhard, 34
Koehnke Semjon, 52
Kollar Alicia, 22
Krämer Sebastian, 52
Krenn Mario, 53
Krimphoff Carlo, 53
Kuhn Axel, 6
Calajo Giuseppe, 42
Catani Jacopo, 9
Lahiri Mayukh, 54
Landini Manuele, 21
Langlois Mehdi, 54
Lee Moonjoo, 55
Leibfried Dietrich, 18
Lemeshko Mikhail, 55
Leonard Julian, 56
Lous Rianne, 56
Dayan Barak, 29
Diorico Fritz, 42
Dittel Christoph, 43
Doerre Nadine, 44
Domokos Peter, 43
Duerr Stephan, 44
Dunjko Vedran, 35
Erhard Manuel, 45
Glorieux Quentin, 49
Gross Christian, 11
Malik Mehul, 57
Marquardt Florian, 23
Meinert Florian, 58
Mekhov Igor, 33
Melnikov Alexey, 58
Mintert Florian, 13
Mordini Carmelo, 59
Morigi Giovanna, 14
Mraz Melanie, 59
Muschik Christine, 17
Hamsen Christoph, 49
Haslinger Philipp, 50
Hemmerich Andreas, 9
Nagy David, 60
Niedenzu Wolfgang, 60
Northup Tracy, 19
Feofanov Alexey, 45
Ferrier-Barbut Igor, 10
Folman Ron, 15
Freegarde Tim, 46
Friebe Konstantin, 47
Fritsche Isabella, 48
85
Index
Ong Florian, 61
Opatrny Tomas, 61
Ostermann Stefan, 62
Ou Baoquan, 62
Solaro Cyrille, 71
Sonnleitner Matthias, 72
Steiner Florian, 73
Strack Philipp, 20
Stuart Dustin, 73
Sudhir Vivishek, 74
Paraoanu Sorin, 63
Piazza Francesco, 30
Pohl Thomas, 13
Polyakov Sergey, 64
Polzik Eugene, 5
Popescu Sandu, 33
Poulsen Nautrup Hendrik, 65
Theophilo Klara, 74
Thompson James, 24
Toermae Paeivi, 28
Tresp Christoph, 75
Tzanova Slava, 75
Rabl Peter, 32
Rader Michael, 65
Reiter Florentin, 66
Reitzenstein Stephan, 27
Rempe Gerhard, 25
Romero-Isart Oriol, 8
Rusconi Cosimo Carlo, 66
Usmani Imam, 76
Voeroes Zoltán, 78
Vogell Berit, 77
Webster Simon, 78
Weihs Gregor, 26
Weir Graeme, 79
Wengerowsky Sören, 29
Wickenbrock Arne, 79
Sakmann Kaspar, 67
Schindewolf Andreas, 7
Schindler Philipp, 67
Schlettwein Oskar, 68
Schmidt Piet, 19
Schuler Michael, 68
Schweigler Thomas, 10
Sedlak Michal, 69
Seyed Hejazi Seyedeh Sahar, 69
Sheikhan Soudani Ameneh, 70
Sinha Kanupriya, 70
Xie Yi, 80
Yao Norman, 8
Zakrzewski Jakub, 20
Zeppenfeld Martin, 34
Zimmermann Claus, 80
Zugenmaier Michael, 81
86
test