Quantum metamaterials, quantum
imaging, quantum engineering and
quantumness
Alexandre Zagoskin
Department of Physics
Loughborough University
June 1, 2015
• The fabrication and control of macroscopic artificial
quantum structures, such as qubits, qubit arrays,
quantum annealers and, recently, quantum
metamaterials, have witnessed significant progress over
the last 15 years. This was a surprisingly quick evolution
from theoretical musings to what can now be called
quantum engineering [the observation of such
phenomena even in a single superconducting device was
considered a truly challenging task in 1980. Today, we
stand at the point where existing theoretical and
computational tools become inadequate for predicting,
analysing, and simulating the behaviour of such
structures, in which quantum superposition and
entanglement are essential. Quantum metamaterials can
play an important role both as a testing ground for the
development of such new tools and as a platform for the
realization of quantum technologies 2.0.
QMM Events
• Quantum
metamaterials at:
▫ Metamaterials 2011
(Barcelona)
▫ Metamaterials 2012
(Paris)
▫ Metamaterials 2012 (St.
Petersburg)
▫ META2012 (Nanjing)
▫ Metamaterials 2013
(Bordeaux)
▫ PIERS 2013 (Taipei)
Philosophy of quantum mechanics
• Copenhagen interpretation
• Many worlds
• Environmental decoherence
▫ Quantum Darwinism
•
•
•
•
Consistent histories
Pilot wave
?
“Shut up and calculate!”
…and all that Capra
• All popularizations of quantum mechanics are
wrong
• Some are much more wrong than others
• “Amount of knowledge the ancients did not possess
was obviously very significant”
 Attributed to Mark Twain
Philosophy:
baggage train of science
• …which is necessary and useful, but should
never ever be in the lead
Copenhagen vs. Schengen
quantum-classical boundary
Qubits for quantum computing and
much, much more
Phase qubit: Allman et al., 2010
Charge qubits: Yamamoto
et al., 2003
Flux qubits: Grajcar et al.,
2006
Why now?
• Fabrication of multiqubit arrays with controlled macroscopic
quantum coherence now possible
• Current theoretical methods at their limit and new
approaches are urgently needed
• Applications (part of “quantum technologies 2.0”):
▫
▫
▫
▫
Integrated quantum limited detection and image processing
Quantum optimization
Quantum simulation
Quantum communication
D-Wave controversy
D-Wave controversy
• World’s biggest collection of qubits (current version
“Washington” has 1152 qubits, 933 operational)
• Quantum operation confirmed for 8-qubit register
• Operation consistent with both quantum and classical
models
• Decoherence time of a qubit much shorter than the
adiabatic evolution time
• How to tell whether it is quantum, and if so, is it
quantum enough?
• 3000× SNAFU
• Recent data (C. Williams at Oxford): N-qubit system
with E couplers stays within 𝑁 + 𝐸 from the ground
state – consistent with the LZ diffusion picture
How far do we get from the initial
state?
• “LZ diffusion”
 N – number of anticrossings
per energy level
Wang L, Roennow T, Boixo S, Isakov S,
Wang Z, Wecker D, et al. Comment on:
“Classical signature of quantum
annealing.” arXiv:1305.5837 (2013).
Shin S, Smith G, Smolin J, Vazirani U. How
“Quantum” is the D-Wave machine?
arXiv:1401.7087 (2014).
Grand Challenge
Quantum engineering for QT2.0
• Accommodating incompatible requirements
• Using “rule-of-thumb” estimates for
characterizing and predicting the system’s
performance and reliability
• Heuristics
• Scaling
• “Engineering is about building reliable
structures using non-reliable components”
So, what can we do with many good
enough qubits?
Metamaterials: artificial optical media
• Left-handed MMs
▫ Negative refractive index
 Superlenses
 Cloaking
• Photonic bandgap MMs
▫ Photonic crystals
• Tunable MMs
• MM antennas
N.I. Zheludev. The Road Ahead for Metamaterials.
Science 328, 582 (2010)
Quantum metamaterials:
• Artificial optical media that have the following
properties:
▫ They are composed of quantum coherent unit
elements with engineered parameters
▫ Quantum states of these elements can be
controlled
▫ The whole structure can maintain global
quantum coherence for longer than the traversal
time of a relevant electromagnetic signal
Rakhmanov, Zagoskin, Saveliev & Nori, Phys. Rev. B 77, 144507 (2008)
Quantum metamaterials: a
brave new world
• Introducing quantum degrees of
freedom opens new ways to control
light-matter interaction in artificial
structures.
▫ D. Felbacq and M. Antezza
 SPIE Newsroom, 19 June 2012
View from… META’12:
Metamaterials mature
• Researchers in the field of
metamaterials are … tackling new
topics such as quantum
metamaterials.
▫ David Pile
 Nature Photonics 6, 419 (2012)
• A quantum computer can be considered a
special case of a quantum metamaterial
QMMs from 2008 to 2014
•Theoretical proposal:
•Rakhmanov, Zagoskin, Saveliev & Nori, Phys. Rev. B 77, 144507 (2008)
•Zagoskin, Rakhmanov, Saveliev & Nori, Phys. Stat. Solidi B 246, 955 (2009)
•
(a)
(b)
Proof of principle: Astafiev, Zagoskin et al., •
Science (2010)
Experimental prototype: Macha et al. (2013)
(d)
(c)
a
1 m
I
tI
0
Is
Is
0
Non-superconducting platforms:
Atom-cavity arrays:
Quach et al.,
6 June 2011 / Vol. 19, No. 12 /
OPTICS EXPRESS 11018
Optical lattices (Miranowicz et al., in progress)
NV-centres (Zagoskin et al., in progress)
Why are quantum metamaterials
interesting?
• Macroscopic quantum effects
• Testing limits of quantum mechanics
• Testing new theoretical methods
• Applications
Watching a Schrödinger’s cat jump
What if instead of scattering a
What if instead of scattering a quantum wave off a classical grating
quantum wave off a
we scatter a classical wave off a quantum grating?
classical grating we scatter a
wavecase:
offthean
In this work weclassical
considered the simplest
propagation of a
classical electromagnetic
through a 1D object?
array of charge qubits.
extendedwave
quantum
?
The simplest case: 1D quantum
metamaterial
Simplest case: Charge qubit line
• Rakhmanov, Zagoskin, Saveliev and Nori, Phys. Rev. B 77, 144507 (2008)
Flux qubit line
Zagoskin, Rakhmanov, Saveliev and Nori, Phys. Status Solidi B 246, No. 5 (2009) 955
Proof-of-principle test
a
f0 = 10.204 GHz
Ip = 195 nA
1 m
 (GHz)
b
13
1.0
0.8
0.6
0.4
0.2
0
12
I
tI
0
Is
c
Is
0
c
60
-80

t

-40
1.200
1.144
30
1.088
1.031
0
1
0.9750
arg(t) -30
0.9188
0.8625
-60
0
40
0.8063
0.8
80
0.7500
 (MHz)
0.6938
0.6375
11
t
0.6
0.5813
0.5250
0.4688
0.4125
0.4
0.3563
0.3000
10
-8
-6
-4
-2 0 2
-3
10 
4
6
8
Astafiev, Zagoskin et al., Science (2010)
Elastic scattering
a
0.4
-112 dBm
-132 dBm
Im (r)
0.2
0.0
-0.2
-122 dBm
-0.4
0.0
0.2
0.4 0.6
Re (r)
0.8
0.0
0.2
0.4 0.6
Re (r)
0.8
“Ambidextrous quantum
metamaterial”
The system can be in a superposition of left- and right-handed states
Initialization of a1D quantum metamaterial
Shvetsov, Satanin, Nori, Saveliev and Zagoskin (2013)
Initialization of a1D quantum metamaterial
Shvetsov, Satanin, Nori, Saveliev and Zagoskin (2013)
Pulse propagation through the 1D
metamaterial
2D and 3D phase-qubit quantum
metamaterials
Zagoskin, J. Opt. 14 (2012) 114011
Lasing in a 1D quantum metamaterial
Asai et al. (2014)
Asai et al. (2014)
Asai et al. (2014)
Josephson-like vortices
in a 1D quantum metamaterial
Asai et al. (2013)
Asai et al. (2014)
Asai et al. (2013)
Asai et al. (2014)
A model system:
Cayley tree (aka Bethe lattice)
Detecting a single photon’s wavefront
Zagoskin, Wilson, Everitt, Saveliev, Gulevich, Allen, Dubrovich and Il’ichev
(Scientific Reports, 2013)
Model Hamiltonian
Signal spectra for coherent (left) and Fock (right) input states
“Quantum imaging algorithms”
A. Sowa (2014)
Hardware implementation:
“Quantum perceptron”
Rigid quantum metamaterials
• (Saveliev and Zagoskin)
Rigid quantum metamaterials
• (Saveliev and Zagoskin)
Unusual unit elements: anapole QMM
• (Zagoskin, Shipulin, Il’ichev, Johansson and
Nori)
Next steps:
• A quantitative theory, which will direct
experimental effort in QMM and quantum
engineering and can only be developed in
a close collaboration between theory and
experiment
Further perspectives
• Using quantum engineering to test the limits of
quantum mechanics
• Realization of quantum metamaterial-based
systems for imaging, detection, quantum
communications and information processing (in
particular, for biomedical applications)
▫ Hypersensitive detectors
▫ Early stage diagnostics
• Developing quantum simulators of quantum
systems
• Developing and protecting intellectual property
• Developing spin-offs
Conclusions
• Research in quantum metamaterials has the potential
for both fundamental breakthroughs and developing
disruptive new technologies, new IP and business
opportunities
• The research bridges quantum information science,
condensed matter physics, physics of metamaterials,
quantum optics, and quantum physics, and is expected
to have significant impact on chemical, biological and
medical research and technologies
• Quantum metamaterials – a natural and most feasible
testing ground for the development of quantum
engineering