STE-QUEST M4
Peter Wolf
STE-QUEST M4 core team: K. Bongs(UK), P. Bouyer(F), C. Braxmaier (D),
D. Calonico (I), M. Cruise (UK), N. Gaaloul (D), L. Iess(I), P. Jetzer(CH),
W. von Klitzing (GR), S. Lecomte (CH), E. Rasel(D), M. Rothacher (CH)
S. Schiller(D), C. Sopuerta (E), G. Tino(I), P. Tuckey(F), P. Wolf(F), M. Zelan (S)
Motivation
• General Relativity is a classical theory, difficult to reconcile with
quantum field theory and the standard model of particle physics.
• Most unification models predict modifications of gravitational
phenomena at some small (generally unknown) level.
• Dark energy and dark matter may indicate deviations from our
known laws of gravitation.
• Many modified gravitational theories and corresponding
cosmological models contain long range scalar fields. Higgs boson
is the first known fundamental scalar field (short range).
• Low energy tests of fundamental gravitational physics can provide
pieces of the puzzle that are complementary to cosmological
observation or high energy physics in accelerators (LHC).
Scientific Context
Unified theories
string theory, quantum loop gravity ,...
?
?
GR
Theory of
gravitation
Local Lorentz Invariance
Universality of Clock Rates (LPI)
Universality of Free Fall (WEP)
Standard Model
Theory of
electromagnetic interaction
Theory of
weak
interaction
Theory of
strong interaction
Lorentz Invariance
CPT - Symmetry
exactly valid?
(courtesy S. Schiller)
STE-QUEST
Space-Time Explorer and Quantum Equivalence Space Test
• Elliptic orbit, 2500x33600 km, 63°
inclination
• 3.5 yrs mission lifetime
• 41K-87Rb double atom interferometer
• MWL for intercontinental ground clock
comparisons
•
•
•
Fundamental physics: Tests of all aspects of the EEP (Quantum WEP, LPI, LLI)
Geodesy: Unification of reference frames (SLR, VLBI, GNSS), Clock based geodesy
Time/Frequency metrology: Intercontinental clock comparisons at 10-18 level
Universality of Free Fall (WEP)
87Rb
41K
“STE-QUEST performs the experiment of the
motion of Rb and K in a quantum superposition”
L. Catani, "Galileo performs the experiment of the motion of weights from the Tower of Pisa in the presence
of the Grand Duke", Gallery of Modern Art of the Pitti Palace, Florence
•
•
•
•
Quantum test of UFF/WEP at 10-15, based on matter wave interference using BECs
Quantum superpositions: “Largest Atoms in the Universe”: 24 cm (102x larger than
individual wave packets)
De Broglie wavelength 1021x larger than for macroscopic test masses
Exploring the interface between Gravitation and Quantum Mechanics
WEP performance (1)
• ATI is shot noise dominated at 𝜎𝑎 = 1 × 10−11 𝑚𝑠 −2 𝜏 −1/2
• Assuming GRACE vibration levels, effect negligible  no drag-free required
• WEP test performance depends on local projection of g, and interferometer
contrast. A numerical simulation on baseline orbit shows that 2x10-15 performance
can be achieved after 1.2 y integration.
∆Φ2 =
∞
0
𝐻2 𝜔
2
𝑆𝑎 𝜔 𝑑𝜔
10 15
10 14
10 13
10 12
Measured GRACE vibration PSD [Flury2008],
and differential K-Rb sensitivity function for TK
= 5 s and two different values of TRb
10 11
0.01
0.10
1
10
100
rad
WEP performance (2)
• Systematic effects are related to gravity gradients, residual rotations, etc….
• For the effects to remain below 10-15 require 𝛿 𝑥0 < few nm, 𝛿 𝑣0 < few 10-10 m/s.
• Not surprising, for Microscope you also have eg. 𝛿 𝑥0 < few nm.
• Decouple and determine in data analysis. E.g. in Microscope the test masses are
only aligned mechanically to 𝛿 𝑥0 ≈10m but sufficient with <10-3 eccentricity.
• Turning STE-QUEST satellite by  (±10-3 rad) for two successive perigee passes
leads to a similar requirement of 𝛿 𝑥0 <10m.
There exists no principle that states: 𝛿 𝑥0 𝛿 𝑝0 ≤
ℏ
2
c.f. Ehrenfest!!
• Δ𝑥 and Δ𝑝 play no role (for max. quadratic L) [Storey & Cohen-Tannoudji, 1994]
• No “precise” measurement of 𝛿 𝑥0 is required
• More study required to derive final requirements on 𝛿 𝑥0 and 𝛿 𝑣0 (c.f. all the work
done on Microscope). Ongoing work!
Universality of Clock Rates (LPI)
Precise test of Sun gravitational time dilation:
• Ground-to-satellite links allow terrestrial clock
comparisons in common-view
• Test for anomalous coupling between source
(sun/moon) gravity and clock fields
• Measurement does not require operation of
atomic clock on satellite
 The time-independent signal allows a determination
of the geopotential difference UEarth(r1) – UEarth(r2)
To sun
(courtesy S. Schiller)
LPI performance
Visibility for Torino, Tokyo, Boulder
MC simulation result for 10 days
𝜈𝑇
1
= 1 − 2 𝛼𝐵 𝑈𝐵 − 𝛼 𝑇 𝑈𝑇 + Δ
𝜈𝐵
𝑐
• MC simulations show that you can reach Sun < 2.10-6 (Moon < 4.10-4) with less
than 1 year data.
•  contains corrections from sources assumed to behave normally (Earth, tidal
terms from external masses, etc…
• In GR Sun/Moon fields only appear in tidal terms 𝑂
have a EEP violation [PW & L. Blanchet, in preparation].
𝐺𝑀Δ𝑟 2
𝑟3𝑐2
, not so when you
Summary of Science objectives
Objective
STE-QUEST
Other
UCR/LPI Sun
2x10-6
10-2 (Krisher 1993)
10-4 (ACES 2016)
UCR/LPI Moon
4x10-4
10-2 (ACES 2016)
UFF/WEP
2x10-15
10-7 (Fray 2004, Schlippert 2014, Tarallo 2014)
7x10-9 (Peters 2001, Merlet 2010)
2x10-13 (Schlamminger 2008)
10-15 (-scope 2016)
Other science objectives:
•
Lorentz Invariance: Improvements by > factor 10 expected on several SME
parameters.
•
Geodesy: Unification of Reference Frames. Clock based geodesy at cm level.
•
T/F metrology: Distant clock comparisons at 10-18 level after a few days
integration: Essential for next generation ground clocks (at present 6x10-18
accuracy, 2x10-18 stability).