Testing quantum physics in space using
high-mass matter-wave interferometry
Rainer Kaltenbaek*
*MAQRO Consortium
Quantum superposition
Which slit does each particle “really” go through?
A particle does not pass
either through one slit or
the other
The path of a particle is
not real.
From J. D. Norton, Universtiy of Pittsburgh
Does that hold true for massive objects?
Does Quantum Mechanics fail
for large/massive systems?
When do things
Become “real”?
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Beyond quantum theory?
• Inherent transition from quantum to classical
• Modification of Schrödinger equation
decoherence even for isolated systems
“collapse” models:
• F. Károlyházy, Nuovo Cimento A 52, 390 (1966)
• L. Diósi, PRA 105, 199 (1984)
• R. Penrose, e.g., Gen. Rel. Grav. 28, 581 (1996)
• Ghirardi, Rimini & Weber, PRD 34, 470 (1986)
• Continuous sponataneous localization (CSL), Ghirardi, Pearle & Rimini, PRA 42, 78 (1990)
• Ellis, Mohanty, Nanopoulos, Phys. Lett. B 221, 113 (1989)
Effects of quantum gravity
for high masses?
Gravitational decoherence:
• Metric fluctuations due to grav. wave background, A. Lambrecht, S. Reynaud & others
• Decoherence due to grav. redshift, I. Pikovski, C. Brukner & others
• Metric fluctuations due to quantum gravity (space-time foam), C. Lämmerzahl & others
Unfortunately beyond MAQRO
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Experimental tests?
Matter-wave interferometry
Current mass record – 104 amu
S. Eibenberger et al., PCCP 15 (35), 14696 (2013)
Quantum Optomechanics
Disadvantage: coupling to
environment via support.
G. D. Cole et al., Appl. Phys. Lett. 92, 261108 (2008)
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Optically trapped nanospheres
• optically trapped dielectric spheres
• combine optical-tweezer technology (A. Ashkin, PRL 24, 147 (1970)) with
optomechanics and atom-trapping toolbox
D. E. Chang et al., PNAS 107, 1005 (2010)
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O. Romero-Isart et al., New J. Phys. 12, 033015 (2010)
O. Romero-Isart et al., PRA 83, 013803 (2011)
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Matter-wave interference with nanospheres
Ground-based experiments
O. Romero-Isart , A. Pflanzer et al., PRL 107, 020405 (2011); O. Romero-Isart, PRA 84, 052121 (2011)
J. Bateman, S. Nimmrichter, K. Hornberger, H. Ulbricht,
Nature Comm. 5, 4788 (2014)
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Limitations for ground-based experiments
• free-fall times (~ 10s)
• statistics
• quality of micro-gravity (also vibrations)
limited to ≲ 108 amu
only limited tests of CSL model
For more general tests:
• higher mass
• longer free-fall times
• very good vacuum
• cryogenic temperatures
Case for Space – MAQRO
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Near-field vs. far-field interferometry
original MAQRO approach: near-field interferometry
alternative: Talbot (near-field) interference
Advantages:
• Established matter-wave interferometry technique
• High interference visibility possible
• “Reasonable” wavelengths (1064nm, 200nm)
Disadvantages:
• Classical “interference” fringes (shadowing)
• Narrow fringe spacing – hard requirements on thruster force
noise and/or accelerometers
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Classical vs QM visibility
Talbot (near-field) interference – based on work by J. Bateman et al.
J. Bateman, S. Nimmrichter, K. Hornberger, H. Ulbricht, Nature Comm. 5, 4788 (2014)
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Adapting this for MAQRO
Perform matter-wave interferometry – one particle at a time
cool
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expand
phase grating
Moriond, La Thuile, R. Kaltenbaek
wait, then measure
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Adapting this for MAQRO
Perform matter-wave interferometry – one particle at a time
cool
expand
phase grating
wait, then measure
~50s
24.03.2015
Moriond, La Thuile, R. Kaltenbaek
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Adapting this for MAQRO
Perform matter-wave interferometry – one particle at a time
cool
24.03.2015
expand
phase grating
Moriond, La Thuile, R. Kaltenbaek
wait, then measure
12
MAQRO – concept for Talbot approach
Perform matter-wave interferometry – one particle at a time
cool
expand
phase grating
wait, then measure
~50s
24.03.2015
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Adapting this for MAQRO
Perform matter-wave interferometry – one particle at a time
cool
expand
phase grating
wait, then measure
~50000 times(?)
Similar requirements as before but:
• need even better micro-gravity environment
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Predictions for MAQRO
QM vs. Classical interference visibility (109 amu)
Reduction of visibility due to decoherence
𝜌𝜌 𝑥𝑥, 𝑦𝑦 ≡ 𝑥𝑥 𝜌𝜌 𝑦𝑦
𝑑𝑑𝜌𝜌 𝑥𝑥, 𝑦𝑦
= −Λ 𝑥𝑥 − 𝑦𝑦
𝑑𝑑𝑡𝑡
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𝜌𝜌 𝑥𝑥, 𝑦𝑦
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Interference for very high masses
QM vs. Classical interference visibility (1010 amu)
QM vs. classical interference pattern
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MAQRO mission outline
•
•
•
•
MAQRO spacecraft & orbit based on LPF
Passive, radiative cooling & outgassing
Two subsystems outside & inside spacecraft
Nominal life time: 2 years
A. Pilan-Zanoni, J. Burkhardt, U. Johann, M. Aspelmeyer,
R. Kaltenbaek, G. Hechenblaikner, in preparation (2015)
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Conclusions & outlook
• submitted M3 & M4 proposal
• significant progress in mission design & technology
development
• successful initiation of MAQRO consortium
• national support from Austria, France, Germany,
Switzerland & the UK
Onward to M5:
• intensify collaborations
• further technology development
• proof-of-principle experiments
• support from more international partners
R. Kaltenbaek & the MAQRO consortium, Macroscopic
quantum resonators (MAQRO): 2015 Update,
arXiv: 1503.02640 (2015)
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Thanks
MAQRO Consortium
Coordinator: R. Kaltenbaek (Vienna)
Member groups: M. Arndt (Vienna), M. Aspelmeyer (Vienna), P. Barker (London), A. Bassi (Trieste), K. Bongs (Birmingham), S. Bose
(London), C. Braxmaier (Bremen), C. Brukner (Vienna), P.-F. Cohadon (Paris), A. M. Cruise (Birmingham), K. Dholakia (St. Andrews), W.
Ertmer (Hannover), A. Heidmann (Paris), U. Johann (Astrium), C. Lämmerzahl (Bremen), M. Kim (London), A. Lambrecht (Paris), G.
Milburn (Queensland), H. Müller (Berkley), L. Novotny (Zürich), M. Paternostro (Belfast), A. Peters (Berlin), E. Rasel (Hannover), S.
Reynaud (Paris), M. Rodriguez (Onera), A. Roura (Ulm), W. Schleich (Ulm), J. Schmiedmayer (Vienna), K. C. Schwab (Caltech), M. Tajmar
(Dresden), H. Ulbricht (Southhampton), R. Ursin (Vienna), V. Vedral (Oxford)
Austrian Research Promotion Agency
(MAQROsteps, Project no. 3589434)
MQES study (ESA contract Po P5401000400)
NanoTrapS project (ESA contract
4000105799/127NL/Cbi)
!THANK YOU!
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Appendix I: additional measurements
what if deviations already for 𝑚𝑚 < 108 ?
or Λ > 1013 m−2 s−1 ?
remember reduction of interference visibility:
alternative operational mode: observe expansion of wavepacket
𝑤𝑤 𝑡𝑡
2
2
= 𝑥𝑥� 𝑡𝑡
= 𝑤𝑤𝑠𝑠 𝑡𝑡
Λ > Λ min = 3 𝑚𝑚2
•
•
•
•
•
2
2 Λ ℏ2 3
+
𝑡𝑡
3 𝑚𝑚2
𝜎𝜎 𝑤𝑤𝑠𝑠 𝑡𝑡
𝑁𝑁 − 1 ℏ2 𝑡𝑡 3
black, solid: Λ min
blue, dashed: QG model, Ellis et al.
black, dashed: CSL model, original parameters
red, dot-dashed: Károlyházy model
green, dotted: Diósi-Penrose model
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Appendix II: Predictions of macrorealism
reduction of interference visibility
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VS
predicted decoherence parameters
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Appendix III: Heating of oscillator motion
similar to deviations in wave-packet expansion
(decoherence events heat oscillator motion)
needs to be investigated more closely for MAQRO
M. Bahrami, M. Paternostro, A. Bassi,
and H. Ulbricht, PRL 112, 210404 (2014)
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