Photonic Bell violation closing the fair-sampling loophole Workshop “Quantum Information & Foundations of Quantum Mechanics” University of British Columbia, Vancouver, Canada 3 July 2013 Johannes Kofler Max Planck Institute of Quantum Optics (MPQ) Garching / Munich, Germany
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Photonic Bell violation closing the fair-sampling loophole Workshop “Quantum Information & Foundations of Quantum Mechanics” University of British Columbia,
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Photonic Bell violation
closing the fair-sampling loophole
Workshop “Quantum Information & Foundations of Quantum Mechanics”
University of British Columbia, Vancouver, Canada
3 July 2013
Johannes Kofler
Max Planck Institute of Quantum Optics (MPQ)Garching / Munich, Germany
Overview
• Assumptions in Bell’s theorem
- Realism
- Locality
- Freedom of choice
• Closing loopholes
- Locality
- Freedom of choice
- Fair sampling
• Conclusion and outlook
Quantum mechanics and hidden variables
Bohr and Einstein, 1925
1927 Kopenhagen interpretation(Bohr, Heisenberg)
1932 von Neumann’s (wrong) proof of non-possibility of hidden variables
1935 Einstein-Podolsky-Rosen paradox
1952 De Broglie-Bohm (nonlocal) hidden variable theory
1964 Bell‘s theorem on local hidden variables
1972 First successful Bell test (Freedman & Clauser)
Coincidence rate detected: 8 HzMeasurement time: 2400 s Number of total detected coinc.: 19200
Results
T. Scheidl, R. Ursin, J. K., T. Herbst, L. Ratschbacher, X. Ma, S. Ramelow, T. Jennewein, A. Zeilinger, PNAS 107, 10908 (2010)
Fair-sampling loophole
Unfair sampling: detection efficiency could be low and setting-dependent1
A = A(,), B = B(,)
• Simple local realistic model2:
1 P. M. Pearle, PRD 2, 1418 (1970)2 N. Gisin and B. Gisin, Phys. Lett. A 260, 323 (1999)3 I. Gerhardt, Q. Liu, A. Lamas-Linares, J. Skaar, V. Scarani, V. Makarov, C. Kurtsiefer, PRL 107, 170404 (2011)
• Efficiency is not optional in security-related tasks (device-independent quantum cryptography): faked Bell violations3
)sign(),(
aaA )sign(),(
bbB
||),(A
aabaBAbaE
S
BA2 2
d),(
1),(A
a
0),(A
a
1),(B
b
||),(B
bb
0),(B
b
:94
:94
:91
Reproduces the quantum predictions and has correct ratio of singles, coincidences and no clicks at all
- no post-selection or normalization- only one detector per side
1 A. Garg and N. D. Mermin, PRD 35, 3831 (1987)2 P. H. Eberhard, PRA 47, 747 (1993)3 J. F. Clauser and M. A. Horne, PRD 10, 526 (1974)
0)()(),(),(),(),( 1122122111 Bo
Aooooooooo SSCCCCJ
Source
local realism
Transition-edge sensors
1 Picture from: Topics in Applied Physics 99, 63-150 (2005)2 A. E. Lita, A. J. Miller, S. W. Nam, Opt. Express 16, 3032 (2008)
Working principle:
• Superconductor (200 nm thick tungsten film at 100 mK) at transition edge
• Steep dependence of resistivity on temperature
• Measurable temperature change by single absorbed photon
Superconducting transition-edge sensors1
Characteristics:
• High efficiency > 95 %1
• Low noise < 10 cps1
• Photon-number resolving
Setup
• Sagnac-type entangled pair source
• Non-max. entangled states
• Fiber-coupling efficiency >90%
• Filters: background-photon elimination >99%
VHrHVr
r
21
1
M. Giustina, A. Mech, S. Ramelow, B. Wittmann, J. K., J. Beyer, A. Lita, B. Calkins, T. Gerrits, S. W. Nam, R. Ursin, A. Zeilinger, Nature 497, 227 (2013)
Results
M. Giustina, A. Mech, S. Ramelow, B. Wittmann, J. K., J. Beyer, A. Lita, B. Calkins, T. Gerrits, S. W. Nam, R. Ursin, A. Zeilinger, Nature 497, 227 (2013)
0)()(),(),(),(),( 1122122111 Bo
Aooooooooo SSCCCCJ
Photon: only system for which all main loopholes are now closed(not yet simultaneously)
Jörn Beyer Adriana Lita Brice Calkins Thomas Gerrits
Sae Woo Nam Rupert Ursin
Sven Ramelow
Conclusion and outlook
• Loopholes important for quantum foundations & quantum cryptography
• Locality and freedom-of-choice loophole closed for photons
• Fair-sampling loophole (already closed for atoms and superconducting qubits) now closed for photons
• Photons: first system for which each of the three major loopholes has been closed, albeit in separate experiments
• For a loophole-free experiment:fast random number generators, precise timing, efficiency gains to compensate propagation losses due to increased distance