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Violation of local realism with freedom of choice

Violation of local realism with freedom of choice. Faculty of Physics, University of Vienna, Austria. Institute for Quantum Optics and Quantum Information Austrian Academy of Sciences. Johannes Kofler , Thomas Scheidl , Rupert Ursin , Sven Ramelow,

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Violation of local realism with freedom of choice

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  1. Violation of local realismwith freedom of choice Faculty of Physics, University of Vienna, Austria Institute for Quantum Optics and Quantum Information Austrian Academy of Sciences Johannes Kofler, Thomas Scheidl, Rupert Ursin, Sven Ramelow, Xiao-song Ma, Thomas Herbst, Lothar Ratschbacher, Alessandro Fedrizzi, Nathan Langford, Thomas Jennewein, and Anton Zeilinger APS March Meeting Dallas, March 23rd 2011

  2. Introduction Quantum mechanics and realism • 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 • Bell‘s theorem on local hidden variables • 1972 First successful Bell test (Freedman & Clauser) Bohr and Einstein, 1925

  3. Bell’s Assumptions λ Realism: [J. F. Clauser & A. Shimony, Rep. Prog. Phys. 41, 1881 (1978)] Hidden variables λdetermineoutcomeprobabilities: p(A,B|a,b,λ) [J. S. Bell, Physics 1, 195 (1964)] Locality: (OI) Outcome Independence: p(A|a,b,B,λ) = p(A|a,b,λ) & viceversa (SI) Setting Independence:p(A|a,b,λ) = p(A|a,λ) & viceversa Freedom of Choice: (FC) p(a,b|λ) =p(a,b)  p(λ|a,b) =p(λ) [J. S. Bell, Speakable and Unspeakable in Quantum Mechanics, p. 243 (2004)]

  4. Bell’s Theorem Realism + Locality + Freedom of Choice  Bell‘s Inequality CHSH form: |E(a1,b2) + E(a2,b1) + E(a2,b1) - E(a2,b2)|  2 The original Bell paper (1964) implicitly assumes freedom of choice: explicitly: A(a,b,B,λ) locality (outcome and setting independence) freedom of choice (λ|a,b) A(a,λ) B(b,λ) – (λ|a,c) A(a,λ) B(c,λ) implicitly:

  5. Loopholes Locality loophole: There may be a communication from the setting or outcome on one side to the outcome on the other side Closed by Aspect et al., PRL 49, 1804 (1982) & Weihs et al., PRL 81, 5039 (1998) Fair-sampling loophole: The measured events stem from an unrepresentative subensemble Closed by Rowe et al., Nature 409, 791 (2001) Freedom-of-choice loophole: The setting choices may be correlated with the hidden variables Closed by Scheidl et al., PNAS 107, 10908 (2010) [this talk]

  6. Space-Time Requirements Special relativity: no physical signal can travel faster than light space-like separated events cannot influence each other (OI) space-like separation of A and B (SI)  active setting choice + space-like separation of A (B) and b (a) t E A B a b x

  7. Space-Time Requirements Special relativity: no physical signal can travel faster than light space-like separated events cannot influence each other (OI) space-like separation of A and B (SI)  active setting choice + space-like separation of A (B) and b (a) (FC)  random setting choices + space-like separation ofa,b and E t l E l l A B l a b l l x

  8. Geography 144 km

  9. Space-Time Diagram B l l t a b A l 144 km l l l E l La Palma Tenerife l Locality: A is space-like separated from B (OI) and b (SI) B is space-like separated from A (OI) and a (SI) Freedom of choice: a and b are random and space-like separated from E x

  10. Geographic Details Tenerife 144 km free-space link La Palma NOT 144 km free-space link Source 6 km fiber channel Alice 144 km 1.2 km RF link OGS Bob QRNG QRNG

  11. Experimental Setup

  12. Experimental Results Coincidence rate detected: 8 Hz Measurement time: 2400 s  Number of total coinc. detected: 19200 Density matrix by state reconstruction: Fopt = 0.91 ± 0.01 T = 0.68 ± 0.04

  13. Important Remarks • In a fully deterministic world, neither the locality nor the freedom-of-choice loophole can be closed: • Setting choices would be predetermined and could not be space-like separated from the outcome at the other side (locality) or the particle pair emission (freedom-of-choice). • Thus, we need to assume stochastic local realism: • There, setting choices can be created randomly at specific points in space-time. • We have to consistently argue within local realism: • The QRNG is the best candidate for producing stochastic settings.

  14. Summary and Outlook • We violated Bell’s inequality closing two loopholes in one experiment: • First experiment to address and close (within reasonable assumptions) the freedom-of-choice loophole • Simultaneously closed the locality loophole • Now all three major loopholes – locality, fair-sampling, freedom-of-choice – have been closed individually • A loophole-free Bell test is still missing Einstein and Bohr, 1930

  15. Acknowledgments Thomas Scheidl Rupert Ursin Sven Ramelow Xiao-Song Ma Thomas Herbst Lothar Ratschbacher Alessandro Fedrizzi Nathan Langford Thomas Jennewein Anton Zeilinger

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