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http://www.nature.com/nature/journal/vaop/ncurrent/full/nature15759.html
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometres
B. Hensen,
H. Bernien,
A. E. Dréau,
A. Reiserer,
N. Kalb,
M. S. Blok,
J. Ruitenberg,
R. F. L. Vermeulen,
R. N. Schouten,
C. Abellán,
W. Amaya,
V. Pruneri,
M. W. Mitchell,
M. Markham,
D. J. Twitchen,
D. Elkouss,
S. Wehner,
T. H. Taminiau
& R. Hanson
Nature (2015) doi:10.1038/nature15759 Received 19 August 2015 Accepted 28 September 2015 Published online 21 October 2015
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature15759.html
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometres
B. Hensen,
H. Bernien,
A. E. Dréau,
A. Reiserer,
N. Kalb,
M. S. Blok,
J. Ruitenberg,
R. F. L. Vermeulen,
R. N. Schouten,
C. Abellán,
W. Amaya,
V. Pruneri,
M. W. Mitchell,
M. Markham,
D. J. Twitchen,
D. Elkouss,
S. Wehner,
T. H. Taminiau
& R. Hanson
Nature (2015) doi:10.1038/nature15759 Received 19 August 2015 Accepted 28 September 2015 Published online 21 October 2015
More than 50 years ago, John Bell proved that no theory of nature that obeys
locality and realism can reproduce all the predictions of quantum theory: in
any local-realist theory, the correlations between outcomes of measurements on
distant particles satisfy an inequality that can be violated if the particles
are entangled. Numerous Bell inequality tests have been reported however, all
experiments reported so far required additional assumptions to obtain a
contradiction with local realism, resulting in ‘loopholes’. Here we report a
Bell experiment that is free of any such additional assumption and thus directly
tests the principles underlying Bell’s inequality. We use an event-ready
scheme that enables the generation of robust entanglement between
distant electron spins (estimated state fidelity of 0.92 ± 0.03). Efficient spin
read-out avoids the fair-sampling assumption, while the use of fast random-basis
selection and spin read-out combined with a spatial separation of 1.3 kilometres
ensure the required locality conditions. We performed 245 trials that tested the
CHSH–Bell inequality20 S = 2 and found S = 2.42 ± 0.20 (where S quantifies the
correlation between measurement outcomes). A null-hypothesis test yields a
probability of at most P = 0.039 that a local- realist model for space-like
separated sites could produce data with a violation at least as large as we
observe, even when allowing for memory in the devices. Our data hence imply
statistically significant rejection of the local-realist null hypothesis. This
conclusion may be further consolidated in future experiments; for instance,
reaching a value of P = 0.001 would require approximately 700 trials for an
observed S = 2.4. With improvements, our experiment could be used for testing
less-conventional theories, and for implementing device-independent quantum-
secure communication and randomness certification.
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