Loophole Free Bell Inequality Test

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Loophole Free Bell Inequality Test

#1  Postby Calilasseia » Dec 08, 2015 11:06 am

Recently, an experiment setting out to test Bell's Inequality, free from the loopholes that afflict previous experiments, was conducted in the Netherlands. The Nature paper is now a free download. Here it is:

Loophole-Free Bell Inequality Violation Using Electron Spins Separated By 1.3 Kilometres by 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, 528: 682-686 (21st October 2015) [Full paper downloadable from here]

Hensen et al, 2015 wrote:More than 50 years ago1, John Bell proved that no theory of nature that obeys locality and realism2 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 reported3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13; however, all experiments reported so far required additional assumptions to obtain a contradiction with local realism, resulting in ‘loopholes’13, 14, 15, 16. 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 scheme17, 18, 19 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 (detection loophole14, 15), 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 conditions13. 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 memory16, 21 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 communication22 and randomness certification23, 24.


Enjoy. :)
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Re: Loophole Free Bell Inequality Test

#2  Postby Darwinsbulldog » Dec 08, 2015 2:55 pm

Calilasseia wrote:Recently, an experiment setting out to test Bell's Inequality, free from the loopholes that afflict previous experiments, was conducted in the Netherlands. The Nature paper is now a free download. Here it is:

Loophole-Free Bell Inequality Violation Using Electron Spins Separated By 1.3 Kilometres by 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, 528: 682-686 (21st October 2015) [Full paper downloadable from here]

Hensen et al, 2015 wrote:More than 50 years ago1, John Bell proved that no theory of nature that obeys locality and realism2 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 reported3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13; however, all experiments reported so far required additional assumptions to obtain a contradiction with local realism, resulting in ‘loopholes’13, 14, 15, 16. 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 scheme17, 18, 19 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 (detection loophole14, 15), 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 conditions13. 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 memory16, 21 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 communication22 and randomness certification23, 24.


Enjoy. :)


I only either get a corrupted download or a pdf with the abstract, not the full paper. :ill:
My guess is that someone goofed, and then the problem was spotted and fixed to put it back behind the paywall again.
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Re: Loophole Free Bell Inequality Test

#3  Postby Calilasseia » Dec 08, 2015 11:27 pm

I've relinked to the ArxIv version. :)
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Re: Loophole Free Bell Inequality Test

#4  Postby Darwinsbulldog » Dec 09, 2015 12:50 am

Calilasseia wrote:I've relinked to the ArxIv version. :)

I didn't think the pre-print version would still be there after publication, so I didn't look! :doh:
Thanks young butterfly, u iz a gentleman and a scholar! :thumbup:
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Re: Loophole Free Bell Inequality Test

#5  Postby newolder » Dec 03, 2016 11:18 pm

Experimental setup now determined by light from distant stars:
https://arxiv.org/pdf/1611.06985v1.pdf
Bell’s theorem states that some predictions of quantum mechanics cannot be reproduced by a local-realist theory. That conflict is expressed by Bell’s inequality, which is usually derived under the assumption that there are no statistical correlations between the choices of measurement settings and anything else that can causally affect the measurement outcomes. In previous experiments, this “freedom of choice” was addressed by ensur- ing that selection of measurement settings via conventional “quantum random number generators” (QRNGs) was space-like separated from the entangled particle creation. This, however, left open the possibility that an unknown cause affected both the setting choices and measurement outcomes as recently as mere microseconds before each experimental trial. Here we report on a new experimental test of Bell’s inequality that, for the first time, uses distant astronomical sources as “cosmic setting generators.” In our tests with polarization-entangled photons, measurement settings were chosen using real-time observations of Milky Way stars while simultane- ously ensuring locality. We observe statistically significant 11.7σ and 13.8σ violations of Bell’s inequality with estimated p-values of 7.4 × 10−32 and 1.1 × 10−43, respectively, thereby pushing back by ∼600 years the most recent time by which any local-realist influences could have engineered the observed Bell violation.
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Re: Loophole Free Bell Inequality Test

#6  Postby crank » Dec 04, 2016 4:48 pm

I found this, I'm assuming it's discussing the same test, he's one of the authors.
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Re: Loophole Free Bell Inequality Test

#7  Postby newolder » Dec 04, 2016 6:15 pm

Handsteiner et al describe a third loophole that Hensen et al did not consider.

Even more recently, several cutting-edge experiments have demonstrated violations of Bell’s inequality while closing both the locality and fair-sampling loopholes simultaneously [17–21].

A third major loophole, known variously as the freedom-of-choice, measurement-independence, or setting-independence loophole [22–25], concerns the choice of measurement settings. In particular, the derivation of Bell’s inequality explicitly assumes that there is no statistical correlation between the choices of measurement settings and anything else that causally affects the measurement outcomes. Bell himself observed forty years ago that, “It has been assumed that the settings of instruments are in some sense free variables—say at the whim of experimenters—or in any case not determined in the overlap of the backward light cones” [22]. Recent theoretical work has demonstrated that models that relax this assumption, allowing for a modest correlation between the joint measurement settings and any causal influence on the measurement outcomes, can reproduce the quantum correlations [26–36].

Hensen et al is reference 17.

This third loophole is closed by using the observed colour of photons from remote stars to set the polarisation state for each measurement - as described in Handsteiner et al.
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Re: Loophole Free Bell Inequality Test

#8  Postby JoeB » Dec 05, 2016 10:04 am

I'm somewhat at a loss of the implications of these findings. What does the violation of Bell's inequality mean? I've been reading up on the subject, but it's incredibly complex to me...
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Re: Loophole Free Bell Inequality Test

#9  Postby newolder » Dec 05, 2016 3:43 pm

^ Simple but not incorrect. Hmmm, I'll have a go...

These experiments (and others) show how the world is quantum mechanical and does not behave classically - like in billiard ball collisions, for example. Usually, any quantum mechanical effects are smeared out across many objects and their interactions and are completely irrelevant at human, ‘middle world’ scales - see also, Bertlmann’s socks and the nature of reality.

In these experiments, however, the quantum mechanical nature of paired objects is maintained over large separations from each other and their mutual creation site through a process known as entanglement. Knowledge of one of the pair yields separate, though statistical, knowledge of the remote other. This would be useful in message encryption, say, since an eavesdropper between sender and recipient would only add noise to the channel and would probably destroy the channel completely.

Also, here's a connection to possible future quantum computing.
Many quantum technologies rely on quantum states that violate local realism, which means that they either violate locality (such as when entangled particles influence each other from far away) or realism (the assumption that quantum states have well-defined properties, independent of measurement), or possibly both. Violation of local realism is one of the many counterintuitive, yet experimentally supported, characteristics of the quantum world.

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Re: Loophole Free Bell Inequality Test

#10  Postby DavidMcC » Dec 16, 2016 3:43 pm

A free Bell test! Great, I'Il take two!
Oh, you mean a loophole-free Bell test? Why didn't you say so? :smug:
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Re: Loophole Free Bell Inequality Test

#11  Postby newolder » Jun 16, 2020 10:31 am

Regarding entanglement between pairs of quantum objects... When I learned about this stuff I was under the impression (wrong, as it turns out) that entanglement is a very "fragile" state of affairs and even setups being far from 0 Kelvin degrees, say a warm bath, would soon lose their entanglement coherence due to random encounters with photons. Recent results on an alkaline gas at 450 Kelvins, however, have falsified such notions.
Entanglement gets hot and messy
16 Jun 2020 Isabelle Dumé
...

The ICFO researchers, led by Morgan Mitchell, have now shown that the opposite strategy – actively promoting random interactions – can help generate and preserve entanglement too. In their experiment, they heated a collection of rubidinum-87 (87Rb) atoms to 450 K, creating a vapour of hot alkali atoms. They found that individual atoms in this vapour were not isolated but collided with each other every 20 microseconds. Each collision set their electrons spinning in random directions, producing a magnetization.

Mitchell and colleagues used a laser to monitor this magnetization via a series of measurements that enabled them to detect entanglement between the atoms and study the effect of the atomic collisions. The measurement technique is known as optical quantum non-demolition (QND) because it can measure the electron spins without disturbing them. “If a regular measurement is like a biopsy, in which material is taken and analysed, then a QND measurement can be thought of as like MRI, in which we obtain information without damaging the system,” Mitchell explains.

...

More @ PhysicsWorld source

Impacts for quantum biology, anyone?
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