Experimental Tests of Realistic Local Theories via Bell's Theorem

Aspect, Alain; Grangier, Philippe; Roger, G.

doi:10.1103/physrevlett.47.460

Cited by 1,930 publications

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“…Shocking as it may be, our world is not of this kind. Statistical inequalities, such as e = 1/4, derived on the assumption that the values of unmeasured physical quantities do exist and commonly referred to as Bell's inequalities 33 , have been violated in a number of painstaking experiments 33,34,35,36,37,38,39,40,41,42,43,44 . We shall not dwell on the philosophical implications of this experimental fact (volumes have been written on the subject), but simply point out that it should be embraced by all those who worry about secrecy because what does not exist cannot be eavesdropped, and so it is much easier to keep secrets in a non-classical world.…”

Section: Less Reality More Securitymentioning

confidence: 99%

The ultimate physical limits of privacy

Ekert

Renner

2014

Nature

128

104

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Among those who make a living from the science of secrecy, worry and paranoia are just signs of professionalism. Can we protect our secrets against those who wield superior technological powers? Can we trust those who provide us with tools for protection? Can we even trust ourselves, our own freedom of choice? Recent developments in quantum cryptography show that some of these questions can be addressed and discussed in precise and operational terms, suggesting that privacy is indeed possible under surprisingly weak assumptions.Edgar Allan Poe, an American writer and an amateur cryptographer, once wrote "… it may be roundly asserted that human ingenuity cannot concoct a cipher which human ingenuity cannot resolve …" 1 . Is it true? Are we doomed to be deprived of our privacy, no matter how hard we try to retain it? If the history of secret communication is of any guidance here, the answer is a resounding 'yes'. There is hardly a shortage of examples illustrating how the most brilliant efforts of code-makers were matched by the ingenuity of code-breakers 2 . Even today, the best that modern cryptography can offer are security reductions, telling us, for example, that breaking RSA, one of the most widely used public key cryptographic systems, is at least as hard as factoring large integers 3 . But is factoring really hard? Not with quantum technology. Indeed, RSA, and many other public key cryptosystems, will become insecure once a quantum computer is built 4 . Admittedly, that day is probably decades away, but can anyone prove, or give any reliable assurance, that it is? Confidence in the slowness of technological progress is all that the security of our best ciphers now rests on.This said, the requirements for perfectly secure communication are well understood. When technical buzzwords are stripped away, all we need to construct a perfect cipher is shared private randomness, more precisely, a sequence of random bits known as a 'cryptographic key'. Any two parties who share the key, we call them Alice and Bob (not their real names, of course), can then use it to communicate secretly, using a simple encryption method known as the one-time pad 5 . The key is turned into a meaningful message by one party telling the other, in public, which bits of the key should be flipped. An eavesdropper, Eve, who has monitored the public communication and knows the general method of encryption but not the key will not be able to infer anything useful about the message. It is vital though that the key bits be truly random, never reused, and securely delivered to Alice and Bob, who may be miles apart. This is not easy, but it can be done, and one can only be amazed how well quantum physics lends itself to the task of key distribution.Quantum key distribution, proposed independently by Bennett and Brassard 6 and by Ekert 7 , derives its security either from the Heisenberg uncertainty principle (certain pairs of physical properties are complementary in the sense that knowing one property necessarily precludes knowledge about the othe...

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Section: Less Reality More Securitymentioning

confidence: 99%

The ultimate physical limits of privacy

Ekert

Renner

2014

Nature

128

104

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“…Evidently, he did not recognize the correlation of observables A (s) 1 and B (s) 2 as an ordinary observable, to be measured by means of coincidence measurements like the EPR-Bell ones performed e.g. by Aspect et al [42,43]. Instead, he followed EPR in taking for granted existence of the correlation of the observables already if only one of the observables is measured.…”

Section: Epr and Correspondencementioning

confidence: 99%

Towards a Neo-Copenhagen Interpretation of Quantum Mechanics

Muynck

2004

Foundations of Physics

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The Copenhagen interpretation is critically considered. A number of ambiguities, inconsistencies and confusions are discussed. It is argued that it is possible to purge the interpretation so as to obtain a consistent and reasonable way to interpret the mathematical formalism of quantum mechanics, which is in agreement with the way this theory is dealt with in experimental practice. In particular, the essential role attributed by the Copenhagen interpretation to measurement is acknowledged. For this reason it is proposed to refer to it as a neo-Copenhagen interpretation.

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“…Thus, the maximal violation of Bell inequality in quantum mechanics has the extra √ 2 factor in the case of a pair of spins [16]. This violation was convincingly tested by Aspect et al [2,3] (see Figure 1) and the quantum entanglement was confirmed as a fundamental aspect of quantum mechanics. 1 To avoid confusion, the tensor product ⊗ is omitted below for simplicity.…”

Section: Bell Inequalitymentioning

confidence: 73%

“…In this case, we get the maximum value B 4 ∼ 1.45 (see Figure 3), then q ≥ (1.45) 2 2.1 and then log 2 2.1 1.07 > 1. Thus, we have shown that the violation of Bell inequalities increases exponentially with the number of modes to measure k. This indicates that some evidence that our universe has a quantum mechanical origin may survive in CMB data, even if quantum entanglement decays exponentially afterward due to decoherence.…”

Section: The Case Of a Non-bunch-davies Vacuummentioning

confidence: 78%

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Bell Inequality and Its Application to Cosmology

Kanno

Soda

2017

Galaxies

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Abstract:One of the cornerstones of inflationary cosmology is that primordial density fluctuations have a quantum mechanical origin. However, most physicists consider that such quantum mechanical effects disappear in CMB data due to decoherence. In this conference report, we show that the violation of Bell inequalities in an initial state of our universe increases exponentially with the number of modes to measure in inflation. This indicates that some evidence that our universe has a quantum mechanical origin may survive in CMB data, even if quantum entanglement decays exponentially afterward due to decoherence.

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Experimental Tests of Realistic Local Theories via Bell's Theorem

Abstract: We have measured the linear polarization correlation of the photons emitted in a radiative atomic cascade of calcium. A high-efficiency source provided an improved statistical accuracy and an ability to perform new tests. Our

Cited by 1,930 publications

References 18 publications

The ultimate physical limits of privacy

The ultimate physical limits of privacy

Towards a Neo-Copenhagen Interpretation of Quantum Mechanics

Bell Inequality and Its Application to Cosmology

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