Marek Zukowski
It is shown here that Suarez [Found. Phys. 38, 583 (2008)] wrongly presents the assumptions behind the Leggett's inequalities, and their modified form used by Groeblacher et al. [Nature 446, 871 (2007)] for an experimental falsification of a certain class of non-local hidden variable models.
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This note is a reply to M. Navascués' claim that "all entangled states violate Leggett's crypto-nonlocality" [arXiv:1303.5124v2]. I argue that such a conclusion can only be reached if one introduces additional assumptions that further restrict Leggett's notion of "crypto-nonlocality". If a contrario one sticks only to Leggett's original axioms, there exist entangled states whose correlations are always compatible with Leggett's crypto-nonlocality---which is thus a genuinely different concept from quantum separability. I clarify in this note the relation between these two notions, together also…
Leggett-type nonlocal realist inequalities that have been derived to date are all contingent upon suitable geometrical constraints to be strictly satisfied by the spatial arrangement of the relevant measurement settings. This undesirable restriction is removed in the present work by deriving appropriate forms of nonlocal realist inequalities, one of which involve the least number of settings compared to all such inequalities derived earlier. The way such inequalities would provide a logically firmer basis for a clearer testing of Leggett-type nonlocal realist model vis-a-vis quantum mechanics …
It is shown that the before-before (or Suarez-Scarani) experiment refutes hidden variable models with a deterministic ("realistic") nonlocal part, and the experimental violation of Leggett-type inequalities models with a random nonlocal part and a biased random local one. Therefore the claim that Groeblacher et al. present "an experimental test of nonlocal realism" [Nature, 446, 871-875 (2007)] is misleading, and Marek Zukowski's comment [arXiv:0809.0072v1] misses the point. A new experiment is proposed.
Leggett-type inequalities for testing nonlocal realism in multipartite systems
该研究将Leggett型非定域实在模型推广到含偏振器设置的任意N体系统，推导得到普遍成立的基础双不等式，通过GHZ态演示了不等式的量子违背，证明多体系统的非定域实在论可实验检验。
Bell's inequality is established based on local realism. The violation of Bell's inequality by quantum mechanics implies either locality or realism or both are untenable. Leggett's inequality is derived based on nonlocal realism. The violation of Leggett's inequality implies that quantum mechanics is neither local realistic nor nonlocal realistic. The incompatibility of nonlocal realism and quantum mechanics has been urrently confirmed by photon experiments. In our work, we propose to test Leggett's inequality using the Aharonov-Casher effect. In our scheme, four entangled particles emitted fr…
Quantum theory predicts and experiments confirm that nature can produce correlations between distant events that are nonlocal in the sense of violating a Bell inequality. Nevertheless, Bell's strong sentence {\it Correlations cry out for explanations} remains relevant. The maturing of quantum information science and the discovery of the power of nonlocal correlations, e.g. for cryptographic key distribution beyond the standard Quantum Key Distribution schemes, strengthen Bell's wish and make it even more timely. In 2003, Leggett proposed an alternative model for nonlocal correlations [Found. P…
Trajectory-based Measure of Nonlocality in the Double Caldeira-Leggett Formalism
本文在Bohmian力学框架下，通过Bohmian速度对粒子位置的敏感性度量量子非定域性，研究了压缩态双粒子系统在闭合与开放（Caldeira-Leggett主方程）环境下的关联动力学，揭示了环境结构对纠缠退相干时间尺度的关键影响。
The Leggett inequality is a constraint on the bipartite correlation that admits certain types of non-localities. Existing tests mainly focused on the electromagnetic systems where measurement apparatus are assumed to be projective and sharp. However, in nature there are interactions that do not obey the same conservation laws for photon, and the actual measurements may subject to unavoidable uncertainties due to the fundamental physical principles. In this work, we generalize the Leggett inequality to incorporate the measurements that are unsharp and/or biased. It is found that the parity viol…
We analyze the class of nonlocal realistic theories that was originally considered by Leggett [Found. Phys. 33, 1469 (2003)] and tested by us in a recent experiment [Nature (London) 446, 871 (2007)]. We derive an incompatibility theorem that works for finite numbers of polarizer settings and that does not require the previously assumed rotational symmetry of the two-particle correlation functions. The experimentally measured case involves seven different measurement settings. Using polarization-entangled photon pairs, we exclude this broader class of nonlocal realistic models by experimentally…
Bell's theorem states that no local hidden variable model is compatible with quantum mechanics. Surprisingly, even if we release the locality constraint, certain nonlocal hidden variable models, such as the one proposed by Leggett, may still be at variance with the predictions of quantum physics. Here, we report an experimental test of Leggett's nonlocal model with solid-state spins in a diamond nitrogen-vacancy center. We entangle an electron spin with a surrounding weakly coupled $^{13}C$ nuclear spin and observe that the entangled states violate Leggett-type inequalities by more than four a…
It is argued that recent experiments refuting nonlocal realism, can also be considered as experiments refuting time-ordered nonlocality and, hence, confirming the result of the before-before experiment. However, the before-before experiment provides a broader refutation because it also falsifies the testable relativistic version of Bohm's nonlocal model. All this stresses the interest of a new before-before experiment demonstrating together the failure of time-ordered nonlocality and the violation of the Leggett's inequality.
Crypto-nonlocality in arbitrarily dimensional systems
本文将 Leggett 的 crypto-nonlocality 模型从二维推广到任意维度，并构造可实验检验的 Leggett 型不等式，以深化对量子关联的理解。
The Suarez-Scarani model is a non-covariant (frame-dependent) relativistic (time-ordered causal) nonlocal extension of quantum theory, which is not refuted by the experiments proposed in Reference [arXiv:1005.5173v1]. The covariant extensions considered in this Reference are actually self-contradictory and do not require experimental falsification.
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