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arXiv:quant-ph/0007112

Generalization of the Peres criterion for local realism through nonextensive entropy

Constantino Tsallis, Seth Lloyd, Michel Baranger

Published Jul 28, 2000• 0 citations
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Abstract

A bipartite spin-1/2 system having the probabilities $\frac{1+3x}{4}$ of being in the Einstein-Podolsky-Rosen entangled state $|Ψ^-$$> \equiv \frac{1}{\sqrt 2}(|$$\uparrow>_A|$$\downarrow>_B$$-|$$\downarrow>_A|$$\uparrow>_B)$ and $\frac{3(1-x)}{4}$ of being orthogonal, is known to admit a local realistic description if and only if $x<1/3$ (Peres criterion). We consider here a more general case where the probabilities of being in the entangled states $|Φ^{\pm}$$> \equiv \frac{1}{\sqrt 2}(|$$\uparrow>_A|$$\uparrow>_B \pm |$$\downarrow>_A|$$\downarrow>_B)$ and $|Ψ^{\pm}$$> \equiv \frac{1}{\sqrt 2}(|$$\uparrow>_A|$$\downarrow>_B \pm |$$\downarrow>_A|$$\uparrow>_B)$ (Bell basis) are given respectively by $\frac{1-x}{4}$, $\frac{1-y}{4}$, $\frac{1-z}{4}$ and $\frac{1+x+y+z}{4}$. Following Abe and Rajagopal, we use the nonextensive entropic form $S_q \equiv \frac{1- Tr ρ^q}{q-1} (q \in \cal{R}; $$S_1$$= -$ $Tr$ $ ρ\ln ρ)$ which has enabled a current generalization of Boltzmann-Gibbs statistical mechanics, and determine the entire region in the $(x,y,z)$ space where local realism is admissible. For instance, in the vicinity of the EPR state, classical realism is possible if and only if $x+y+z<1$, which recovers Peres' criterion when $x=y=z$. In the vicinity of the other three states of the Bell basis, the situation is identical. A critical-phenomenon-like scenario emerges. These results illustrate the computational power of this new nonextensive-quantum-information procedure.

DOI
10.48550/arxiv.quant-ph/0007112

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A bipartite spin-1/2 system having the probabilities (1+3x)/4(1+3x)/4(1+3x)/4 of being in the Einstein-Podolsky-Rosen (EPR) entangled state $|{\ensuremath{\Psi}}^{\ensuremath{-}}〉\ensuremath{\equiv}(1/\sqrt{2})(|\ensuremath{\uparrow}{〉}_{A}|\ensuremath{\downarrow}{〉}_{B}\ensuremath{-}|\ensuremath{\downarrow}{〉}_{A}|\ensuremath{\uparrow}{〉}_{B})$ and $3(1\ensuremath{-}x)/4$ of being orthogonal is known to admit a local realistic description if and only if x<1/3x<1/3x<1/3 (Peres criterion). We consider here a more general case where the probabilities of being in the entangled states $|{\ensuremath{\Phi}}^{\ifmmode\pm\else\textpm\fi{}}〉\ensuremath{\equiv}(1/\sqrt{2})(|\ensuremath{\uparrow}{〉}_{A}|\ensuremath{\uparrow}{〉}_{B}\ifmmode\pm\else\textpm\fi{}|\ensuremath{\downarrow}{〉}_{A}|\ensuremath{\downarrow}{〉}_{B})$ and $|{\ensuremath{\Psi}}^{\ifmmode\pm\else\textpm\fi{}}〉\ensuremath{\equiv}(1/\sqrt{2})(|\ensuremath{\uparrow}{〉}_{A}|\ensuremath{\downarrow}{〉}_{B}\ifmmode\pm\else\textpm\fi{}|\ensuremath{\downarrow}{〉}_{A}|\ensuremath{\uparrow}{〉}_{B})$ (Bell basis) are given, respectively, by $(1\ensuremath{-}x)/4,$ $(1\ensuremath{-}y)/4,$ $(1\ensuremath{-}z)/4,$ and (1+x+y+z)/4.(1+x+y+z)/4.(1+x+y+z)/4. Following Abe and Rajagopal, we use the nonextensive entropic form ${S}_{q}\ensuremath{\equiv}(1\ensuremath{-}\mathrm{Tr}{\ensuremath{\rho}}^{q})/(q\ensuremath{-}1)$$(q\ensuremath{\in}\mathcal{R}{;S}_{1}=\ensuremath{-}\mathrm{Tr}\ensuremath{\rho}\mathrm{ln}\ensuremath{\rho})$ which has enabled a current generalization of Boltzmann-Gibbs statistical mechanics, and determine the entire region in the (x,y,z)(x,y,z)(x,y,z) space where the system is separable. For instance, in the vicinity of the EPR state, separability occurs if and only if x+y+z<1,x+y+z<1,x+y+z<1, which recovers Peres' criterion when x=y=z.x=y=z.x=y=z. In the vicinity of the other three states of the Bell basis, the situation is identical. These results illustrate the computational power of this nonextensive-quantum-information procedure. In addition to this, a critical-phenomenon-like scenario emerges which enrichens the discussion.
Local realism has been knocked down by the experiments with entangled pairs of particles based on Bell's theorem(J. S. Bell, Physics (Long Island City, N.Y.) 1, 195 (1964)). However, there has been continuing debate on whether locality or realism is the problem. In this work, we analyzed the Einstein-Podolsky-Rosen thought experiment of Bohm's version using information theory and thermodynamics. The inference of non-locality from EPR experiments will be against the principle of non-realism of quantum mechanics. Therefore, the experiments about quantum entanglement cannot provide any proof to accuse locality.
The Einstein-Podolsky-Rosen (EPR) paradox gives an argument for the incompleteness of quantum mechanics based on a plausible criterion for reality, as well as the assumption of locality. A general view is that the argument is compromised, because EPR's premises are falsified by Greenberger-Horne-Zeilinger (GHZ) and Bell experiments. In this paper, we present an EPR argument based on premises not falsified by these experiments. First, we consider macroscopic EPR-Bohm, Bell, and GHZ experiments using spins ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{S}}_{\ensuremath{\theta}}$ defined by two macroscopically distinct states. The analyzers that realize the unitary operations ${U}_{\ensuremath{\theta}}$ determining the measurement settings $\ensuremath{\theta}$ are nonlinear devices creating macroscopic superposition states. We note two definitions of macroscopic realism (MR). For a system with two macroscopically distinct states available to it, MR posits a predetermined outcome for the measurement ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{S}}_{\ensuremath{\theta}}$ distinguishing between the states. Deterministic macroscopic realism assumes MR for the system defined prior to the interaction ${U}_{\ensuremath{\theta}}$ being carried out but is falsifiable by the macroscopic Bell and GHZ proposals. Motivated by arguments to uphold MR (without resorting to decoherence), as well as no-signaling and the properties of a meter, we define a set of premises referred to as weak macroscopic realism (wMR). Weak macroscopic realism (wMR) posits MR for the system after ${U}_{\ensuremath{\theta}}$, at the time tf{t}_{f}tf​---when the system is prepared with respect to the measurement basis, ready for a ``pointer'' measurement and readout. For this system, wMR posits that the outcome of ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{S}}_{\ensuremath{\theta}}$ is determined and not changed by interactions that might subsequently occur at a remote system BBB. The premise wMR also posits a weaker version of EPR's criterion for reality. Importantly, we show that the GHZ and Bell predictions are consistent with wMR. Yet, an EPR paradox arises for a macroscopic EPR-Bohm state, based on wMR. As considered by Schr\"odinger, it is possible to measure two complementary spins of system AAA simultaneously, ``one by direct, the other by indirect measurement'': If we assume wMR, then once both settings are fixed, the outcomes of the two spins are both determined. We revisit the original EPR paradox and find a similar result: An EPR argument can be based on a set of premises, weak local realism, which we show are not falsifiable by GHZ or Bell experiments.
We show using a numerical approach, which gives necessary and sufficient conditions for the existence of local realism, that the bound entangled state presented in Bennett et al. [Phys. Rev. Lett. 82, 5385 (1999)] admits a local and realistic description. We also find the lowest possible amount of some appropriate entangled state that must be ad-mixed to the bound entangled state so that the resulting density operator has no local and realistic description and as such can be useful in quantum communication and quantum computation.
In a previous paper tests for entanglement for two-mode systems involving identical massive bosons were obtained. In the present paper we consider sufficiency tests for Einstein-Podolsky-Rosen (EPR) steering in such systems. We find that spin squeezing in any spin component, a Bloch vector test, the Hillery-Zubairy planar spin variance test, and squeezing in two-mode quadratures all show that the quantum state is EPR steerable. We also find a generalization of the Hillery-Zubairy planar spin variance test for EPR steering. The relation to previous correlation tests is discussed. This paper is based on a detailed classification of quantum states for bipartite systems. States for bipartite composite systems are categorized in quantum theory as either separable or entangled, but the states can also be divided differently into Bell local or Bell nonlocal states in terms of local hidden variable theory (LHVT). For the Bell local states there are three cases depending on whether both, one of or neither of the LHVT probabilities for each subsystem are also given by a quantum probability involving subsystem density operators. Cases where one or both are given by a quantum probability are known as local hidden states (LHSs) and such states are nonsteerable. The steerable states are the Bell local states where there is no LHS, or the Bell nonlocal states. The relationship between the quantum and hidden variable theory classification of states is discussed.
Based on a recently proposed model of physical reality and an underlying criterion of nonlocality for contexts [A. L. O. Bilobran and R. M. Angelo, Europhys. Lett. 112, 40005 (2015)], we introduce a quantifier of realism-based nonlocality for bipartite quantum states, a concept that is profoundly different from Bell nonlocality. We prove that this measure reduces to entanglement for pure states, thus being free of anomalies in arbitrary dimensions, and identify the class of states with null realism-based nonlocality. Then we show that such a notion of nonlocality can be positioned in a low level within the hierarchy of quantumness quantifiers, meaning that it can occur even for separable states. These results open a different perspective for nonlocality studies.