We obtain the set of all detector configurations providing the maximal violation of the Bell inequality in the Clauser–Horne–Shimony–Holt form for a general (pure or mixed) state of two qubits. Next, we analyze optimal conditions for the Bell-inequality violations in the presence of local decoherence, which includes energy relaxation at the zero temperature and arbitrary pure dephasing. We reve...

By combining the postulates of macrorealism with Bell locality, we derive a qualitatively different hybrid inequality that avoids two loopholes that commonly appear in Leggett-Garg and Bell inequalities. First, locally invasive measurements can be used, which avoids the “clumsiness” Leggett-Garg inequality loophole. Second, a single experimental ensemble with fixed analyzer settings is sampled,...

Probabilities and correlations in EPR experiments. The EPR-Bohm-Aharonov [1] system of two correlated spin-half particles or qubits observed by spatially separated observers has often been used as an arena in which to probe fundamental questions about quantum theory. Typically there are four different configurations corresponding to four different experiments and one obtains no-go theorems on (...

Using the type-I SPDC process in BBO nonlinear crystal, we generate a polarization-entangled state near to maximally-entangled Bell-state with high-visibility (high-brightness) 98.50 ± 1.33% (87.71 4.45%) for HV (DA) basis. We calculate CHSH version of Bell inequality, as nonlocal realism test, and find strong violation from classical physics or any hidden variable theory, S = 2.71 0.10. Via me...

The $N$-qubit Greenberger-Horne-Zeilinger (GHZ) states are the maximally entangled of $N$ qubits, which have had many important applications in quantum information processing, such as key distribution and secret sharing. Thus how to distinguish GHZ from other becomes a significant problem. In this work, by presenting family generalized Clauser-Horne-Shimony-Holt (CHSH) inequality, we show that ...

In this article, we analyse the relationship between Bell violation and secure key rate of entanglement assisted quantum distribution (QKD) protocols. Specifically, address question whether is necessary or sufficient for communication. We construct a class states which do not show violation, however, can be used communication after local filtering. Similarly, identify another but generating eve...

We in this paper study quantum correlations for two neutral spin-particles coupled with a single-mode optical cavity through the usual magnetic interaction. Two-spin entangled states for both antiparallel and parallel spin-polarizations are generated under the photon coherent-state assumption. Based on the quantum master equation we derive the time-dependent quantum correlation of Clauser-Horne...

The standard Bell inequality experiments test for violation of local realism by repeatedly making local measurements on individual copies of an entangled quantum state. Here we investigate the possibility of increasing the violation of a Bell inequality by making collective measurements. We show that the nonlocality of bipartite pure entangled states, quantified by their maximal violation of th...

Maximally entangled states should maximally violate the Bell inequality. In this paper, it is proved that all two-qubit states that maximally violate the Bell-Clauser-Horne-Shimony-Holt inequality are exactly Bell states and the states obtained from them by local unitary transformations. The proof is obtained by using the certain algebraic properties that Pauli’s matrices satisfy. The argument ...