共查询到20条相似文献,搜索用时 31 毫秒
1.
ZHAO Ming-Jing LI Zong-Guo LI Bo FEI Shao-Ming WANG Zhi-Xi LI-JOST Xian-Qing 《理论物理通讯》2011,56(2):253-257
We investigate the nonlocality of Schmidt-correlated (SC) states, and present analytical expressions of the maximum violation value of Bell inequalities. It is shown that the violation of Clauser-Horne-Shimony-Holt (CHSH) inequality is necessary and sufficient for the nonlocality of two-qubit SC states, whereas the violation of the Svetlichny inequality is only a sufficient condition for the genuine nonlocality of three-qubit SC states. Furthermore, the relations among the maximum violation values, concurrence, and relative entropy entanglement are discussed. 相似文献
2.
《中国科学:物理学 力学 天文学(英文版)》2010,(11)
The effect of Dzialoshiski-Moriya (DM) interaction on the violation of Bell inequality for thermal states of interacting qubits via a two-qubit XXZ spin chain is investigated.Our results imply that the DM interaction and anisotropy taking a large positive value can enhance the Bell violation and improve the threshold temperatures of it.By the comparison between the Bell violation and thermal entanglement,we find that the threshold temperatures of thermal entanglement are higher than those of the Bell violation.This implies that some states are entangled but the Bell inequality is not violated. 相似文献
3.
In this paper we obtain violations of general bipartite Bell inequalities of order \({\frac{\sqrt{n}}{\log n}}\) with n inputs, n outputs and n-dimensional Hilbert spaces. Moreover, we construct explicitly, up to a random choice of signs, all the elements involved in such violations: the coefficients of the Bell inequalities, POVMs measurements and quantum states. Analyzing this construction we find that, even though entanglement is necessary to obtain violation of Bell inequalities, the entropy of entanglement of the underlying state is essentially irrelevant in obtaining large violation. We also indicate why the maximally entangled state is a rather poor candidate in producing large violations with arbitrary coefficients. However, we also show that for Bell inequalities with positive coefficients (in particular, games) the maximally entangled state achieves the largest violation up to a logarithmic factor. 相似文献
4.
We consider violation of CHSH inequality for states before and after entanglement swapping. We present a pair of initial states which do not violate CHSH inequality however the final state violates CHSH inequality for some results of Bell measurement performed in order to swap entanglement. 相似文献
5.
We investigate the entanglement dynamics and Bell violation of three-qubit quantum states under an environment consisting of an XY spin chain with Dzyaloshinski–Moriya (DM) interaction. From the results, we find that the entanglement dynamics depends not only on the DM interaction, the magnetic field, and the anisotropy parameter but also on the number of the freedom degrees of the environment. The decoherence-free subspaces of our model have been identified and the Bell violation of quantum states is also discussed. 相似文献
6.
通过求解系统的Milburn方程,研究了两个二能级原子和单模场相互作用系统中原子间纠缠和贝尔不等式破坏随时间的演化特性,讨论了偶极相互作用、场与原子的失谐量对纠缠度以及贝尔不等式破坏的影响.结果表明:原子间偶极-偶极相互作用对纠缠度和贝尔不等式破坏有显著影响,失谐量增大会使两原子的纠缠度和贝尔不等式破坏变大,并且两原子所能达到稳定的纠缠受偶极相互作用系数与失谐量两者之差的影响.同时还发现两原子的纠缠与贝尔不等式破坏并不是单调的函数关系,很小的纠缠也可以产生贝尔不等式破坏.
关键词:
Milburn理论
偶极-偶极相互作用
失谐量
贝尔不等式破坏 相似文献
7.
S.-B. Li J.-B. Xu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(2):377-383
We investigate the concurrence and Bell violation of the standard
Werner state or Werner-like states in the presence of collective
dephasing. It is shown that the standard Werner state and certain
kinds of Werner-like states are robust against the collective
dephasing, and some kinds of Werner-like states is fragile and
becomes completely disentangled in a finite-time. The threshold
time of complete disentanglement of the fragile Werner-like states
is given. The influence of external driving field on the
finite-time disentanglement of the standard Werner state or
Werner-like states is discussed. Furthermore, we present a simple
method to control the stationary state entanglement and Bell
violation of two qubits. Finally, we show that the theoretical
calculations of fidelity based on the initial Werner state
assumption well agree with previous experimental results. 相似文献
8.
One of the most significant and well-known properties of entangled states is that they may lead to violations of Bell inequalities and are thus inconsistent with any local-realistic theory. However, there are entangled states that cannot violate any Bell inequality, and in general the precise relationship between entanglement and observable nonlocality is not well understood. We demonstrate that a violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality can be demonstrated in a certain kind of Bell experiment for all entangled states. Our proof of the result consists of two main steps. We first provide a simple characterization of the set of states that do not violate the CHSH inequality even after general local operations and classical communication. Second, we prove that for each entangled state sigma, there exists another state rho not violating the CHSH inequality, such that rhomultiply sign in circlesigma violates the CHSH inequality. 相似文献
9.
10.
Dong Ding Ying-Qiu He Feng-Li Yan Ting Gao 《International Journal of Theoretical Physics》2016,55(10):4231-4237
By calculating entanglement measures and quantum violation of Bell-type inequality, we reveal the relationship between entanglement measure and the amount of quantum violation for a family of four-qubit entangled states. It has been demonstrated that the Bell-type inequality is completely violated by these four-qubit entangled states. The plot of entanglement measure as a function of the expectation value of Bell operator shows that entanglement measure first decreases and then increases smoothly with increasing quantum violation. 相似文献
11.
We experimentally demonstrate optimal entanglement distillation from two forms of two-qubit mixed states under local filtering operations according to the constructive method introduced by [F. Verstraete, Phys. Rev. A 64, 010101(R) (2001)10.1103/PhysRevA.64.010101]. In principle, our setup can be easily applied to distilling entanglement from arbitrary two-qubit partially mixed states. We also test the violation of the Clauser-Horne-Shinmony-Holt inequality for the distilled state from the first form of mixed state to show its "hidden nonlocality." 相似文献
12.
Bell inequality is violated by the quantum mechanical predictions made from an entangled state of the composite system. In this paper we examine this inequality and entanglement measures in the construction of the coherent states for two-qubit pure and mixed states. we find a link to some entanglement measures through some new parameters (amplitudes of coherent states). Conditions for maximal entanglement and separability are then established for both pure and mixed states. Finally, we analyze and compare the violation of Bell inequality for a class of mixed states with the degree of
entanglement by applying the formalism of Horodecki et al. 相似文献
13.
LIU Dan ZHAO Xin LONG Gui-Lu 《理论物理通讯》2008,49(2):329-332
Four-qubit entanglement has been investigated using a recent proposed entanglement measure, multiple entropy measures (MEMS). We have performed optimization for the nine different families of states of four-qubit system. Some extremal entangled states have been found. 相似文献
14.
Masanes L 《Physical review letters》2006,97(5):050503
A multipartite quantum state violates a Bell inequality asymptotically if, after jointly processing by general local operations an arbitrarily large number of copies of it, the result violates the inequality. In the bipartite case we show that asymptotic violation of the Clauser-Horne-Shimony-Holt inequality is equivalent to distillability. Hence, bound entangled states do not violate it. In the multipartite case we consider the complete set of full-correlation Bell inequalities with two dichotomic observables per site. We show that asymptotic violation of any of these inequalities by a multipartite state implies that pure-state entanglement can be distilled from it, although the corresponding distillation protocol may require that some of the parties join into several groups. We also obtain the extreme points of the set of distributions generated by measuring N quantum systems with two dichotomic observables per site. 相似文献
15.
F. Sciarrino G. Vallone G. Milani A. Avella J. Galinis R. Machulka A. M. Perego K. Y. Spasibko A. Allevi M. Bondani P. Mataloni 《The European physical journal. Special topics》2011,199(1):111-125
In the last years the attention of the scientific community on the generation of entangled states has constantly increased both for their importance in the foundation of quantum mechanics and for their application in the quantum computation and communication field. To these aims high quality of generated states is required. A standard procedure to produce entangled photons pairs is spontaneous down conversion process in nonlinear crystals. In this paper we report preparation of quantum entangled states using CW laser at 266 nm pumping the standard Kwiat’s source. We have been able to generate the full set of Bell’s states with very high purity, fidelity and Concurrence which have been estimated using standard tomography procedure. To proof the high degree of achieved entanglement, we performed a non-locality test obtaining a high violation of the CHSH inequality. 相似文献
16.
Thomas Krüger 《International Journal of Theoretical Physics》2009,48(4):1076-1089
Within the framework of a statistical interpretation of quantum mechanics entanglement (in a mathematical sense) manifests itself in the non-separability of the statistical operator ρ representing the ensemble in question. In experiments, on the other hand, entanglement can be detected, in the form of non-locality, by the violation of Bell’s inequality Δ≤2. How do these different viewpoints match? We employ a corrected von Neumann entropy to measure the (mathematical) degree of entanglement and show that, at least in the case of 2×2 dimensions, this function is directly related to Bell’s correlation function Δ. This relation can be well approximated by an ellipse equation which, for the first time, allows for a direct comparison of the two faces of entanglement. 相似文献
17.
Eric A. Carlen Elliott H. Lieb Robin Reuvers 《Communications in Mathematical Physics》2016,344(3):655-671
Unlike bosons, fermions always have a non-trivial entanglement. Intuitively, Slater determinantal states should be the least entangled states. To make this intuition precise we investigate entropy and entanglement of fermionic states and prove some extremal and near extremal properties of reduced density matrices of Slater determinantal states. 相似文献
18.
We investigate the nonlocal properties of graph states. To this aim, we derive a family of Bell inequalities which require three measurement settings for each party and are maximally violated by graph states. In turn, for each graph state there is an inequality maximally violated only by that state. We show that for certain types of graph states the violation of these inequalities increases exponentially with the number of qubits. We also discuss connections to other entanglement properties such as the positivity of the partial transpose or the geometric measure of entanglement. 相似文献
19.
Ikko Hamamura 《Physics letters. A》2018,382(36):2573-2577
Entanglement of quantum states is absolutely essential for modern quantum sciences and technologies. It is natural to extend the notion of entanglement to quantum observables dual to quantum states. For quantum states, various separability criteria have been proposed to determine whether a given state is entangled. In this Letter, we propose a separability criterion for specific quantum effects (binary observables) that can be regarded as a dual version of the Bell–Clauser–Horne–Shimony–Holt (Bell–CHSH) inequality for quantum states. The violation of the dual version of the Bell–CHSH inequality is confirmed by using IBM's cloud quantum computer. As a consequence, the violation of our inequality rules out the maximal tensor product state space, that satisfies information causality and local tomography. As an application, we show that an entangled observable which violates our inequality is useful for quantum teleportation. 相似文献
20.
Continuous Variable Entanglement and Violation of Bell Inequality for Two Modes in a Three-Level Cascade Atomic System
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Continuous variable entanglement and violation of Bell inequality for two modes are investigated in a three-level cascade atomic system. Entanglement of the system is demonstrated according to the entanglement criterion [Phys. Rev. Lett. 84 (2000)2722]. Violation of Bell inequality is studied within the framework of a quantum theory of multiwave mixing. It is shown that there are some states that are entangled but do not violate the Bell inequality. 相似文献