三比特类GHZ态的Bell型不等式和非定域性

研究了一般形式类GHZ(Greenberger-Horne-Zeilinger)态的共生纠缠度及非定域性, 给出了类GHZ纠缠态的共生纠缠、Mermin不等式和Svetlichny不等式的解析表达式, 并通过数值计算讨论纠缠与非定域性之间的关系. 结果表明, 类GHZ纠缠态的共生纠缠和两个Bell型不等式描述的非定域性是一致的, Bell算符及其参量, 能够明显展示量子态的非定域特性. 关键词： 量子信息 类GHZ态 共生纠缠 Bell型不等式     

广义GHZ态的纠缠与非定域性

对GHZ态与W态叠加的三粒子广义GHZ态,用Svetlichny不等式,给出了其非定域性的解析表达式.用数值计算方法讨论了纠缠与非定域性之间的关系. 关键词： 广义GHZ态 剩余纠缠 Svetlichny不等式 非定域性     

基于法拉第旋转构造光子Bell态分析器和GHZ态分析器

基于偏振光被囚禁原子光腔反射后所获得的法拉第旋转构造了光子Bell态分析器和GHZ态分析器,并能实现非破坏地识别所有的光子Bell态和GHZ态.该方案不需要腔场的强耦合条件,在低品质光腔中也能实现,从而大大降低了实验难度.     

广义Greenberger-Horne-Zeilinger态纠缠度和Bell型不等式实验

利用制备的三光子偏振广义Greenberger-Horne-Zeilinger纠缠态,测量了三体纠缠度、Svetlichny不等式和广义Greenberger-Horne-Zeilinger态的密度矩阵.根据密度矩阵计算了三体纠缠度,测量得到了广义Greenberger-Horne-Zeilinger纠缠态的纠缠和非定域性之间的关系.结果表明:在实验误差范围内,三体纠缠度的实验测量值和理论值一致;Svetlichny算符的期望值和理论计算结果具有较好的一致性;体系非定域特性和体系的纠缠程度密切相关,当纠缠度减小时,非定域性减弱.     

用光子纠缠源验证Bell不等式

以Bell不等式的推广形式CHSH不等式为理论指导,利用自主搭建的双光子纠缠源制备光子纠缠态,通过测量不同条件下符合对比度计算Bell不等式,验证了量子力学的完备性.     

通过大失谐Jaynes-Cummings模型实现类自旋的腔场GHZ态

提出了一种利用大失谐的Jaynes-Cummings模型实现类自旋的腔场Greenberger-Horne-Zeilinger(缩写为GHZ)态的新方案,并通过对腔场宇称的测量,否定了局域隐变量理论,该方案不需要违背Bell不等式. 关键词：     

金刚石氮空位色心体系的量子纠缠态制备

利用金刚石氮空位色心体系耦合于一个双边的光子晶体腔(该光子晶体腔与两个波导耦合)来制备Bell态、GHZ态和团簇态。当光子被探测和进行幺正操作后,就得到纠缠态。同时计算了该体系的保真度,发现在近似参数条件下,该模型可得到较好结果。     

基于弱非线性实现非破坏性测量两光子Bell态及三光子Greenberger-Horne-Zeilinger态

基于弱非线性及线性光学元件提出非破坏性测量两光子Bell态及三光子 Greenberger-Horne-Zeilinger (GHZ)态方案. 方案中, 首先应用光束分束器及交叉克尔非线性介质对两光子Bell态进行对称性分析, 进而结合控制非门提出三光子分析方案实现对八个三光子GHZ态完全且非破坏性区分. 关键词： Bell态测量 Greenberger-Horne-Zeilinger态测量 弱非线性 量子非破坏性测量     

解说量子纠缠理论

量子纠缠态在量子信息处理,如量子隐形传态、量子密集码、量子纠错、量子保密通信、量子计算等过程中起了十分重要的作用.量子纠缠理论主要研究量子态的纠缠刻画、分类及其在量子信息处理中的应用.文章介绍了量子纠缠理论中的一些基本概念和结果,其中包括:量子力学的实在性、局域性的讨论与Bell不等式的联系,Bell不等式与量子态可分性间的关系;纯态和混合态可分性的定义及若干判别准则(包括矩阵正映照方法、部分转置判据、约化判据、重排判据、纠缠见证、协方差判据及局域测不准关系判据);部分纠缠度量的介绍(包括纠缠形成、并发度、相对熵、负度、缠结和纠缠帮助,以及纠缠度量的计算和上下界的估算).     

三量子比特Dicke模型中的两体和三体纠缠动力学

本文利用绝热近似方法和精确对角化方法研究三量子比特Dicke模型中的纠缠动力学.处于两种典型的纠缠态GHZ态和W态上的量子比特在时间演化过程中与辐射光场发生强耦合作用,在各种子系统间产生纠缠,通过分析这些纠缠的演化特性发现初始GHZ态的三体纠缠鲁棒性比W态强,这与旋波近似结论一致.与旋波近似下结果不同的是,两种态中任意一对量子比特间的纠缠都随时间演化到几乎为零,而三体纠缠随时间周期演化,且纠缠程度相对较强,说明系统中的强耦合作用通过抑制量子比特中的对纠缠来支持三体纠缠.     

Bell Theorem without Inequality for Some Generalized GHZ and W States

Bell＇s theorem without inequalities is applied for some general Greenberger-Horn-Zeilinger （GHZ） states and W states and a wide range of such states can exhibit all-versus-nothing conflict between local realism and quantum theory. The case of standard GHZ state is contained in our proposal. For some generalized GHZ states more intensive violation on local realism is manifested.     

Error correcting bell inequalities

Quantum error-correcting codes can protect multipartite quantum states from errors on some limited number of their subsystems (usually qubits). We construct a family of Bell inequalities which inherit this property from the underlying code and exhibit the violation of local realism, without any quantum information processing (except for the creation of an entangled state). This family shows no reduction in the size of the violation of local realism for arbitrary errors on a limited number of qubits. Our minimal construction requires preparing an 11-qubit entangled state.     

Loophole-free bell test for continuous variables via wave and particle correlations

We derive two classes of multimode Bell inequalities under local realistic assumptions, which are violated only by the entangled states negative under partial transposition in accordance with the Peres conjecture. Remarkably, the failure of local realism can be manifested by exploiting wave and particle correlations of readily accessible continuous-variable states, with very large violation of inequalities insensitive to detector efficiency, which makes a strong case for a loophole-free test.     

The Failure to Perform a Loophole-Free Test of Bell’s Inequality Supports Local Realism

It is argued that the long standing failure to show an uncontroversial, loophole-free, empirical violation of a Bell inequality should be interpreted as a support to local realism. After defining realism and locality, this as relativistic causality, the performed experimental tests of Bells inequalities are commented. It is pointed out that, without any essential modification of quantum mechanics, the theory might be compatible with local realism.     

Bell inequalities for continuous-variable correlations

We derive a new class of correlation Bell-type inequalities. The inequalities are valid for any number of outcomes of two observables per each of n parties, including continuous and unbounded observables. We show that there are no first-moment correlation Bell inequalities for that scenario, but such inequalities can be found if one considers at least second moments. The derivation stems from a simple variance inequality by setting local commutators to zero. We show that above a constant detector efficiency threshold, the continuous-variable Bell violation can survive even in the macroscopic limit of large n. This method can be used to derive other well-known Bell inequalities, shedding new light on the importance of non-commutativity for violations of local realism.     

“Solution” of the EPR Paradox: Negative, or Rather Fuzzy Probabilities?

Negative probabilities were several times proposed in the literature as a way to reconcile violation of Bell-type inequalities with the premise of local realism. It is argued that instead of using negative probabilities that have no physical meaning one can use for this purpose fuzzy probabilities that have sound and unambiguous interpretation.     

Do performed optical tests disprove local realism?

In all the earlier performed optical experiments on the Einstein, Podolsky, and Rosen paradox additional assumptions have been introduced and inequalities stronger than Bell's original one have been deduced. It is stressed that these experimental results violate these stronger inequalities but are compatible with Bell's original inequality. Therefore the experiments in question cannot provide a conclusive proof of the violation of local realism in nature but probably only show that the additional assumptions are not true.     

Experimental verification of a new Bell-type inequality

Arpan Das et al. proposed a set of new Bell inequalities (Das et al., 2017 [16]) for a three-qubit system and claimed that each inequality within this set is violated by all generalized Greenberger–Horne–Zeilinger (GGHZ) states. We investigate experimentally the new inequalities in the three-photon GGHZ class states. Since the inequalities are symmetric under the identical particles system, we chose one Bell-type inequality from the set arbitrarily. The experimental data well verified the theoretical prediction. Moreover, the experimental results show that the amount of violation of the new Bell inequality against locality realism increases monotonically following the increase of the tangle of the GGHZ state. The most profound physical essence revealed by the results is that the nonlocality of GGHZ state correlate with three tangles directly.