两比特“X”态的量子非局域关联检验

基于Hardy定理,本文针对两比特"X"态这种混合态,进行了量子非局域关联检验研究。首先,简要阐述了针对任意量子态的Hardy定理检验逻辑,并给出了进行量子非局域关联的检验方法。进一步,本文以一种特定的"X"态为例(r=0.47),分析了保真度对"X"态量子非局域关联检验的影响,结果表明,只要该"X"态和量子纯态的保真度F≥0.885时,便能成功地检验量子非局域关联,且随着F的增加,成功检验的程度也将增加。最后,本文还给出了针对任意"X"态(即0相似文献   

Ontological Models,Preparation Contextuality and Nonlocality

The ontological model framework for an operational theory has generated much interest in recent years. The debate concerning reality of quantum states has been made more precise in this framework. With the introduction of generalized notion of contextuality in this framework, it has been shown that completely mixed state of a qubit is preparation contextual. Interestingly, this new idea of preparation contextuality has been used to demonstrate nonlocality of some \(\psi \) -epistemic models without any use of Bell’s inequality. In particular, nonlocality of a non maximally \(\psi \) -epistemic model has been demonstrated from preparation contextuality of a maximally mixed qubit and Schrödinger’s steerability of the maximally entangled state of two qubits (Leifer and Maroney, Phys Rev Lett 110:120401, 2013). In this paper, we, show that any mixed state is preparation contextual. We, then, show that nonlocality of any bipartite pure entangled state, with Schmidt rank two, follows from preparation contextuality and steerability provided we impose certain condition on the epistemicity of the underlying ontological model. More interestingly, if the pure entangled state is of Schmidt rank greater than two, its nonlocality follows without any further condition on the epistemicity. Thus our result establishes a stronger connection between nonlocality and preparation contextuality by revealing nonlocality of any bipartite pure entangled states without any use of Bell-type inequality.     

原子—场耦合系统中非局域性和纯度

本文讨论了光场初态和热库对原子——场耦合系统中量子非局域性和线性熵的影响。我们发现如果腔场无损耗且处于真空库，原子——场态会周期性的展现量子非局域性，原子和场的线性熵也会周期性地振荡，其周期和量子非局域性变化的周期相同。如果腔场损耗很弱而且热库的平均光子数很小，量子非局域性会消失，原子和场振荡的振幅逐渐减小。量子非局域性消失的速度取决于初始压缩相干态的幅度、腔的衰减系数和热库的平均光子数N。场越强、平均光子数和衰减系数越大，非局域性减弱的越快。     

Superactivation of Measurement-Induced Nonlocality

Nonlocality, as an essential, subtle and intriguing aspect of nature, has many different facets and manifestations. In quantum information theory, nonlocality is usually defined, characterized and quantified in the framework of entanglement and violation of certain Bell inequalities. An exciting phenomenon concerning entanglement-related nonlocality is the superactivation, symbolized as "0+0>0", which means that two systems, while do not possess nonlocality individually by themselves, may exhibit nonlocality when combined together in an independent fashion. In this work, we explore nonlocality from the measurement perspective and reveal the superactivation of measurement-induced nonlocality (MIN): When two bipartite states with vanishing MIN are combined together, the tensorizing state may possess non-zero MIN. Implications and applications are discussed.     

Quantum nonlocality of generic family of four-qubit entangled pure states

We directly introduce a Bell-type inequality for four-qubit systems. Using the inequality we investigate quantum nonlocality of a generic family of states |Gabcd[Phys. Rev. A 65 052112(2002)] and several canonical four-qubit entangled states. It has been demonstrated that the inequality is maximally violated by the so called "four-qubit the maximally entangled state |Gm" and it is also violated by four-qubit W state and a special family of states |Gab00. Moreover, a useful entanglement-nonlocality relationship for the family of states |Gab00is derived. Finally, we present a scheme of preparation of the state |Gmwith linear optics and cross-Kerr nonlinearities.     

Multipole surface solitons supported by the interface between linear media and nonlocal nonlinear media

We address multipole surface solitons occurring at the interface between a linear medium and a nonlocal nonlinear medium. We show the impact of nonlocality, the propagation constant, and the linear index difference of two media on the properties of the surface solitons. We find that there exist a threshold value of the degree of the nonlocality at the same linear index difference of two media, only when the degree of the nonlocality goes beyond the value, the multipole surface solitons can be stable.     

Multipartite quantum correlations among atoms in QED cavities

We study the nonlocality dynamics for two models of atoms in cavity quantum electrodynamics (QED); the first model contains atoms in a single cavity undergoing nearest-neighbor interactions with no initial correlation, and the second contains atoms confined in n different and noninteracting cavities, all of which were initially prepared in a maximally correlated state of n qubits corresponding to the atomic degrees of freedom. The nonlocality evolution of the states in the second model shows that the corresponding maximal violation of a multipartite Bell inequality exhibits revivals at precise times, defining, nonlocality sudden deaths and nonlocality sudden rebirths, in analogy with entanglement. These quantum correlations are provided analytically for the second model to make the study more thorough. Differences in the first model regarding whether the array of atoms inside the cavity is arranged in a periodic or open fashion are crucial to the generation or redistribution of quantum correlations. This contribution paves the way to using the nonlocality multipartite correlation measure for describing the collective complex behavior displayed by slightly interacting cavity QED arrays.     

纠缠薛定谔猫态的非局域性及其在热库中的演化

利用Bell-CHSH(Clauser-Horne-Shimony-Holt）不等式研究了两种纠缠的光学薛定猫态的量子非定域性及其在真空热库中的演化。计算表明，最大纠缠的薛定谔猫态具有最大非定域性。在真空热库中随着时间的演化，两种纠缠态的量子非定域性逐渐减弱直至消失。     

Monogamy of Measurement-Induced Nonlocality Based on Relative Entropy

In this paper, using relative entropy, we study monogamous properties of measurement-induced nonlocality based on relative entropy. Depending on different measurement sides, we provide necessary and sufficient conditions for two types of monogamy inequalities. By the concept of nonlocality monogamy score, we find a necessary condition of the vanished nonlocality monogamy score for arbitrary three-party states. In addition, two types of necessary and sufficient conditions of the vanished nonlocality monogamy scores are obtained for any pure states. As an application, we show that measurement-induced nonlocality based on relative entropy can be viewed as a "nonlocality witness" to distinguish generalized GHZ states from the generalized W states.     

Steady-state teleportation fidelity and Bell nonlocality in dissipative environments

We investigate quantum teleportation and Bell nonlocality for two channel qubits coupled via the Heisenberg interaction and subject to two independent dissipative environments. Compared with the case of two uncoupled qubits, it is shown that the interaction Hamiltonian is beneficial for enhancing the teleportation fidelity and Bell nonlocality, and remarkably, it can also be used to create nonclassical teleportation fidelity and Bell nonlocality even from the initial product states. Moreover, the interaction Hamiltonian guarantees the generation of steady-state nonclassical teleportation fidelity, which is independent of the initial state and therefore one can take any state as the initial channel state.     

Coherence-controlled entanglement and nonlocality of two qubits interacting with a thermal reservoir

We investigate the entanglement and the nonlocality of two qubits interacting with a thermal reservoir. It is shown that the time behavior of these quantities exhibits a strong dependence on the initial state of two qubits, and that the entanglement and the nonlocality of two qubits can be manipulated by changing the relative phases and the amplitudes of the polarized qubits.     

Uncertainty-induced quantum nonlocality

Based on the skew information, we present a quantity, uncertainty-induced quantum nonlocality (UIN) to measure the quantum correlation. It can be considered as the updated version of the original measurement-induced nonlocality (MIN) preserving the good computability but eliminating the non-contractivity problem. For 2×d$2\times d$-dimensional state, it is shown that UIN can be given by a closed form. In addition, we also investigate the maximal uncertainty-induced nonlocality.     

Bound nonlocality and activation

We investigate nonlocality distillation using measures of nonlocality based on the Elitzur-Popescu-Rohrlich decomposition. For a certain number of copies of a given nonlocal box, we define two quantities of interest: (i) the nonlocal cost and (ii) the distillable nonlocality. We find that there exist boxes whose distillable nonlocality is strictly smaller than their nonlocal cost. Thus nonlocality displays a form of irreversibility which we term "bound nonlocality." Finally, we show that nonlocal distillability can be activated.     

Dynamical nonlocality of the entangled coherent state in the phase damping model

This paper studies the dynamics of nonlocality for a bosonic entangled coherent state in a phase damping model. The density operator of the system is solved by using a superoperator method. The dynamics of nonlocality for the bosonic entangled coherent state is uncovered by the Bell operator based on the pseudospin operator of a light field. The dynamics of the nonlocality for this state has also been studied by other Bell operators. The result of the numerical calculations of the Bell function shows that the quantum nonlocality heavily depends on the chosen Bell operator.     

Thermodynamical approach to quantifying quantum correlations

We consider the amount of work which can be extracted from a heat bath using a bipartite state rho shared by two parties. In general it is less then the amount of work extractable when one party is in possession of the entire state. We derive bounds for this "work deficit" and calculate it explicitly for a number of different cases. In particuar, for pure states the work deficit is exactly equal to the distillable entanglement of the state. A form of complementarity exists between physical work which can be extracted and distillable entanglement. The work deficit is a good measure of the quantum correlations in a state and provides a new paradigm for understanding quantum nonlocality.     

等距离耦合腔系统中的非局域性

本文研究的物理系统由3个二能级原子和3个等距离单模腔构成. 3个单模腔分别处于等边三角形的3个顶点, 腔与腔之间通过光纤耦合. 采用Mermin-Ardehali-Belinksii-Klyshko不等式(简称MABK不等式)表征三体量子态的非局域性. 本文利用数值计算方法, 研究了原子初态或腔场初态为W态情况下三体系统量子态的MABK不等式违背, 讨论了腔模与光纤模间的耦合系数变化对MABK不等式违背的影响. 计算结果表明: 三原子量子态和三腔场量子态均呈现出MABK不等式违背, 并且随腔模与光纤模间耦合系数增大, 三原子量子态的非局域性增强.     

All-versus-nothing violation of local realism for two entangled photons

It is shown that the Greenberger-Horne-Zeilinger theorem can be generalized to the case with only two entangled particles. The reasoning makes use of two photons which are maximally entangled both in polarization and in spatial degrees of freedom. In contrast to Cabello's argument of "all versus nothing" nonlocality with four photons [Phys. Rev. Lett. 87, 010403 (2001)]], our proposal to test the theorem can be implemented with linear optics and thus is well within the reach of current experimental technology.     

Measurement-induced nonlocality and geometric quantum discord in two SC-charge qubits

By using geometric quantum discord and measurement-induced nonlocality, quantum correlations are investigated for two superconducting (SC) charge qubits that share a large Josephson junction where the field is assumed to be prepared initially in a coherent state. It is found that the difference between measure measurement-induced nonlocality and geometric quantum discord, of the final state of the two SC-charge qubits system which is especial case of X-states, is equal to a constant value. It is found that the quantum correlations and entanglement of the qubits are very sensitive to the mean number of the coherent photons. The entanglement exists in small intervals of death quantum discord and measurement-induced nonlocality. This is further evidence in support of the fact that quantum correlation and entanglement are not synonymous.     

Experimentally testing Hardy's theorem on nonlocality with entangled mixed states

Hardy's theorem on nonlocality has been verified by a series of experiments with two-qubit entangled pure states.However,in this paper we demonstrate the experimental test of the theorem by using the two-photon entangled mixed states.We first investigate the generic logic in Hardy's proof of nonlocality,which can be applied for arbitrary two-qubit mixed polarization entangled states and can be reduced naturally to the well-known logic tested successfully by the previous pure state experiments.Then,the optimized violations of locality for various experimental parameters are delivered by the numerical method.Finally,the logic argued above for testing Hardy's theorem on nonlocality is demonstrated experimentally by using the mixed entangled-photon pairs generated via pumping two type-I BBO crystals.Our experimental results shows that Hardy's proof of nonlocality can also be verified with two-qubit polarization entangled mixed states,with a violation of about 3.4 standard deviations.     

三模高斯态光场非局域性的增强

提出了增强三模高斯态光场非局域性的方案. 结果表明：通过一个IPS（inconlusive photon subtraction）过程的非高斯操作,可以将三模高斯态退变为非高斯态,利用Bell不等式检测发现对于较弱的输入高斯态非局域性能够得到加强. 关键词： 非局域性 三模高斯态