两纠缠原子与相干态光场相互作用过程中光场的量子特性

采用时间演化算符和数值计算方法,研究了两全同二能级纠缠原子与相干态光场相互作用过程中光场的量子特性,结果表明:两原子初始纠缠度和相干态光场强度对系统光场的二阶相干性质和压缩效应有很大的影响.     

用两粒子纠缠对进行{\bf\large{N}}粒子纠缠态的隐形传送

本文提出了一个方案:将三粒子纠缠态从一个发送者传给两个接收者之一,并将其推广到N粒子纠缠态的传送。这里，我们仅用两粒子纠缠对作通道就实现了N粒子纠缠态的传送。此方案相比以往的方案节省了大量纠缠资源，且成功传送的几率达到了1。     

两纠缠原子与光场相互作用系统场熵演化特性

研究了两纠缠原子与相干态光场相互作用系统场熵的时间演化特性,运用全量子力学理论和数值方法,讨论了初始两原子所处的纠缠状态、纠缠度和腔内光场的强弱对场熵的影响.随着光场平均光子数的增加,系统场熵均值和振荡频率增大;光场较弱时,场熵呈现一定的周期性振荡;光场增强后,场熵呈现出周期性的崩塌与回复,且随初始两原子纠缠度的增加,场熵的振幅增大.     

两纠缠原子与相干态光场相互作用的动力学

采用时间演化算符和数值计算方法,研究了两全同二能级纠缠原子与相干态光场相互作用的动力学,结果表明:原子布居和偶极压缩特性与两原子体系纠缠度和相干态光场强度相关联.     

Dissipative preparation of a steady three-dimensional entangled state via quantum-jump-based feedback

A robust and scalable scheme to generate a steady three-dimensional entangled state for a V-type atom and a A- type atom trapped in a strongly dissipative bimodal cavity is proposed by direct feedback control based on quantum-jump detection. The robustness of this scheme reflects in the insensitivity to detection inefficiencies and the strong ability against the parameter fluctuations in the feedback, driving, and coupling strengths. The influence of atomic spontaneous emission can be suppressed by using the local feedback control. The scalability is ensured that N-dimensional entangled states of two atoms can be deterministically generated.     

Quantum anonymous voting systems based on entangled state

Based on quantum entanglement, secure anonymous ballot systems are introduced to realize voting among numerous candidates in this paper. By searching individuals, each voter may cast a vote for his desired candidates of which number may be more than one. Therefore, the system based on the proposed algorithm may be applied voting among many candidates, such as a network ballot with the development of a quantum network. Finally, the security of the present scheme is investigated.     

Squeezing entangled state of two particles with unequal masses

For two unequal-mass particles, we construct the entangled state representation and then derive the corresponding squeezing operator. This squeezing operator has a natural realization in the entangled state representation, which exhibits the intrinsic relation between squeezing and quantum entanglement. This squeezing operator involves both two-mode squeezing and the direct product of two single-mode squeezings. The maximum squeezing occurs when the two particles possess equal mass. When two particles' mass difference becomes large, the component of the two single-mode squeezings becomes dominant.     

两纠缠原子与光场相互作用系统原子的纠缠特性

研究了两纠缠原子与单模相干态光场相互作用系统中原子纠缠度的时间演化特性,运用全量子理论和数值计算的方法,应用Concurrence纠缠度量标准,讨论了原子初始时刻的纠缠状态和光场强度对两原子纠缠度的影响.结果表明:双原子系统初始纠缠度越大,两原子间的纠缠在演化过程中的峰值也越大;随着光场强度的增加,两原子纠缠度的振荡曲线逐渐表现出崩塌一回复现象,周期性也越来越明显.     

两纠缠原子与光场相互作用系统原子的纠缠特性

研究了两纠缠原子与单模相干态光场相互作用系统中原子纠缠度的时间演化特性,运用全量子理论和数值计算的方法,应用Concurrence纠缠度量标准,讨论了原子初始时刻的纠缠状态和光场强度对两原子纠缠度的影响.结果表明：双原子系统初始纠缠度越大,两原子间的纠缠在演化过程中的峰值也越大;随着光场强度的增加,两原子纠缠度的振荡曲线逐渐表现出崩塌-回复现象,周期性也越来越明显.     

Projection of two biphoton qutrits onto a maximally entangled state

Bell state measurements, in which two quantum bits are projected onto a maximally entangled state, are an essential component of quantum information science. We propose and experimentally demonstrate the projection of two quantum systems with three states (qutrits) onto a generalized maximally entangled state. Each qutrit is represented by the polarization of a pair of indistinguishable photons-a biphoton. The projection is a joint measurement on both biphotons using standard linear optics elements. This demonstration enables the realization of quantum information protocols with qutrits, such as teleportation and entanglement swapping.     

The squeezing entangled state of two particles with unequal mass

For two unequal-mass particles,we construct the entangled state representation and then derive the corresponding squeezing operator.This squeezing operator has a natural realization in the entangled state representation,which exhibits the intrinsic relation between squeezing and quantum entanglement.This squeezing operator involves both two-mode squeezing and the direct product of two single-mode squeezings.The maximum squeezing occurs when the two particles possess equal mass.When the two particles’ mass difference becomes large,the component of the two single-mode squeezings becomes dominant.     

基于投影纠缠对态算法优化的研究

二维强关联电子量子格点系统的投影纠缠对态(PEPS)算法是数值计算领域中研究二维强关联电子量子格点系统最为重要的张量网络算法.基于PEPS算法研究二维量子XYX模型与二维量子Ising模型,本文对PEPS算法进行了一些优化和改进研究,这些优化和改进主要体现在如何进行PEPS张量的更新与如何进行物理观测量的计算这两个方面,从而可以大大提高计算资源的利用.因而优化和改进后的PEPS算法可为研究热力学极限下的二维强关联电子量子格点系统的量子相变和量子临界现象提供一种更有效的强大的工具.     

利用两个纠缠对隐形传送三原子W态

提出利用两个Einstein-Podolsky-Rosen(EPR)态作为量子信道隐形传送任意三原子W态的方案,并将该方案推广至隐形传送任意N（N 4）原子W态. 研究了实施方案的两种方法,给出了完成隐形传态的一种新思路：解纠缠—隐形传送—重构纠缠.讨论了量子信道受噪声影响时隐形传态的保真度. 结果表明,当作为量子信道的两个最大纠缠态受到噪声影响时,隐形传态的保真度不仅与量子信道的纠缠度有关,还与待传送态中某一子系统的共生纠缠度有关. 所提出的方案具有操作简便,节省量子信道纠缠资源的特点.     

Mode coupling theory of hydrodynamics and steady state systems

We construct a formal mode coupling theory for hydrodynamic systems which includes contributions from all powers of the hydrodynamic variables. This theory is applied to nonequilibrium steady state systems. A generalization of the local equilibrium distribution is used to describe the nonequilibrium state. This distribution independently constrains all moments of the hydrodynamic variables. The infinite hierarchy of equations for the moments of the hydrodynamic variables is truncated using an inverse system size expansion. Explicit results are obtained for the time correlation functions of fluids with a linear temperature gradient or a linear shear. These results agree with previous studies of these steady states.     

Creation of entangled state between two spaced NV centers in diamond

A method for creating an entangled state between two NV centers in a diamond that do not interact directly with each other is studied. The method is based on the excitation of centers via a half divider (a 50% beamsplitter) with the subsequent coherent inversion of the spin of the excited center and the detection of a photon emitted by the excited center. The parameters of a multimode single-photon pulse that make it possible to achieve a maximally possible excitation of the centers at a given solid angle of the focusing of the light on the center are found. The probability to create an entangled state in relation to the parameters of the initial state of a photon, the turn-on and turn-off times of the microwave pulse and the light focusing solid angle is determined. Optimal values of these parameters that ensure a maximal probability of the entanglement creation are determined.     

利用两个纠缠对隐形传送任意三原子W态

提出利用两个Einstein-Podolsky-Rosen(EPR)态作为量子信道隐形传送任意三原子W态的方案,并将该方案推广至隐形传送任意N(N≥4)原子W态.研究了实施方案的两种方法,给出了完成隐形传态的一种新思路:解纠缠-隐形传送-重构纠缠.讨论了量子信道受噪声影响时隐形传态的保真度.结果表明,当作为量子信道的两个最大纠缠态受到噪声影响时,隐形传态的保真度不仅与量子信道的纠缠度有关,还与待传送态中某一子系统的共生纠缠度有关.所提出的方案具有操作简便,节省量子信道纠缠资源的特点.     

Two-qubit entangled state teleportation via optimal POVM and partially entangled GHZ state

Quantum teleportation is of significant meaning in quantum information. In this paper, we study the probabilistic teleportation of a two-qubit entangled state via a partially entangled Greenberger- Horne-Zeilinger (GHZ) state when the quantum channel information is only available to the sender. We formulate it as an unambiguous state discrimination problem and derive exact optimal positive-operator valued measure (POVM) operators for maximizing the probability of unambiguous discrimination. Only one three-qubit POVM for the sender, one two-qubit unitary operation for the receiver, and two cbits for outcome notification are required in this scheme. The unitary operation is given in the form of a concise formula, and the fidelity is calculated. The scheme is further extended to more general case for transmitting a two-qubit entangled state prepared in arbitrary form. We show this scheme is flexible and applicable in the hop-by-hop teleportation situation.     

用一个纠缠态实现多粒子纠缠态的量子隐形传送

提出分别在二维和高维系统中利用一个纠缠态作量子通道实现M粒子纠缠态的量子隐形传送方案. 该方案有多个接收者,通过控制引进辅助粒子数,可以任意调节传送后的纠缠态在各接收者之间的粒子数分布, 且成功传送的概率为1. 关键词： 量子隐形传态 纠缠态 量子通道     

Dephasing and the steady state in quantum many-particle systems

We discuss relaxation in bosonic and fermionic many-particle systems. For integrable systems, time evolution can cause a dephasing effect, leading for finite subsystems to steady states. We explicitly derive those steady subsystem states and devise sufficient prerequisites for the dephasing to occur. We also find simple scenarios, in which dephasing is ineffective and discuss the dependence on dimensionality and criticality. It follows further that, after a quench of system parameters, entanglement entropy will become extensive. This provides a way of creating strong entanglement in a controlled fashion.