利用热纠缠态表象获得Caldeira-Leggett密度算符方程的积分形式解

开放量子系统,即系统-热库模型,可以用一个关于密度算符的主方程来描述,比如,用来描述固态物理中耗散现象的Caldeira.Leggett主方程.虽然已经有人为了求解此主方程的约化密度矩阵的精确表达式而做过一些努力,但迄今还未见有解答.本文使用了一种全新的方法来求解Caldeira-Leggett方程,用这个新方法可以得到积分形式的显式表达.该方法的要点在于利用有序算符内积分技术把关于密度算符的微分方程首先转化成关于密度态矢量的微分方程,再将密度态矢量投影到热纠缠态表象中,Caldeira-Leggett方程就转变成了关于波函数的微分方程,而波函数是函数.这样就可以使用数学中求解微分方程的方法来求解出波函数.再次利用有序算符内积分技术,再将波函数转化为态矢量和算符,就得到了Caldeira-Leggett方程的积分形势解.     

单-双模组合压缩热态的纠缠性质及在量子隐形传态中的应用

基于单-双模组合压缩真空态一定范围内能够获得压缩增强的效果,引入单-双模组合压缩热态(DSMST),讨论其纠缠性质.利用Weyl编序算符在相似变换下的不变性,简洁方便地导出了DSMST的纠缠度-负对数值,并给出了当热效应存在时保持纠缠的条件.研究表明:与通常的双模压缩态相比,随着参数的增加,DSMST的纠缠度增加.作为DSMST的应用,利用其实现相干态的量子隐形传输.结果表明:不同于纠缠度随压缩参数增加,保真度获得改善是有条件的,该条件恰好就是一正交分量涨落出现压缩增强的参数区域.此外,解析推导了有效隐形传输保真度(1/2)的条件.     

压缩真空态中原子与场的量子纠缠和量子discord

在压缩真空库中,研究了原子与场的相互作用下二比特体系的量子discord和量子纠缠的动力学行为.重点分析了原子的初始态系数和压缩真空库的压缩系数对量子纠缠和量子discord的影响.通过数值分析我们得到,随着原子的初始态系数和压缩真空库的压缩系数值的增加,量子纠缠和量子discord都会减小,但量子纠缠比量子discord减小的更快一些.最后研究了在原子的初始态系数和压缩真空库的压缩系数的值相同的情况下,量子discord比量子纠缠存在的时间更长些.     

测量相位算符在压缩热场态中的压缩效应

利用Bannett和Pegg提出的测量相位算符讨论了压缩热场态中测量相位算符的压缩效应。结果表明测量相位算符在压缩热场态中存在CS类压缩，压缩特性与相干态参数幅角θ、平均光子数n^-和压缩参量r有密切的关系。随着n^-和r的增大，CS类压缩效应逐渐减弱，直至完全消失。另有计算表明测量相位算符在压缩热场态中不存在CN和SN类压缩。     

利用原子-腔场喇曼相互作用制备纠缠压缩真空态

提出了利用量子态腔场与原子的喇曼相互作用制备纠缠压缩真空态的方案.在该方案中,一个初始制备在基态的原子被依次送入几个初始制备在压缩真空态的微腔中.通过控制原子的运行速度,使原子与每一个腔具有相同的相互作用时间.当原子与腔场发生相互作用,原子与腔场产生纠缠之后,进行原子的测量.当原子被测量处于基态或激发态时,按照量子力学波包塌缩原理,腔场态将塌缩到相应的纠缠压缩真空态.对纠缠压缩真空态的纠缠性质也进行了简略的讨论.     

介观RLC电路在热真空态下的量子涨落

利用热场动力学的方法研究了介观RLC电路在具有热噪声的真空态下电荷和磁通(电流)的量子涨落.从而得到了有限温度下这一电路在热真空态下的量子涨落与温度的关系.结果表明,介观RLC电路的量子涨落不仅与电路中的元件参量和电路的共振频率ω有关,而且与温度T有关.温度越高,介观RLC电路的量子噪声越大 关键词： 介观RLC电路 热真空态 量子涨落     

走近量子纠缠系列之六 纠缠态及实验

在谈到实验之前,还得顺便提一句,我们在此系列文章中,所谈到的量子纠缠以及推导贝尔不等式的过程,用的都是EPR佯谬简化了的波姆版。也就是说,我们使用了两个不同的自旋("上↑"和"下↓")来表述量子态,这使得问题叙述起来简化很多,因为在这种只有两个离散变量的情况下,单个粒子     

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     

用纠缠态表象讨论对双模压缩真空态作正交振幅分量的测量

对文献[4]的结果作了进一步推导,用纠缠态表象方法计算了对双模压缩真空态第一个模场作正交振幅分量测量的结果,发现第二个模塌缩到一个压缩态,其显式被导出。     

连续变量多组分纠缠态光场及其在量子计算中的应用

在发展基于单光子的量子信息系统的同时,以光场正交分量为基础的连续变量量子信息科学也在蓬勃发展,多组分纠缠态光场是研究连续变量量子计算的基本资源.文章简要介绍了连续变量多组分纠缠态光场的概念和制备方法,以及连续变量量子计算的基本模型和实验研究进展.     

Solving Master Equation for Two-Mode Density Matrices by Virtue of Thermal Entangled State Representation

We extend the approach of solving master equations for density matrices by projecting it onto the thermal entangled state representation (Hong-Yi Fan and Jun-Hua Chen, J. Phys. A35 (2002) 6873) to two-mode case. In this approach the two-photon master equations can be directly and conveniently converted into c-number partial differential equations. As an example, we solve the typical master equation for two-photon process in some limiting cases.     

Solution to Operator Fredholm Equation in Bipartite Entangled State Representation and Its Applications

Based on the bipartite entangled state representation and using the technique of integration within an ordered product （IWOP） of operators we construct the corresponding operator Fredholm equations and then derive their solutions. As its application we deduce some new bosonic operator identities and new relations about the two-variable Hermite polynomials.     

Thermal Wigner Operator in Coherent Thermal State Representation and Its Application

In the coherent thermal state representation we introduce thermal Wigner operator and find that it is “squeezed” under the thermal transformation.The thermal Wigner operator provides us with a new direct and neat approach for deriving Wigner functions of thermal states.     

Hermitian Operators Conjugate to Two-Mode Number-Difference Operator Studied in Entangled State Representation

In similar to the derivation of phase angle operator conjugate to the number operator by Arroyo Carrasco- Moya Cessay we deduce the Hermitian phase operators that are conjugate to the two-mode number-difference operator and the three-mode number combination operator. It is shown that these operators are on the same footing in the entangled state representation as the one of Turski in the coherent state representation.     

Hermitian Operators Conjugate to Two-Mode Number-Difference Operator Studied in Entangled State Representation

In similar to the derivation of phase angle operator conjugate to the number operator by Arroyo Carrasco-Moya Cessay we deduce the Hermitian phase operators that are conjugate to the two-mode number-difference operator and the three-mode number combination operator. It is shown that these operators are on the same footing in the entangled state representation as the one of Turski in the coherent state representation.     

Four-Particle Entangled State Representation and Its Squeezing Transformation

The four-particle EPR entangled state | p,χ₂,χ₃,χ₄〉is constructed. The corresponding quantum mechanical operator with respect to the classical transformation p→e^λ₁p, χ₂→ e^λ₂χ₂, χ₃→e^λ₃χ₃, and χ₄→e^λ₄χ₄ in the state |p,χ₂ ,χ₃ ,χ₄〉is investigated, and the four-mode realization of the SU(1,1) Lie algebra as well as the corresponding squeezing operators are presented.     

Some New Properties of Wigner Function Studied in Entangled State Representation

Based on the Wigner operator in the entangled state representation we study some new important properties of Wigner function for bipartite entangled systems, such as size of an entangled state, upper bound of Wigner functions, etc. These discussions demonstrate the beauty and elegance of the entangled state representation.     

Complex-Variable Fokker-Planck Equation Solved in Entangled State Representation

We lind that the Fokker-Planck equation in complex variables can be conveniently solved in the context of bipartite entangled state representation and its relationship with SU（2） Lie algebraic generators＇ new realization {（1/4）[（Q1 - Q2）^2 ＋ （P1＋ P2）^2], （1/4）[（Q1 ＋Q2）^2＋ （P1 - P2）^2], and -（i/2）（Q1P2 ＋ Q2P1）}, the quadratic combination of canonical operators.     

New Three-Mode Squeezing Operators Gained via Tripartite Entangled State Representation

We show that the Agarwal-Simon representation of single-mode squeezed states can be generalized to find new form of three-mode squeezed states. We use the tripartite entangled state representations ｜p, y, z） and ｜x, u, v） to realize this goal.