强热辐射环境中两能级原子量子态保真度

两个两能级原子置于强热辐射场环境中，原子用泡利算符描述，环境用无穷的谐振子热库描述，运用密度矩阵方法，得到两能级原子密度矩阵元演化规律.针对三种不同的初始状态，分析置于热辐射场中原子量子态保真度.结果表明：当两个原子初始处于不同量子叠加态时，量子信息在传输过程中可能发生部分失真，也可能不失真. 关键词： 热辐射场 两能级原子 保真度 消相干     

耗散腔中两二能级原子态的量子信息保真度

在能量耗散腔中,原子用泡利算符描述,光场用相干态描述,运用密度矩阵理论,得到了两二能级原子密度矩阵元的演化规律,针对不同的初态,分析与单模辐射场作用过程中原子态的量子信息保真度.结果表明:当两原子初始处于不同的量子态时,量子信息在传输过程中可能不失真或部分失真,也可能出现周期性演化;在输出态和输入态具有相同的纠缠度时,量子信息可能不失真,也可能完全失真.     

耗散腔中两二能级原子态的量子信息保真度

在能量耗散腔中,原子用泡利算符描述,光场用相干态描述,运用密度矩阵理论,得到了两二能级原子密度矩阵元的演化规律,针对不同的初态,分析与单模辐射场作用过程中原子态的量子信息保真度.结果表明:当两原子初始处于不同的量子态时,量子信息在传输过程中可能不失真或部分失真,也可能出现周期性演化;在输出态和输入态具有相同的纠缠度时,量子信息可能不失真,也可能完全失真.     

热辐射中存在偶极相互作用的原子量子态保真度研究

建立了两个两能级原子置于热辐射场环境中的模型,当计及原子偶极间的相互作用时,利用密度矩阵方法,得到两能级原子密度矩阵元随时间的演化规律.针对三种不同的初始状态,分析置于强热辐射场中原子量子态保真度.结果表明:两个原子初始处于不同量子叠加态,量子信息在传输过程中可能发生部分失真,也可能不失真.初始状态对量子信息失真的快慢程度有明显的影响.     

与双模场依赖强度耦合下多光子通道中原子比 特周期量子回声产生和调控

旋波近似条件下,运用全量子理论研究了与双模相干光场依赖强度耦合多光子通道中原子比特周期量子回声的产生和控制. 采用数值计算的方法,讨论了双模相干光场平均光子数分布形式、分布范围及原子跃迁时吸收(或发射)的光子数k对原子比特态保真度演化的影响,获得了产生和控制原子比特周期量子回声的系统参量;根据纠缠理论,分析了原子比特态保真度演化与原子约化熵演化的关联. 结果表明:在k=1的双光子过程中,调控光场平均光子数呈对称或不对称分布,当它的取值在一定范围内,原子比特保持良好的相干性和保真度,产生周期量子回声; 对于k≥2的多光子过程,原子比特与双模相干光场始终处于最大纠缠,因此导致了原子比特始终处于部分失真状态,不产生周期量子回声. 本研究揭示了周期量子回声产生的物理实质是原子比特与光场周期性退纠缠.     

非线性相干态光场与二能级原子相互作用系统的保真度

借助于数值计算的方法,研究了非线性相干态光场与一个二能级原子的相互作用系统保真度的变化规律.讨论了不同的原子初态和光场参量α以及Lamb-Dicke参数η对系统和光场保真度的影响.结果表明,选择合适的参量,我们可以找到保真度平均值较大,振荡幅度较小的光场态.如果我们把光场看作量子信息载体,寻找到保真度高的非线性相干态就是找到了抗干扰能力强的量子态,这在量子通信过程中具有极大的应用价值.     

囚禁离子非线性J-C模型量子态保真度

用全量子理论研究驻波激光场与囚禁离子相互作用系统中量子态保真度,详细讨论离子质心在驻波激光场中位置及离子初始状态对保真度的影响.结果表明:随着囚禁离子从远离驻波激光场波节处向波节处移动,量子态保真度振荡频率越来越高,振荡幅度几乎不变,且保真度到达第一个极小值所用时间越来越短,但不会出现信息完全失真;随着囚禁离子处于基态概率增加,量子态保真度振荡频率几乎不变,振荡幅度越来越小,也不会出现信息完全失真;在信息储存或传递过程中,囚禁离子量子态失真比系统和驻波场量子态失真小.     

两能级原子与热辐射场Raman相互作用时原子量子态保真度

两个两能级原子置于热辐射场环境中,原子用泡利算符描述,环境用无穷的谐振子热库描述.原子与热库产生Raman相互作用,原子间存在偶极相互作用,运用密度矩阵方法,得到两能级原子密度矩阵元演化规律.针对四种不同的初始状态,分析置于热辐射场中原子量子态保真度.结果表明:两个原子初始处于不同量子叠加态,量子信息在传输过程中的保真度有明显的差异.     

量子纠缠消相干对确定型远程制备的影响

研究了两种典型的量子纠缠消相干现象对确定型量子态远程制备方案的影响.首先对该确定型远程制备方案进行了分析,得到该方案确定性和比特消耗情况; 然后通过分析制备过程中纠缠消相干现象对系统的影响得出: 在极化消相干过程中,该系统保真度与目标量子比特在Bloch球上的经度选择无关,仅与目标比特的纬度和消相干的大小有关;在相位消相干中,该系统的保真度不会受到消相干的影响,仅与目标量子态的纬度相关. 关键词： 远程制备 纠缠消相干 通信消耗 保真度     

利用纠缠交换在理想和非理想条件下的远程态制备(英文)

提出了利用纠缠交换技术实现一个纠缠态的远程制备.考虑在量子信道没有遭受噪声影响的条件下,利用一对两粒子纠缠态作为量子信道去实现远程态制备.此外我们考察了噪声存在时的远程态的制备,研究显示不同类型的量子噪声对远程态制备过程的保真度的影响不同.对一个确定量子态,我们考察了消相干效应对其远程制备的影响.     

耗散腔中两二能级原子态的自旋压缩,量子Fisher信息和最大自旋涨落

在能量耗散腔中,原子用泡利算符描述,光场用相干态描述,运用密度矩阵理论,得到了两二能级原子密度矩阵元的演化规律,分析了与单模辐射场作用过程中原子态的自旋压缩、量子Fisher信息和最大自旋涨落.结果表明:自旋压缩,大于 的最大自旋涨落可以作为量子纠缠的充分必要判据.自旋压缩, 大于 的最大自旋涨落和量子纠缠,它们互相等价.大于1的Fisher信息与它们之间没有等价关系,但可以作为自旋压缩和量子纠缠的充分判据.     

耗散腔中两二能级原子态的自旋压缩量子Fisher信息和最大自旋涨落

在能量耗散腔中,原子用泡利算符描述,光场用相干态描述,运用密度矩阵理论,得到了两二能级原子密度矩阵元的演化规律,分析了与单模辐射场作用过程中原子态的自旋压缩、量子Fisher信息和最大自旋涨落.结果表明:自旋压缩,大于1/2的最大自旋涨落可以作为量子纠缠的充分必要判据.自旋压缩,大于1/2的最大自旋涨落和量子纠缠,它们互相等价.大于1的Fisher信息与它们之间没有等价关系,但可以作为自旋压缩和量子纠缠的充分判据.     

Quantum fidelity of Gaussian states in open systems

Using the expression of the fidelity for the most general Gaussian quantum states, the behaviour of the quantum fidelity is described for the states of a harmonic oscillator interacting with an environment, in particular with a thermal bath. By taking a correlated squeezed Gaussian state as initial state, we calculate the quantum fidelity for both kinds of undisplaced and displaced states, and for different values of the squeezing and correlation parameters and of the environment temperature.     

Quantum fidelity for Gaussian states describing the evolution of open systems

Using the expression of the fidelity for the most general Gaussian quantum states, the quantum fidelity is studied for the states of a harmonic oscillator interacting with an environment, in particular with a thermal bath. The time evolution of the considered system is described in the framework of the theory of open systems based on quantum dynamical semigroups. By taking a correlated squeezed Gaussian state as initial state, we calculate the quantum fidelity for both undisplaced and displaced states. The time evolution of the quantum fidelity is analyzed depending on the squeezing and correlation parameters characterizing the initial Gaussian state and on the dissipation constant and temperature of the thermal bath.     

Transition to sub-Planck structures through the superposition of q-oscillator stationary states

We investigate the superposition of four different quantum states based on the q-oscillator. These quantum states are expressed by means of Rogers-Szegö polynomials. We show that such a superposition has the properties of the quantum harmonic oscillator when q→1, and those of a compass state with the appearance of chessboard-type interference patterns when q→0.     

A single-point measurement scheme for quantum work based on the squeezing state

To investigate the role of initial quantum coherence in work-probability distribution, it is necessary to consider an incomplete or partial measurement, in which the energy cannot be fully discriminated by the detector. In this paper, we use a harmonic oscillator with a coherent or squeezing state to realize this incomplete or partial measurement, and propose a unified framework of quantum work statistics for a closed system with an arbitrary initial state. We find that work is proportional to the change of the real part of the coherent state parameter, i.e., quantum work can be estimated by the coherent state parameter. The resulting work-probability distribution includes the initial quantum coherence, and can be reduced to the result of the traditional two projective energy measurement scheme(TPM) by squeezing the state of the harmonic oscillator. Our measurement scheme reveals the fundamental connections between measurement error and coherent work. By introducing a ‘coherent work-to-noise ratio', we find the optimal measurement error, which is determined by the energy difference between the superposed energy levels. As an application, we consider a driven two-level system and investigate the effects of driving velocity on work statistics. We find that only when the driving velocity matches the transition frequency of the system can initial quantum coherence play an important role.     

Enhancement of feasibility of macroscopic quantum superposition state with the quantum Rabi-Stark model

We propose an efficient scheme to generate a macroscopical quantum superposition state with a cavity optomechanical system, which is composed of a quantum Rabi-Stark model coupling to a mechanical oscillator. In a low-energy subspace of the Rabi-Stark model, the dressed states and then the effective Hamiltonian of the system are given. Due to the coupling of the mechanical oscillator and the atom-cavity system, if the initial state of the atom-cavity system is one of the dressed states, the mechanical oscillator will evolve into a corresponding coherent state. Thus, if the initial state of the atom-cavity system is a superposition of two dressed states, a coherent state superposition of the mechanical oscillator can be generated. The quantum coherence and their distinguishable properties of the two coherent states are exhibited by Wigner distribution. We show that the Stark term can enhance significantly the feasibility and quantum coherence of the generated macroscopic quantum superposition state of the oscillator.     

The driven-oscillator evolution in the tomographic-probability representation

We consider the problem of the driven harmonic oscillator in the probability representation of quantum mechanics, where the oscillator states are described by fair nonnegative probability distributions of position measured in rotated and squeezed reference frames in the system??s phase space. For some specific oscillator states like coherent states and nth excited states, the tomographic-probability distributions (called the state tomograms) are found in an explicit form. The evolution equation for the tomograms is discussed for the classical and quantum driven oscillators, and the tomographic propagator for this equation is studied.     

Coherent States and Modified de Broglie-Bohm Complex Quantum Trajectories

This paper examines the nature of classical correspondence in the case of coherent states at the level of quantum trajectories. We first show that for a harmonic oscillator, the coherent state complex quantum trajectories and the complex classical trajectories are identical to each other. This congruence in the complex plane, not restricted to high quantum numbers alone, illustrates that the harmonic oscillator in a coherent state executes classical motion. The quantum trajectories we consider are those conceived in a modified de Broglie-Bohm scheme. Though quantum trajectory representations are widely discussed in recent years, identical classical and quantum trajectories for coherent states are obtained only in the present approach. We may note that this result for standard harmonic oscillator coherent states is not totally unexpected because of their holomorphic nature. The study is extended to coherent states of a particle in an infinite potential well and that in a symmetric Poschl-Teller potential by solving for the trajectories numerically. For the Gazeau-Klauder coherent state of the infinite potential well, almost identical classical and quantum trajectories are obtained whereas for the Poschl-Teller potential, though classical trajectories are not regained, a periodic motion results as t→∞. Similar features were found for the SUSY quantum mechanics-based coherent states of the Poschl-Teller potential too, but this time the pattern of complex trajectories is quite different from that of the previous case. Thus we find that the method is a potential tool in analyzing the properties of generalized coherent states.