二能级系统的马尔可夫与非马尔可夫方法比较

分别用马尔可夫与非马尔可夫方法推导出二能级系统与库相互作用的耗散动力学,并把失谐谱密度与一个光子带隙的谱密度下的计算结果与精确解进行比较。对于失谐谱密度,分别讨论在马尔可夫与非马尔可夫库的激发态布居数,发现无论是短时的弱耦合区域,还是长时间的强耦合区域,非马尔可夫方法比马尔可夫方法更加接近精确解,而马尔可夫近似主要适用于弱耦合条件;对于光子带隙谱密度,主要考虑了小带宽的布居数,结果显示马尔可夫方法主要适用于弱耦合条件,而非马尔可夫方法主要适用于强耦合情形。结果表明:对于不同谱密度、不同的耦合区域,只有选择合适的马尔可夫或非马尔可夫方法才能精确描述系统的动力学。     

二能级系统的马尔可夫与非马尔可夫方法比较

分别用马尔可夫与非马尔可夫方法推导出二能级系统与库相互作用的耗散动力学,并把失谐谱密度与一个光子带隙的谱密度下的计算结果与精确解进行比较。对于失谐谱密度,分别讨论在马尔可夫与非马尔可夫库的激发态布居数,发现无论是短时的弱耦合区域,还是长时间的强耦合区域,非马尔可夫方法比马尔可夫方法更加接近精确解,而马尔可夫近似主要适用于弱耦合条件;对于光子带隙谱密度,主要考虑了小带宽的布居数,结果显示马尔可夫方法主要适用于弱耦合条件,而非马尔可夫方法主要适用于强耦合情形。结果表明：对于不同谱密度、不同的耦合区域,只有选择合适的马尔可夫或非马尔可夫方法才能精确描述系统的动力学。     

二能级量子系统中的Berry相因子

本文详细计算了二能级量子系统中的Ｂｅｒｒｙ相因子，并诠释了它的几何意义，最后以中子极化干涉和激光束通过光纤螺旋管为例说明Ｂｅｒｒｙ相因子的可观察效应     

夹层结构中二能级原子非马尔科夫自发衰减过程的记忆函数

文章研究了夹层结构中二能级原子非马尔科夫自发衰减过程的记忆函数.运用量子光学方法导出了夹层结构中二能级原子的库的耦合谱和非马尔科夫记忆函数.谱中包含了决定谱宽度的权重因子.发现记忆函数控制着原子自发衰减的动力学演化;由于辐射场被夹层结构扰动,记忆函数出现逐渐变弱的抖动:记忆时间依赖于耦合谱的宽度,宽的谱导致短的记忆时间.     

电磁场中二能级原子的量子相干性

求解了经典电磁场中二能级原子系统的密度矩阵演化方程,得到了系统状态的相干特性x     

用外加驱动场压缩有热槽相互作用二态量子系统的退相干性

讨论了具有热槽相互作用二态量子系统在外加驱动场作用下的退相干性问题,推导了二态量子系统密度算子非对角矩阵元的时间演化关系.确定了外加驱动场与退相干性之间的关系,并建立了退相干性消除时外加场必须满足的约束方程. 关键词：     

消除简并双光子过程中二能级原子的消相干性

研究了置于外部环境(热库)中的二能级原子在外加驱动场时原子的消相干问题.得到简并双光子过程中原子约化密度算符非对角元.在二能级原子的消相干被消除的情况下,讨论外加驱动场的特性. 关键词： 简并双光子过程 二能级原子 消相干性     

混合态二能级原子双光子过程的量子特性

采用时间演化算符方法研究了相干光场与混合二能级以光了过程的粒子数反转和光子演化行为，结果表明：量子崩塌与复苏性质和原子实始的混合程度无关，但振荡最大幅值受原子初始混合程度的支配，随着原子初始混合程度的增大，原子反转几率减小，〈ｎ〉的时间平均值下降。     

二能级系统的布居囚禁现象

采用缀饰原子模型,以解析方式研究了二能级系统布居囚禁现象,给出了实现布居囚禁现象的条件,并通过解析公式计算演示了各种条件下布居囚禁的不同行为.所有的解析计算都与数值计算结果相一致. 关键词： 布居囚禁 二能级系统     

单模量子场作用下二能级原子能级的AC Stark移动

通过分析跃迁概率幅的相位给出了与时间相关的微扰在跃迁过程中引起的能级移动公式,计算了处在不同量子态的单模场引起的二能级原子能级的AC Stark移动,结果表明场的量子统计特性会直接影响到原子能级移动. 关键词： AC Stark效应 单模量子场 二能级原子     

Sufficient Conditions of the Same State Order Induced by Coherence

In this paper, we study coherence-induced state ordering with Tsallis relative entropy of coherence, relative entropy of coherence and l₁ norm of coherence, and give the sufficient conditions of the same state order induced by above coherence measures. First, we show that the above measures give the same ordering for single-qubit states in some special cases. Second, we consider some special states in a d-dimensional quantum system. We show that the above measures generate the same ordering for these special states. Finally, we discuss dynamics of coherence-induced state ordering under Markovian channels. We find amplitude damping channel changes the coherence-induced ordering even though for single-qubit states with fixed mixedness.     

Protecting quantum coherence of two-level atoms from vacuum fluctuations of electromagnetic field

In the framework of open quantum systems, we study the dynamics of a static polarizable two-level atom interacting with a bath of fluctuating vacuum electromagnetic field and explore under which conditions the coherence of the open quantum system is unaffected by the environment. For both a single-qubit and two-qubit systems, we find that the quantum coherence cannot be protected from noise when the atom interacts with a non-boundary electromagnetic field. However, with the presence of a boundary, the dynamical conditions for the insusceptible of quantum coherence are fulfilled only when the atom is close to the boundary and is transversely polarizable. Otherwise, the quantum coherence can only be protected in some degree in other polarizable direction.     

与XY双自旋链耦合的双量子比特系统的关联性与相干性

研究了双量子比特系统中在具有Dzyaloshinsky-Moriya相互作用的独立XY自旋链环境下的相干性与关联性动力学.推导出相干性与关联性的演化规律.发现在自旋链的临界点附近,当tt_0时,系统相干性的演化与经典关联完全相同;而在tt_0时,则与量子关联完全相同;在t_0时刻,量子关联突变为经典关联.     

Quantum Non-Markovian Environment-to-System Backflows of Information: Nonoperational vs. Operational Approaches

Quantum memory effects can be qualitatively understood as a consequence of an environment-to-system backflow of information. Here, we analyze and compare how this concept is interpreted and implemented in different approaches to quantum non-Markovianity. We study a nonoperational approach, defined by the distinguishability between two system states characterized by different initial conditions, and an operational approach, which is defined by the correlation between different outcomes associated to successive measurement processes performed over the system of interest. The differences, limitations, and vantages of each approach are characterized in detail by considering diverse system–environment models and dynamics. As a specific example, we study a non-Markovian depolarizing map induced by the interaction of the system of interest with an environment characterized by incoherent and coherent self-dynamics.     

On the response of a two-level quantum system to a class of time-dependent quasiperiodic perturbations

We study analytically the response of a two-level quantum system to a certain class of time-dependent quasiperiodic perturbations generated by a Fibonacci sequence. We show that the quasi-energy spectrum (Fourier transform of the evolution operator) generically is not a denumerable sum of delta functions. Hence the response is not quasiperiodic. Several numerical investigations (Poincaré sections, polarization fluctuation, etc.) suggest an intermediate kind of behavior between quasiperiodic and chaotic.     

非对称自旋-轨道耦合系统的多体量子相干含时演化

本文以具有非对称性自旋相互作用的三体自旋系统为研究对象,重点研究了三体量子相干含时演化规律.采用精确量子对角化和基于量子主方程的数值模拟方法,讨论了三体量子系统中多种量子相干组分及其退相干.研究发现,量子相干组分的含时演化与整个系统的初态量子特性紧密相关.当初态为可分离纯态时,在较短时间内,非对称相互作用有利于增加多体量子相干度.这些量子相干度因受噪声影响而逐渐衰减.当初态为类Werner态时,量子相干度的分布满足加和性,即三体量子相干度等于所有两体量子相干度之和.自旋之间非对称相互作用和环境噪声都会引起三体量子相干度大于所有两体量子相干度之和.这些结论有助于多体量子资源的制备.     

Measure of irreversibility and entropy production in open quantum systems

A new concept of a measure of irreversibility for quantum dynamics in open systems is introduced as a suitably regularized substitute for the common notion of entropy production, which, unfortunately, yields infinite values for so many irreversible processes of physical relevance.     

Quantifying coherence with dynamical discord

Quantum coherence and discord are two kinds of manifestations of nonclassicality. By calculating the coherence and discord in the specific bipartite quantum systems, we show quantitative connections between the coherence and the discord in the bipartite quantum systems created from local systems with the help of incoherent operations. We show that the coherence bounds the dynamical discord, and under particular conditions of the initial quantum states, the coherence of single systems is equal to the dynamical discord. We extend these results to the multipartite quantum systems.     

Entanglement entropy, decoherence, and quantum phase transitions of a dissipative two-level system

The concept of entanglement entropy appears in multiple contexts, from black hole physics to quantum information theory, where it measures the entanglement of quantum states. We investigate the entanglement entropy in a simple model, the spin-boson model, which describes a qubit (two-level system) interacting with a collection of harmonic oscillators that models the environment responsible for decoherence and dissipation. The entanglement entropy allows to make a precise unification between entanglement of the spin with its environment, decoherence, and quantum phase transitions. We derive exact analytical results which are confirmed by Numerical Renormalization Group arguments both for an ohmic and a subohmic bosonic bath. The entanglement entropy obeys universal scalings. We make comparisons with entanglement properties in the quantum Ising model and in the Dicke model. We also emphasize the possibility of measuring this entropy using charge qubits subject to electromagnetic noise; such measurements would provide an empirical proof of the existence of entanglement entropy.     

Entanglement in a system of two two-level atoms interacting with a single-mode field

We investigate the entanglement in a system of two coupling atoms interacting with a single-mode field by means of quantum information entropy theory. The quantum entanglement between the two atoms and the coherent field is discussed by using the quantum reduced entropy, and the entanglement between the two coupling atoms is also investigated by using the quantum relative entropy. In addition, the influences of the atomic dipole--dipole interaction intensity and the average photon number of the coherent field on the degree of the entanglement is examined. The results show that the evolution of the degree of entanglement between the two atoms and the field is just opposite to that of the degree of entanglement between the two atoms. And the properties of the quantum entanglement in the system rely on the atomic dipole--dipole interaction and the average photon number of the coherent field.