混沌原子核系统的相干态描述

当前，人们对量子混沌系统的能谱统计性质的了解比对其波函数性质的了解多得多．通过研究哈密顿系统初始状态为相干量子状态时的传播性质、位置与动量的平均值随时间的演化及涨落的变化性质，将给出系统波函数及相空间分布的信息，并自然给出量子、经典的对应．从理论形式上给出了哈密顿系统状态的相干态表示． So far the statistical fluctuation property of the energy spectrum and its rigidity for quantum chaotic systems are known much more than the wave functions. The study of the propagating property of a quantum state of a Hamiltonian system with its initial state being a coherent state, the time evolution of the mean position and mean momentum, as well as the variation of the position and momentum fluctuation of the system will offer information about the wave function and the phase...     

Dicke模型的量子混沌和单粒子相干动力学特性

量子化的Dicke模型在非旋波近似条件下表现为量子混沌动力学特征.利用单粒子一阶时间关联函数,通过数值计算详细考察了Dicke模型中单粒子相干动力学特性.结果表明:当初始相干态处在混沌区域时,一阶时间关联函数曲线衰减较快,而当初始相干态处在规则区域时,一阶时间关联函数曲线衰减较慢,单粒子相干动力学对初态具有较强的敏感性,经典混沌抑制量子相干.考察单粒子相干动力学在相空间的平均演化性质,得到一种较好的量子经典对应关系.最后研究了相空间单粒子相干的整体动力学性质,更好地揭示了相空间的混沌和规则结构.     

磁场引起的近藤单态退相干机制

磁场作为一个环境能够诱导近藤单态的退相干。我们采用格林函数方法,计算磁场下量子点耦合Aharonov-Bohm环系统的退相干特性,数值结果显示磁场引起的近藤单态的退相干是一个突然的过程。     

原子分子光子系统的耗散相互作用和退相干

原子分子系统与量子化的电磁场或光子模式耦合的系统是非相对论量子力学理论研究和实验研究的主要对象和模型. 现实系统必然与外界环境耦合,且即便原子隔绝较好、光学腔壁品质因子足够高,原子系统也不等价于少数几个能级构成的简单模型：它仍然有不为零的几率跃迁到不可控的能级空间、与原子相互作用的自由空间真空场的量子效应也必须考虑. 本文将结合开放量子系统理论的基本要素与原子光子的基本模型,对原子分子系统在电磁场中发生的耗散以及量子退相干过程做简单综述,并重点介绍描述量子系统退相干过程的主流理论工具——主方程.     

量子相干

量子相干不仅是量子力学中的一个基本概念,同时也是重要的量子信息处理的物理资源.随着基于资源理论框架的量子相干度量方案的提出,量子相干度的量化研究成为近年来人们关注的一个热点问题.量子相干作为一种物理资源也十分脆弱,极容易受到环境噪声的影响而产生退相干,因此开放系统中的量子相干演化和保持也是人们广泛关注的课题.另外,量子相干在量子多体系统、量子热动力学、量子生物学等领域也有着潜在的应用价值.本文介绍量子相干度量的资源理论框架和基于该框架定义的相对熵相干性、l1范数相干性、基于量子纠缠的相干性、基于凸顶结构的相干性和相干鲁棒性等量子相干度量函数,概述开放系统中量子相干演化的动力学行为、典型信道的量子相干产生和破坏能力以及量子相干的冻结等现象,同时例举量子相干在Deutsch-Jozsa算法、Grover算法以及量子多体系统相变问题研究等方面的重要应用.量子相干研究仍处于快速发展之中,期望本综述能为该领域的发展带来启示.     

腔场初始态对两量子比特空间退相干的影响

研究了两个二能级原子与一个单模腔场的相互作用中,腔场的不同初始态对原子间相对位置退相干的影响。从描述原子间相对位置状态的约化密度矩阵出发,假设原子间相对位置为两个高斯波包的叠加态,讨论了当腔场初始态分别为热态、Fock态和压缩态情况下,原子与光场的相互作用对两原子间相对位置相干性的影响。发现腔场的初始态不同,原子间相对位置的退相干情况有所不同。当腔场初始态为热态或Fock态时,原子间相对位置的相干性会周期性的衰减和回复,而当腔场初始态为压缩态时,原子间相对位置会出现部分退相干,且退相干程度与原子间相对位置的大小成余弦变化关系。     

量子点腔非谐振耦合系统纯退相干的特性及应用

采用非相干泵浦、受激辐射和纯退相干的量子主方程研究了量子点腔耦合系统,得出腔与量子点发射光谱解析解.理论分析显示,在非谐振耦合系统中纯退相干能使腔发射谱产生明显的移位效应,从而可以解释"非谐振耦合腔有效发射"效应.为了进一步研究纯退相干在量子点腔耦合系统上的应用,引入了系统有效耦合率和单光子源效率,并通过比较有效耦合率...     

量子点腔非谐振耦合系统纯退相干的特性及应用

采用非相干泵浦、受激辐射和纯退相干的量子主方程研究了量子点腔耦合系统,得出腔与量子点发射光谱解析解.理论分析显示,在非谐振耦合系统中纯退相干能使腔发射谱产生明显的移位效应,从而可以解释“非谐振耦合腔有效发射”效应.为了进一步研究纯退相干在量子点腔耦合系统上的应用,引入了系统有效耦合率和单光子源效率,并通过比较有效耦合率与腔耗散定义出好腔与坏腔机制.选取两组依据实验数据作为参量,在共振与失谐时研究了纯退相干对系统有效耦合率和单光子源效率的影响.结果表明:纯退相干可提高失谐系统有效耦合率与单光子源效率,从而可能使坏腔转变为好腔|两组参量中有较大耦合效率一组在一定范围内满足好腔机制,其单光子源效率明显优于另一组.在非谐振耦合系统比较了好腔机制与坏腔机制的激光,好腔机制是实现单量子点激光的必要条件|由于非谐振耦合系统Fano因子无最大值出现,从而该系统可能无激光阈值.     

三量子位系统的消相干和退纠缠

基于多谐振子热库环境模型,采用求解非马尔可夫近似主方程方法,研究了三量子位系统由于相对位相变化引起的消相干和退纠缠.计算得到了初始态为GHZ-class态、W-class态和WGHZ-class态在演化过程中的消相干和退纠缠时间尺度.结果表明,对初始GHZ-class态,相干性全部丧失,退纠缠完全发生,纠缠度变为0;对初始W-class态,相干性和纠缠度被保持;对初始WGHZ-class态,消相干部分发生,纠缠首先随时间变化最后达到一个渐近值.     

半导体量子点中浸润层跃迁与纯失相对Rabi振荡退相干的影响

理论上分析了半导体量子点中浸润层跃迁(包括泄漏和俘获两个过程)对Rabi振荡退相干的影响,含浸润层跃迁的粒子数运动方程可以很好地拟合实验结果.同时还对比分析了纯失相(pure dephasing)对Rabi振荡退相干的影响.分析表明,可以用简单的纯失相强度相关衰减因子来等效地分析复杂的多能级跃迁体系的退相干特性.     

Quantum to Classical Transition in a System of Two Coupled Kicked Rotors

We investigate the quantum-classical transition in a system of two coupled kicked rotors. We lind that when the mass of one kicked rotor is much smaller than the other＇s, the influence of the light kicked rotor is still able to make decoherence of the heavy one. This leads to the quantum-classical transition of the heavy kicked rotor. We demonstrate this by two different coupling potentials.     

Conditions for Collective Decoherence

An efficient decoherence-reducing strategy exists if two qubits can be made decohered collectively. This paper serves to derive the explicit conditions for coJJective decoherence from a practical decoherence model. We describe two kinds of collective decoherence. In each case, a corresponding decoherence-reducing strategy is proposed.     

Decoherence from a spin chain with Dzyaloshinskii—Moriya interaction

We study the dynamics of quantum discord and entanglement for two spin qubits coupled to a spin chain with Dzyaloshinsky-Moriya interaction.In the case of a two-qubit with an initial pure state,quantum correlations decay to zero at the critical point of the environment in a very short time.In the case of a two-qubit with initial mixed state,it is found that quantum discord may get maximized due to the quantum critical behavior of the environment,while entanglement vanishes under the same condition.Besides,we observed a sudden transition between classical and quantum decoherence when only a single qubit interacts with the environment.The effects of Dzyaloshinsky-Moriya interaction on quantum correlations are considered in the two cases.The decay of quantum correlations is always strengthened by Dzyaloshinsky-Moriya interaction.     

Algebraic Formulation of Quantum Decoherence

An algebraic formalism for quantum decoherence in systems with continuous evolution spectrum is introduced. A certain subalgebra, dense in the characteristic algebra of the system, is defined in such a way that Riemann–Lebesgue theorem can be used to explain decoherence in a well defined final pointer basis.     

Effect of Decoherence Induced by a Spin Environment on Quantum Channel Capacity

We investigate the effect of decoherence from a spin environment on the quantum channel capacity.Our results imply that the time evolution of the quantum channel capacity depends on the number of freedom degrees of the environment,the tunneling element,the initial state of the environment,and the system-environment coupling strength.From the analysis,we find that the strong tunneling elements and the weak coupling strength can enhance the quantum channel capacity while the environment with a large number of freedom degrees and the strong coupling strength will shrink it.     

Dynamics of Optically Driven Exciton and Quantum Decoherence

By using the normal ordering method, we study the state evolution of an optically driven excitons in aquantum well immersed in a leaky cavity, which was introduced by Yu-Xi Liu et al. [Phys. Rev. A63 (2001) 033816]. Theinfluence of the externallaser field on the quantum decoherence of a mesoscopically superposed state of the excitons isinvestigated. Our result shows that, the classical field can compensate the energy dissipation of the excitons. Althoughthe decoherence rate of the excitonic Schrodinger cat state does not depend on the external field, the phase of thedecoherence factor can be well controlled by adjusting the amplitude of the external field as well as the detuning betweenthe field and the transition frequency of the atom.     

Frequently Asked Questions About Decoherence

We give a short, critical review of the issue of decoherence. We establish the most general framework in which decoherence can be discussed, how it can be quantified, and how it can be measured. We focus on environment induced decoherence and its degree of usefulness for the interpretation of quantum theory. We finally discuss the emergence of a classical world. An overall emphasis is given in pointing at common fallacies and misconceptions.     

Energy basis via decoherence

The question of the emergence of a preferred basis which is generally understood as that basis in which the reduced density matrix is driven to a diagonal (classically interpretable) form via environment induced decoherence is addressed. The exact solutions of the Caldeira-Leggett Master Equation are analyzed for a free particle and a harmonic oscillator system. In both cases, we see that the reduced density matrix is driven diagonal in the energy basis, which is momentum for the free particle and the number states for the harmonic oscillator. This seems to single out the energy basis as the preferred basis which is contrary to the general notion that it is the position basis which is selected since the coupling to the environment is via the position coordinates     

消干效应和量子力学新解释的意义

简单介绍了消干 (decoherence)效应以及量子力学的一种新解释———由Griffiths,Gell Mann和Omn埁ｓ等独立提出的“消干历史解释”的由来和要点 ,评述了这一进展在量子理论发展中的意义 .