囚禁离子与调制热库相互作用时的退相干特征

解析地分析了在囚禁离子中由热库导致量子退相干的控制问题,提出了一个基于热库调制的抑制退相干的一般方法.热库的调制可利用外加的光场与离子相互作用来实现.应用这个方法,适当地选择热库调制参数,可以有效消除量子退相干.计算表明:在高的调制频率下,用这个机制来抑制退相干的效果与宇称激励机制相似.宇称激励机制不仅要求外场是±π脉冲而且要求脉冲既快又强,而热库调制机制仅要求外场频率足够高,因此,热库调制机制优于宇称激励机制.     

制备囚禁冷离子的振动压缩量子态

基于非Lamb-Dicke近似下激光-离子相互作用的动力学规律,讨论了如何利用一系列的激光脉冲来驱动囚禁冷离子.从囚禁冷离子的运动基态出发获得压缩相干态、压缩奇偶相干态、压缩真空态等一系列的振动数态的叠加态.结果表明,只要适当地调节各个所用激光脉冲的长度和相位,总能很好逼近所需要的压缩量子态. 关键词： 囚禁冷离子 激光脉冲 压缩量子态     

二能级系统自发辐射的动力学抑制

研究了在二能级原子系统中有环境诱导的退相干的控制问题.通过对量子位系统施加适当的扰动可以减少由自发辐射引起的退相干.本文提出了一种新的基于频率位移技术和宇称反演技术的机制.这种机制可由两束均匀经典大失谐光场作用于原子来实现.通过应用这种机制,在存在自发辐射的情况下,可以有效地抑制退相干.     

多能级系统中的动力学解耦

动力学解耦技术能有效地抑制由低频环境噪声导致的退相干过程,因此在量子信息领域获得了广泛的应用.传统的动力学解耦方案通过对简单的二能级体系,如量子比特,施加特定的π脉冲序列来实现解耦效果.随着量子计算研发的深入,对于像超导量子比特这种天然的多能级系统,研究者不再局限于二能级子空间,而是提出和实现了一系列基于多能级体系的量子调控手段和量子算法.目前对于如何抑制这些体系中的退相干尚缺乏深入研究.本文利用较易在实验中实现的紧邻能级间的π脉冲,构建了多种针对多能级系统的动力学解耦序列.结果表明这些序列可以很好地消除准静态噪声的影响.此外,通过计算滤波函数,还分析了这些序列及其拓展方案对于高斯噪声的抑制作用,并结合控制函数对滤波效果给出了物理解释.研究结果对于多能级体系中的相关噪声研究,包括噪声功率谱密度和关联性的刻画以及退相干的抑制等,均具有启发意义.     

不同波形脉冲激光的时域误差对相干合成的影响

相干合成技术是实现高功率、高亮度光纤激光系统的重要技术途径.然而, 脉冲激光阵列中常常存在时域误差,这将影响脉冲激光的相干合成效果. 建立了脉冲激光存在时域误差时的相干合成理论模型,并在不同波形(方波、三角波、正弦波) 的脉冲激光存在时域误差时,对相干合成光束在远场的脉冲波形、峰值功率、 光强分布和桶中功率(PIB)等特性进行了数值计算和对比分析.计算结果表明: 方波脉冲激光相干合成光束的脉冲波形受时域误差影响严重,光强分布和PIB随着时域误差 的增大发生线性变化;三角波脉冲激光相干合成光束的脉冲波形和峰值功率受时域误差 影响严重,光强分布和PIB在时域误差较大时随着时域误差的增大发生较为剧烈的变化; 正弦波脉冲激光相干合成光束具有较好的输出特性,在两路正弦波脉冲激光相干合成中, 将两脉冲之间的时延控制在脉冲持续时间的10%以内,就能取得良好的合成效果.     

超导量子比特中的量子跳跃方法

量子力学自建立以来很长一段时间被当作是描述系综运动的理论。但是上世纪80年代对囚禁离子和原子的研究观测到了量子跳跃现象,迫使人们发展了一些能够用于单量子系统的方法,其中之一就是量子跳跃方法。本文总结了我们近来把量子跳跃方法应用到以约瑟夫森隧道结为基础的超导量子比特的工作。我们不但实验观测到宏观量子系统中的量子跳跃,还可以利用量子跳跃现象来研究固体中普遍存在的两能级系统及其引起的超导量子比特中的退相干。     

驻波激光场中囚禁离子的线性熵和量子态转移研究

运用量子纠缠和线性熵理论,研究了驻波激光场中囚禁离子的线性熵和量子态转移.讨论了相干角、离子的相对位相、离子与驻波激光场之间的耦合强度以及失谐量、Lamb-Dicke参数对离子线性熵的影响.结果表明,在一定的条件下可以实现囚禁离子的内态到振动态的相干转移,线性熵随时间的演化呈现非周期性的振荡行为.离子线性熵的最大值随着相干角、离子与激光场之间的耦合强度以及失谐量的增大而减小,随着Lamb-Dicke参数的增大而增大.并且可以通过调节驻波激光场来调节离子与驻波激光场之间的耦合强度和失谐量,从而达到对离子线性熵的控制与操纵,理论上提供了一种调控纠缠的方式.     

基于平衡光学互相关方法的超短脉冲激光相干合成技术

相干合成技术是超快光学领域的重要研究方向之一.当单路脉冲激光的连续谱超过一个倍频程时,精确控制其光谱相位(色散管理)是获得亚周期超短脉冲激光的关键.由于常见的脉冲压缩系统存在光谱带宽限制,因此多通道相干合成技术受到了广泛的关注.本文将充气空心光纤展宽后的超倍频程连续光谱分波段独立压缩,并利用平衡光学互相关方法锁定子脉冲之间的相位延迟,获得了4.1 fs的合成脉冲.实验结果表明相干合成技术在高能量亚周期超快光场调控中存在优势.     

N个热囚禁离子的GHZ态的制备

我们提出了一个简单的方法产生N个囚禁离子的GHZ态.在这个方法中,初始时处于相同态的N个两能级离子被囚禁在一个线性阱中,同时被两束均匀的经典激光照射.这个方法对振动模的加热不敏感,从退相干的观点来看这点很重要.     

强光场下非共振双光子跃迁相干控制

利用飞秒激光脉冲相位整形技术,从理论和实验两方面,对强激光场下分子体系苝溶液中非共振双光子跃迁的相干控制进行了研究。通过对飞秒激光脉冲进行相位扫描和余弦相位调制,发现分子体系中非共振双光子的跃迁几率能够被削弱,但不能完全消除。分子体系中非共振双光子跃迁的相干控制受到激光光场的形状和分子吸收谱谱宽的影响;与原子体系相比,分子体系中非共振双光子跃迁相干控制的调制效率降低。     

Dynamical Suppression of Pure Amplitude Damping in Two-State Quantum Systems

Dynamical control of decoherence induced by the environment in a single quantum-bit system is investigated. We choose the suitable perturbations acting on the qubit system to decrease the decoherence due to pure amplitude damping. The scheme proposed here is based on the free-Hamiltonian-elimination technique and the paritykick technique, which concludes two homogeneous classical large-blue-detuned optical fields with different frequencies added to the qubit system. By applying this scheme, the decoherence can be completely suppressed.     

Dynamical Suppression of Pure Amplitude Damping in Two-State Quantum Systems

Dynamical control of decoherence induced by the environment in a single quantum-bit system is investigated. We choose the suitable perturbations acting on the qubit system to decrease the decoherence due to pure amplitude damping. The scheme proposed here is based on the free-Hamiltonian-elimination technique and the paritykick technique, which concludes two homogeneous classical large-blue-detuned optical fields with different frequencies added to the qubit system. By applying this scheme, the decoherence can be completely suppressed.     

Brun-Type Formalism for Decoherence in Two-Dimensional Quantum Walks

We study decoherence in the quantum walk on the xy-plane.We generalize the method of decoherent coin quantum walk,introduced by [T.A.Brun,et al.,Phys.Rev.A 67(2003) 032304],which could be applicable to all sorts of decoherence in two-dimensional quantum walks,irrespective of the unitary transformation governing the walk.As an application we study decoherence in the presence of broken line noise in which the quantum walk is governed by the two-dimensional Hadamard operator.     

The Self-Induced Approach to Decoherence in Cosmology

In this paper we will present the self-induced approach to decoherence, which does not require the interaction between the system and the environment: decoherence in closed quantum systems is possible. This fact has relevant consequences in cosmology, where the aim is to explain the emergence of classicality in the universe conceived as a closed (noninteracting) quantum system. In particular, we will show that the self-induced approach may be used for describing the evolution of a closed quantum universe, whose classical behavior arises as a result of decoherence.     

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.     

Inflationary Spectra,Decoherence, and Two-Mode Coherent States

We re-examine the question of the entropy stored in the distribution of primordial density fluctuations. To this end we make use of two-mode coherent states. These states incorporate the isotropy of the distribution as well as the temporal coherence and the semi-classical character of highly amplified modes. They also provide a lower bound for the entropy if, as one expects, decoherence processes erase the quantum squeezing which originally characterized the distribution in inflationary models. This lower bound is one half the maximal (thermal) value. By considering backreaction effects, we also provide an upper bound for this entropy at the onset of the adiabatic era.     

The Exact Solution of Milburn Equation Without Diffusion Approximation for the Two-Model Raman Coupled Model

By making use of the dynamical algebraic approach, we study the two-mode Raman coupled model governed by the Milburn equation and find the exact solution of the Milburn equation without diffusion approximation. The exact solution is then used to discuss the influence of intrinsic decoherence on the revivals of atomic inversion, oscillation of the photon number distribution and squeezing of radiation field in the whole ranges of the decoherence parameter γ.     

基于超导量子比特的电磁感应透明研究进展

超导量子计算是目前被认为最有希望实现量子计算机的方案之一. 超导量子比特是超导量子计算的核心部件. 如何尽可能的增加超导量子比特的退相干时间, 大规模的集成超导量子比特已成为超导量子计算研究的主要方向. 超导量子比特作为宏观的人工原子, 有许多量子光学现象都能够在其中观测到. 利用超导量子比特实现电磁感应透明为研究超导量子比特的退相干机理提供了新手段, 为研究非线性光学、光存储、光的超慢速传输等量子光学效应开辟了新思路. 本文介绍了电磁感应透明的理论基础, 总结了目前针对超导量子比特的电磁感应透明研究进展, 对比了一般气体原子与超导量子比特的电磁感应透明区别, 并对超导量子比特实现电磁感应透明的潜在应用进行了总结和展望.