量子算法与量子计算实验

从量子体系的基本特性出发 ,介绍了量子计算的基本概念和物理背景 ,系统阐述了几种主要的量子算法以及量子计算在实验方面的发展现状。对比经典计算机 ,讨论了量子计算机的优越性、实现量子计算的困难和以期克服的途径。     

Irreversibility of a quantum walk induced by controllable decoherence employing random unitary operations

Quantum walk is different from random walk in reversibility and interference. Observation of the reduced re- versibility in a realistic quantum walk is of scientific interest in understanding the unique quantum behavior. We propose an idea to experimentally investigate the decoherence-induced irreversibility of quantum walks with trapped ions in phase space via the average fidelity decay. By introducing two controllable decoherence sources, i.e., the phase damping channel (i.e., dephasing) and the high temperature amplitude reservoir (i.e., dissipation), in the intervals between the steps of quantum walk, we find that the high temperature amplitude reservoir shows more detrimental effects than the phase damping channel on quantum walks. Our study also shows that the average fidelity decay works better than the position variance for characterizing the transition from quantum walks to random walk. Experimental feasibility to monitor the irreversibility is justified using currently available techniques.     

No Spin-Localization Phase Transition in the Spin-Boson Model without Local Field

We explore the spin-boson model in a special case, i.e., with zero local field. In contrast to previous studies, we find no possibility for quantum phase transition （QPT） happening between the localized and delocalized phases, and the behavior of the model can be fully characterized by the even or odd parity as well as the parity breaking, instead of the QPT, owned by the ground state of the system. The parity breaking mentioned in our case is completely different from the spontaneously broken symmetry relevant to the conventionally defined QPT in previous studies. Our analytical treatment about the eigensolution of the ground state of the model presents for the first time a rigorous proof of no- degeneracy for the ground state of the model, which is independent of the bath type, the degrees of freedom of the bath and the calculation precision. We argue that the QPT mentioned previously appears due to incorrect employment of the ground state of the model and/or unreasonable treatment of the infrared divergence existing in the spectral functions for Ohmic and sub-Ohmic dissipations.     

量子计算与超冷离子

通过介绍量子计算的基本概念和特点，并对比目前人们使用的计算机的计算方式，对于如何利用囚禁在离子阱中的超冷离子进行量子计算作了简要的叙述．     

Paul阱内的压缩效应与量子跃迁

处理一个一维Ｐａｕｌ阱系统中的压缩现象与量子跃迁现象，对于阱内的最强压缩态和共振跃迁（一种极不稳定状态）之间的关系作了阐述，并对利用压缩性质在阱内进行精密测量的可能性作了讨论     

Paul阱中两个超冷离子的量子统计特性

讨论两个囚禁在Ｐａｕｌ阱的对称轴上的超冷离子的量子统计特性，可以发现，它们的稳定囚禁不仅与阱的稳定区有关，而且与它们自身的自旋和电荷数大小有关。     

离子阱中实现两位量子搜寻的方案

该文首先讨论在离子阱中,如何利用红、蓝失谐跃迁来构造量子计算所需的各种幺正矩阵。然后利用这些矩阵提出了一个实现两位量子搜寻的方案。     

Nonclassical Properties of Photon-Added Pair Coherent States

After analyzing the course of forming‘garbageblocks’,we proposed an alternative for preparing the pseudo-pure states.It can be used to reduce or even to remove the‘garbageblocks’.     

核磁共振实现基本量子逻辑门和量子分立付里叶变换

本文详细研究了利用核磁共振方法实现基本量子逻辑操作,提出了实现量子分立付里叶变换的实验方案,设计了可供实验的脉冲系列,为实验研究量子分立付里叶变换提供了具体方案。     

无旋转波近似下单个超冷离子与一束驻波型激光相互作用的动力学

在相互作用表象中,研究了Lamb-Dicke区内单个超冷囚禁离子与一束驻 波型激光相互作用的动力学行为。由于没有引入旋转波近似,离子的运动随着Lamb-Dicke 参数η和Rabi频率Ω的增大趋向于混沌。所得结果与旋转波近似下的结果作了比较 。