Stabilized quantum coherence and remote state preparation in structured environments

The radiation decay of a two-level atom could be inhibited within structured environments even under longtime evolution. We investigate the stabilized quantum coherence of composite systems undergoing local dissipation and exploit it further as a resource for remote state preparation. We focus on outputs of quantum states with solely quantum discord （i.e., without entanglement） and demonstrate that they could be resulted from various initial states providing specific spectral structure of the reservoir. In detail, we elaborate the behavior of stabilized quantum discord and the corresponding fidelity for remote state preparation in connection with structural spectra of Ohmic class reservoir and of photonic band gap mediums.     

利用部分纠缠态确定性实现量子远程态制备

提出了一种利用局域操作和经典通讯经由任一纠缠纯态与辅助纠缠态远程实现量子态制备的方案.该方案由一个广义测量(即正定算符值测量,简称POVM)、单边经典通讯和相应的幺正操作来完成.首先,讨论了两维部分纠缠态作通道的情形,然后将其推广到高维粒子纠缠态的情况.     

量子系统中基于李雅普诺夫稳定性理论的叠加态的制备

在量子系统中利用被控系统的本征值,构造用来进行坐标旋转的幺正矩阵．通过幺正变换操作抵消系统每个状态所具有的局部相位,并选择变换后的被控状态与目标态之间的误差作为李雅普诺夫函数．在此基础上,基于李雅普诺夫稳定性理论,在保证控制系统稳定的前提下进行控制律的设计,给出了系统状态制备所需控制的详细设计过程,并对结果进行了对比分析．最后,在一个自旋1／2粒子系统上,采用本文所提方法分别对目标态是本征态和叠加态的制备进行了系统仿真实验,并对系统状态演化时间与不同参数情况下控制值之间的关系进行了分析．     

量子隐形传态中纠缠态制备的研究进展

量子隐形传态是量子力学和信息科学等形成的交叉课题,同时也是近些年来人们研究的热点之一。文章首先回顾了Bennett等人所提出的量子隐形传态的基本思想和基本原理,然后着重介绍了量子隐形传态中的重要步骤,即量子纠缠态的制备及其在传统上和近年来的一些具有代表性的实验实现方案。     

相干矢量表象中的量子相干性度量

量子相干性度量最近是量子资源理论中的热点任务. Baumgratz等人已经于2014年提出严格的相干性度量框架.在该框架中,相干性度量的定义要求把量子态固定在希尔伯特空间中一组特定基矢上,其结果是在同一度量下,基矢的变换会引起同一量子态的相干性发生改变.在相干矢量表象中利用相干矢量的旋转性质,一种基于相干矢量归一化模长的相干性度量被提出.在该度量中,同一量子态的相干性独立于基矢的选择.基于该度量的非相干态和非相干算符已经分别定义为经典最大混合态和酉算符.同时,三条重要性质已经得到,分别为非负性、凸性和非相干操作不变性.     

控制开放超导量子电路系统中的几何量子关联冻结和量子相干性

本文研究了开放超导量子电路系统中,含时电磁场对两超导量子比特间的几何量子关联和量子相干性的影响. 我们发现,加入磁场之后,几何量子关联被冻结的现象会出现,并且冻结的时间会随着含时电磁场的加入而得到延长. 利用迹距离的方法,我们探讨了含时电磁场对超导量子比特与环境之间量子信息流动的影响,我们发现含时电磁场可以抑制环境的影响,降低超导量子比特与环境之间的量子信息流动.     

利用部分纠缠的量子信道确定性地实现N→1和1→N的受控量子远程旋转

提出利用部分纠缠的量子信道确定性地实现多个发送者1个接受者和1个发送者多个接受者的受控量子远程旋转方案.首先考虑利用两个(N?M?1)粒子部分纠缠的Greenberger-Horne-Zeilinger(GHZ)态确定性地实现N个发送者在M个监控者的控制下确定性地将她们的旋转分别传给远处接受者的操作(N→1).然后考虑在一个(2K?M?1)粒子部分纠缠的Einstein-Podolsky-Rosen(EPR)-GHZ态或K个(M+2)粒子部分纠缠的GHZ态辅助下,发送者随意地将她的旋转分为N份(NK)并在M个监控者的控制下确定性地将它们分别传给远处N个接受者的操作(1→N).方案中,量子旋转的发送者或接受者或监控者的正定算符值测量(POVM)起着关键作用,我们给出了它们的数学表式.值得注意的是,用非理想的量子信道可确定性地实现N→1或1→N的量子远程旋转.这些方案可用于量子秘密共享,量子选举等,它们具极强的保密性.     

Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems

Photosynthetic complexes are exquisitely tuned to capture solar light efficiently, and then transmit the excitation energy to reaction centres, where long term energy storage is initiated. The energy transfer mechanism is often described by semiclassical models that invoke 'hopping' of excited-state populations along discrete energy levels. Two-dimensional Fourier transform electronic spectroscopy has mapped these energy levels and their coupling in the Fenna-Matthews-Olson (FMO) bacteriochlorophyll complex, which is found in green sulphur bacteria and acts as an energy 'wire' connecting a large peripheral light-harvesting antenna, the chlorosome, to the reaction centre. The spectroscopic data clearly document the dependence of the dominant energy transport pathways on the spatial properties of the excited-state wavefunctions of the whole bacteriochlorophyll complex. But the intricate dynamics of quantum coherence, which has no classical analogue, was largely neglected in the analyses-even though electronic energy transfer involving oscillatory populations of donors and acceptors was first discussed more than 70 years ago, and electronic quantum beats arising from quantum coherence in photosynthetic complexes have been predicted and indirectly observed. Here we extend previous two-dimensional electronic spectroscopy investigations of the FMO bacteriochlorophyll complex, and obtain direct evidence for remarkably long-lived electronic quantum coherence playing an important part in energy transfer processes within this system. The quantum coherence manifests itself in characteristic, directly observable quantum beating signals among the excitons within the Chlorobium tepidum FMO complex at 77 K. This wavelike characteristic of the energy transfer within the photosynthetic complex can explain its extreme efficiency, in that it allows the complexes to sample vast areas of phase space to find the most efficient path.     

利用动力学去耦合脉冲增大和调节量子相干性和三体纠缠

本文研究了动力学去耦合脉冲对腔量子电动力学系统中量子相干性, 量子失谐和量子纠缠的影响, 发现动力学去耦合脉冲不仅能够增大系统中两原子之间的量子相干性, 同时也能增大它们之间非经典关联（量子失谐和量子纠缠）. 同时, 凭借迹距离的方法, 探讨了动力学去耦合脉冲增大两原子之间量子相干性的原因, 通过探究可以看出动力学去耦合脉冲能够控制和加速量子信息从其他子系统回流到两个原子中去, 并减少两原子子系统和其他子系统之间的量子信息流动, 从而增加两原子间的量子相干性和非经典关联. 最后, 利用保真度的方法研究了系统中三体纠缠出现的情况, 结果显示在不同的时间, 系统中会出现三体纠缠, 特别值得指出的是, 可以通过动力学去耦合脉冲来调节和增加系统中三体纠缠出现的时间.     

圆柱形半导体量子线中电子和空穴能态

半导体量子线具有特殊的量子效应,其内部电子的能态是它的一个基本物理量.用计算一维势阱波函数的方法简化了圆柱形量子线波函数的计算,得出了量子线中电子能态、能级图和波函数.做算例Si量子线的线宽———电子能级图,验证了计算所得结果,并讨论了量子线的光谱蓝移、能级分离与兼并和线宽的关系.     

Storage and retrieval of single photons transmitted between remote quantum memories

An elementary quantum network operation involves storing a qubit state in an atomic quantum memory node, and then retrieving and transporting the information through a single photon excitation to a remote quantum memory node for further storage or analysis. Implementations of quantum network operations are thus conditioned on the ability to realize matter-to-light and/or light-to-matter quantum state mappings. Here we report the generation, transmission, storage and retrieval of single quanta using two remote atomic ensembles. A single photon is generated from a cold atomic ensemble at one site , and is directed to another site through 100 metres of optical fibre. The photon is then converted into a single collective atomic excitation using a dark-state polariton approach. After a programmable storage time, the atomic excitation is converted back into a single photon. This is demonstrated experimentally, for a storage time of 0.5 microseconds, by measurement of an anti-correlation parameter. Storage times exceeding ten microseconds are observed by intensity cross-correlation measurements. This storage period is two orders of magnitude longer than the time required to achieve conversion between photonic and atomic quanta. The controlled transfer of single quanta between remote quantum memories constitutes an important step towards distributed quantum networks.     

噪声环境下纠缠相干态的量子关联特性

着重研究了在振幅噪声环境下两体纠缠相干态(Entangled Coherent State,ECS)与贝尔态的量子关联演化.用形成纠缠熵(Entanglement of Formation,E)、量子失协(Quantum Discord,QD)、测量诱导扰动(Measurement-Induced Disturbance,MID)及几何量子失协(Geometric Measure of Quantum Discord,GQD)来计算纠缠相干态在噪声环境下的量子关联演化,发现纠缠相干态的量子失协随着r先减小再增长,然后又逐渐衰减至0,其测量诱导扰动则随着r单调衰减到0,而量子失协以及测量诱导的扰动在振幅衰减影响下比形成纠缠熵演化更加持久.通过对比分析,发现对称与非对称噪声通道下贝尔(Bell)态不一定比纠缠相干态的纠缠度更高,纠缠相干态以及贝尔态的量子关联影响区别不是很明显.     

ZnO量子点的制备及其发光特性研究

利用溶胶-凝胶法在乙醇溶液中制备出ZnO量子点。通过紫外-可见吸收光谱(UV-Vis)和荧光光谱对合成量子点的发光性质进行了研究。结果表明,ZnO量子点的荧光光谱由两部分组成:一是较弱较窄的紫外荧光峰(346nm),另一是较强较宽的可见荧光发射峰(510nm)(λex=329nm);在反应温度为40℃,ZnAc2·2H2O与LiOH·H2O的物质摩尔比为1∶2时能产生明亮的黄绿色荧光。     

Deterministic secure quantum communication and authentication protocol based on three-particle W state and quantum one-time pad

Three-particle W states are used as decoy photons, and the eavesdropping detection rate reaches 63 %. The positions of decoy photons in information sequence are encoded with identity string ID of the legitimate users. Authentication is implemented by using previously shared identity string. State 丨φ^- ） is used as the carrier. One photon of 丨φ^-） is sent to Bob; and Bob obtains a random key by measuring photons with bases dominated by ID. The bases information is secret to others except Alice and Bob. Both the eavesdropping detection based on three-particle W state and the secret ID ensure the security of the protocol. Unitary operations are not used.     

Controlled quantum secure direct communication and authentication protocol based on five-particle cluster state and quantum one-time pad

A controlled quantum secure direct communication and authentication protocol is proposed with a quantum one-time pad based on five-particle cluster state.Photon 4 in each five-particle cluster state is sent to the controller as permission.Unitary operation I(U)on photon4 according to identity-string of the receiver is used to forbid the controller to deduce secret message.The classical XOR operation serving as a one-time-pad is used to forbid external eavesdroppers to eavesdrop.Eavesdropping detection and identity authentication are implemented by previously shared reusable base identity-strings.In one transmission,one qubit of each five-particle cluster state is used as controller’s permission,and two qubits are used to transmit two classical bit information.     

石墨相氮化碳量子点的制备与应用研究进展

近年来,世界范围内环境污染问题日益加重,能源危机也越来越凸显出来,石墨相氮化碳量子点（graphite phase carbon nitride quantum dots, g-CNQDs）作为一种非金属半导体光催化材料,因其优异的性能引起了广大研究者的关注。g-CNQDs除了用于光催化降解有机污染物和能量转换器件领域外,还凭借其良好的生物相容性、稳定的荧光发射、高量子产率和无毒性等优点在生物医学和荧光探针等领域表现出了巨大的潜能。总结了g-CNQDs的制备方法及其在光催化、能量转换、生物医学等方面的研究进展,介绍了g-CNQDs的最新研究动态,同时为其复合结构设计及性能增强提供新的研究思路。     

湿地生态系统状态参数遥感估算与分析

综合利用遥感图像处理技术和定量遥感模型,计算分析了扎龙漫地不同时期的植被指数和蒸散发量信息,研究了2001年火灾前后湿地植被生长状况的时间变化和空间差别.实验通过计算蒸腾量与植被指数的比值,来描述地面植被在不同生长阶段生长速度的差别,并利用图像变化检测技术,获取了火灾受灾区空间分布情况的相关信息.实验结果表明,在火灾中...     

Kane固体量子计算机中核自旋读出

在2个量子位(qubit)的体系中,对Kane固体量子计算机模型的通过电子状态与核子自旋状态的交换进行测量的方法进行了研究。从2个量子位系统的Hamilton量出发,根据总自旋在外磁场方向的总投影分成5个不变子空间,构造它们的块对角矩阵形式。分析了它们所有的本征值和本征态随电子之间交换相互作用的大小的变化关系。结果表明:利用核自旋和电子自旋交换来测量核自旋的方法是有一定适用范围的,在2个量子位与2个电子的系统中的16个态中,只有4个可以利用这种方法来测量。     

双模最小关联混态的纠缠及其量子起伏

研究了最小关联态的纠缠度与相关参数之间的关系。分析了不同参数情况下最小关联态发生纠缠时相关参数的取值范围以及全量子起伏与相关参数的关系;另外进一步分析了最小关联态的Wehrl熵,同时对标准EPR型纠缠态为的纠缠度作了进一步的计算。     

Preparation of multi-atom specially entangled W-class state and splitting quantum information

We give a protocol to prepare specially entangled W-class state of multi-atom which can be used to exactly teleport an arbitrarily unknown two-level two-atom state. During the process, the quantum information is split into n parts and the original quantum information can be sent to anyone of the n recipients with the other n-1 recipients＇ collaboration. In addition, we will give a suggestion to realize this scheme via QED cavity.