有源介观电感耦合电路的本征态及热效应

研究了介观电感耦合电路中压缩态的产生及涨落压缩问题，如果电路参数电容和电感随时间变化，则有源电感耦合电路的本征态是压缩平移Fock态，当电路的频率不变时，电感增加，电荷的量子涨落有压缩，而电流的量子涨落无压缩，电感减小，电流的量子涨落有压缩，电荷的量子涨落无压缩，耦合电感有助于减小电流的量子涨落，温度上升使量子涨落增加，利用电容和电感的时间演化能够降低温度引起的热噪声。     

反铁磁拉曼散射的压缩态

在量子力学研究领域中,人们发现了许多的非经典态,压缩态是其中的一类非经典态,由不确定性关系,处于压缩态的量子涨落小于相干态的量子涨落．人们期望利用这一性质去减少量子噪声,进行高精度信号的测量．所以玻色子的压缩态研究成为物理学研究领域很重要的研究课题．该文分析了二阶拉曼散射中温度因素对量子涨落的作用,讨论了温度对磁振子压缩态的影响,确定了压缩态存在的温度范围。     

光场压缩态与纠缠态的增强及量子信息网络

光场压缩态和纠缠态是进行量子精密测量和量子信息研究的重要资源.文章简要介绍光场压缩态和纠缠态的增强及其在量子密钥分发、连续变量多组分纠缠态光场的制备、量子通信网络和量子计算中的应用.     

压缩相干态光场两耦合双原子系统的量子场熵

应用全量子理论,研究了单模压缩相干态光场和偶极与偶极力关联的两个等同的耦合双能级原子相互作用系统的量子场熵演化特性.通过数值计算,讨论了光场压缩因子、场与原子间耦合强度以及原子间耦合强度对量子场熵演化特性的影响.结果表明,光场的压缩因子影响量子场熵演化的振荡幅度;场与原子间耦合强度系数影响量子场熵演化的周期性;原子之间的耦合强度系数不仅影响量子场熵演化的振荡性,而且影响量子场熵演化的周期性.     

压缩薛定谔猫态下介观LC电路的量子效应

基于介观电容存在弱耦合特性,对介观LC电路的量子效应进行了研究.研究结果表明考虑介观电容器弱耦合效应的影响,介观LC电路将由初始的薛定谔猫态演化到压缩薛定谔猫态.并对压缩薛定谔猫态下的量子涨落进行了计算,发现压缩薛定谔猫态下磁通和电荷的量子涨落具有比薛定谔猫态下程度更高的压缩和反压缩效应.     

压缩薛定谔猫态下介观LC电路的量子效应

基于介观电容存在弱耦合特性,对介观LC电路的量子效应进行了研究.研究结果表明:考虑介观电容器弱耦合效应的影响,介观LC电路将由初始的薛定谔猫态演化到压缩薛定谔猫态.并对压缩薛定谔猫态下的量子涨落进行了计算,发现压缩薛定谔猫态下磁通和电荷的量子涨落具有比薛定谔猫态下程度更高的压缩和反压缩效应.     

基于分布式压缩感知的量子过程层析

量子过程层析是量子信息科学研究的基础之一,但其所需的实验资源会随着量子比特的增加而指数增长。考虑到过程矩阵的稀疏性,近年来一种压缩感知量子过程层析方法可以大大降低量子过程层析的成本和后处理时间。但量子通道研究需要同时层析多种量子门,并且每个量子通道在层析过程中都会存在野点数据。该文提出一种分布式压缩感知量子过程层析方法,通过组合稀疏学习的模式能同时进行多量子通道层析,并有效地剔除野点数据。仿真结果表明:相对于单通道的压缩传感量子过程层析,该方法重构的量子过程矩阵保真度高且对野点数据有较强的鲁棒性,改善了层析性能。     

量子压缩态及其熵

量子压缩态是一种新的量子态,本文利用熵的观点对其进行探讨,求得量子压缩态的存在条件,与正交相算子方法所得的结果相一致。     

强度相等的2MQES光场的奇次Y压缩特性

利用多模压缩态理论,对强度相等的两态叠加多模量子纠缠态（2MQES）光场｜ψME^（2〉q的广义非线性高次Y压缩效应进行了仔细研究。发现在满足一定的条件下,2MQES光场｜ψME^（2〉q的广义电场分量和广义磁场分量可分别呈现出广义非线性等幂次奇次Y压缩效应,且压缩规律相似,而磁场分量的压缩幅度和压缩量较大;同时指出导致2MQES光场｜ψME^（2〉q的广义电场分量和广义磁场分量存在广义非线性等幂奇次Y压缩的根原在于模间的量子干涉效应、态间的量子干涉效应以及模问和态间的量子纠缠效应。     

量子化介观RLC并联电路在压缩真空态下的量子涨落

对具有普遍意义的量子化介观RLC并联电路各支路的电流与电压在压缩真空态下的量子效应进行了研究,并对影响各支路电流与电压的量子涨落的因素进行了分析.结果表明,在压缩真空态下量子化介观RLC并联电路中各支路电流与电压的量子涨落受到电路元件的参数、压缩真空态的参数以及时间因素的影响,具体表现在各支路电流与电压的量子涨落随时间...     

利用V型三能级原子与相干态腔场的拉曼相互作用来传送三比特的未知原子态

实现量子态的隐形传送,尤其是多比特的量子态的隐形传送在量子信息领域中具有非常重要的作用。本文提出了一种用一个三原子和相干态腔场的纠缠态作为量子信道,隐形传送三比特的未知原子态的方案。     

Applying Gaussian quantum discord to quantum key distribution

In this paper, we theoretically prove that the Gaussian quantum discord state of optical field can be used to complete continuous variable （CV） quantum key distri- bution （QKD）. The calculation shows that secret key can be distilled with a Gaussian quantum discord state against entangling cloner attack. Secret key rate is increased with the increasing of quantum discord for CV QKD with the Gaussian quantum discord state. Although the calculated results point out that secret key rate using the Gaussian quantum discord state is lower than that using squeezed state and coherent state at the same energy level, we demonstrate that the Gaussian quantum discord, which only involving quantum correlation without the existence of entanglement, may provide a new resource for realizing CV QKD.     

Experimental one-way quantum computing

Standard quantum computation is based on sequences of unitary quantum logic gates that process qubits. The one-way quantum computer proposed by Raussendorf and Briegel is entirely different. It has changed our understanding of the requirements for quantum computation and more generally how we think about quantum physics. This new model requires qubits to be initialized in a highly entangled cluster state. From this point, the quantum computation proceeds by a sequence of single-qubit measurements with classical feedforward of their outcomes. Because of the essential role of measurement, a one-way quantum computer is irreversible. In the one-way quantum computer, the order and choices of measurements determine the algorithm computed. We have experimentally realized four-qubit cluster states encoded into the polarization state of four photons. We characterize the quantum state fully by implementing experimental four-qubit quantum state tomography. Using this cluster state, we demonstrate the feasibility of one-way quantum computing through a universal set of one- and two-qubit operations. Finally, our implementation of Grover's search algorithm demonstrates that one-way quantum computation is ideally suited for such tasks.     

Review on the study of entanglement in quantum computation speedup

The role the quantum entanglement plays in quantum computation speedup has been widely disputed. Some believe that quantum computation's speedup over classical computation is impossible if entan-glement is absent,while others claim that the presence of entanglement is not a necessary condition for some quantum algorithms. This paper discusses this problem systematically. Simulating quantum computation with classical resources is analyzed and entanglement in known algorithms is reviewed. It is concluded that the presence of entanglement is a necessary but not sufficient condition in the pure state or pseudo-pure state quantum computation speedup. The case with the mixed state remains open. Further work on quantum computation will benefit from the presented results.     

基于4粒子团簇态实现量子态的双向通信

提出了一个用4粒子团簇态作为量子信道传输量子态信息以实现双向通信的方案.在该方案中,通信双方Alice和Bob事先共享一个4粒子团簇态.在通信过程中:首先,将4粒子团簇态与双方要传递的量子态信息共同构成系综态;然后,Alice和Bob分别对自己拥有的部分粒子作Bell基的联合测量,并把测量结果通过经典信道告诉对方;最后,Alice和Bob根据对方公布的测量结果,作相应的幺正变换,就可以在自己的粒子上重现对方要传送的量子态信息.这样就达到了实现量子态的双向通信的目的.     

压缩真空态的激发态在介观RLC电路中的应用

在量子光学压缩真空态概念的基础上,借助玻色振子逆算符的性质,提出了压缩真空态的激发态的概念,导出了介凤ＲＬＣ电路在该量子态下电荷和电流的量子零点涨落,发现该涨落明显依赖于电路的元件,压缩参数以及激发态的量子数,并得到了该电路在绝对零点时的最子噪声。     

不同类型连续变量量子态离物传送的判据

文章利用量子力学的测量理论 ,分析了不同类型连续变量量子态在离物传送过程中的态演化 ,并推导出输出态的保真度表示式。结果表明对不同类型的输入态 ,其保真度和保真度的非经典边界有不同的形式。和相干态比较 ,当输入态为非经典量子态时 ,为达到同样的保真度必须应用具有高关联度的量子纠缠态光场     

Realization of quantum error correction

Scalable quantum computation and communication require error control to protect quantum information against unavoidable noise. Quantum error correction protects information stored in two-level quantum systems (qubits) by rectifying errors with operations conditioned on the measurement outcomes. Error-correction protocols have been implemented in nuclear magnetic resonance experiments, but the inherent limitations of this technique prevent its application to quantum information processing. Here we experimentally demonstrate quantum error correction using three beryllium atomic-ion qubits confined to a linear, multi-zone trap. An encoded one-qubit state is protected against spin-flip errors by means of a three-qubit quantum error-correcting code. A primary ion qubit is prepared in an initial state, which is then encoded into an entangled state of three physical qubits (the primary and two ancilla qubits). Errors are induced simultaneously in all qubits at various rates. The encoded state is decoded back to the primary ion one-qubit state, making error information available on the ancilla ions, which are separated from the primary ion and measured. Finally, the primary qubit state is corrected on the basis of the ancillae measurement outcome. We verify error correction by comparing the corrected final state to the uncorrected state and to the initial state. In principle, the approach enables a quantum state to be maintained by means of repeated error correction, an important step towards scalable fault-tolerant quantum computation using trapped ions.     

Tunable ion-photon entanglement in an optical cavity

Proposed quantum networks require both a quantum interface between light and matter and the coherent control of quantum states. A quantum interface can be realized by entangling the state of a single photon with the state of an atomic or solid-state quantum memory, as demonstrated in recent experiments with trapped ions, neutral atoms, atomic ensembles and nitrogen-vacancy spins. The entangling interaction couples an initial quantum memory state to two possible light-matter states, and the atomic level structure of the memory determines the available coupling paths. In previous work, the transition parameters of these paths determined the phase and amplitude of the final entangled state, unless the memory was initially prepared in a superposition state (a step that requires coherent control). Here we report fully tunable entanglement between a single (40)Ca(+) ion and the polarization state of a single photon within an optical resonator. Our method, based on a bichromatic, cavity-mediated Raman transition, allows us to select two coupling paths and adjust their relative phase and amplitude. The cavity setting enables intrinsically deterministic, high-fidelity generation of any two-qubit entangled state. This approach is applicable to a broad range of candidate systems and thus is a promising method for distributing information within quantum networks.     

柱形量子点qubit的振荡周期

通过精确求解能量本征方程获得柱型量子点中的电子能态,并利用电子的基态和第一激发态构造一个量子比特．对GaAs量子点的数值计算表明：量子点能量随半径或柱高的增大而减小;量子比特的振荡周期随半径或柱高的增大而增大．