边界交流关系、量子系统消耗与量子组织均衡

本文探讨建立以环境提供的熵流为自变量的熵变函数;当熵变化取负值时,此函数可称 作有序生成函数。在此基础上,从量子系统为形成并维持有序化的低熵态而由环境提供可转化为物质的能量流或熵流方面考虑量子系统的消耗,建立量子消耗函数;从量子系统经过非平衡相变而由无序化的高熵态转入有序化的低熵态方面考虑量子系统的补偿,建立量子补偿函数;进而在量子消耗和量子补偿之间取剩余,形成量子组织增益量。量子系统总是在一定的消耗下力图达到最大的组织增益,可将这一目标状态看作量子组织均衡（或量子组织平衡）。     

Quantum Discord in Two-Qubit System Constructed from the Yang–Baxter Equation

Quantum correlations among parts of a composite quantum system are a fundamental resource for several applications in quantum information. In general, quantum discord can measure quantum correlations. In that way, we investigate the quantum discord of the two-qubit system constructed from the Yang-Baxter Equation. The density matrix of this system is generated through the unitary Yang-Baxter matrix R. The analytical expression and numerical result of quantum discord and geometric measure of quantum discord are obtained for the Yang-Baxter system. These results show that quantum discord and geometric measure of quantum discord are only connect with the parameter θ, which is the important spectral parameter in Yang Baxter equation.     

Steering quantum nonlocalities of quantum dot system suffering from decoherence

The important applications of quantum dot system are to implement logic operations and achieve universal quantum computing based on different quantum nonlocalities. Here, we characterize the quantum steering, Bell nonlocality, and nonlocal advantage of quantum coherence (NAQC) of quantum dot system suffering nonunital and unital channels. The results reveal that quantum steering, Bell nonlocality, and NAQC can display the traits of dissipation, enhancement, and freezing. One can achieve the detections of quantum steering, Bell nonlocality, and NAQC of quantum dot system in different situations. Among these quantum nonlocalities, NAQC is the most fragile, and it is most easily influenced by different system parameters. Furthermore, considering quantum dot system coupling with amplitude damping channel and phase damping channel, these quantum nonlocalities degenerate with the enlargement of the channel parameters $t$ and $\varGamma$. Remarkably, measurement reversal can effectively control and enhance quantum steering, Bell nonlocality, and NAQC of quantum dot system suffering from decoherence, especially in the scenarios of the amplitude damping channel and strong operation strength.     

量子计算与量子模拟

量子计算和量子模拟在过去的几年里发展迅速,今后涉及多量子比特的量子计算和量子模拟将是一个发展的重点.本文回顾了该领域的主要进展,包括量子多体模拟、量子计算、量子计算模拟器、量子计算云平台、量子软件等内容,其中量子多体模拟又涵盖量子多体动力学、时间晶体及多体局域化、量子统计和量子化学等的模拟.这些研究方向的回顾是基于对现阶段量子计算和量子模拟研究特点的考虑,即量子比特数处于中等规模而量子操控精度还不具有大规模逻辑门实现的能力,研究处于基础科研和实用化的过渡阶段,因此综述的内容主要还是希望管窥今后的发展.     

光子两自由度超并行量子计算与超纠缠态操控

光子系统在量子信息处理和传输过程中有非常重要的应用. 譬如, 利用光子与原子(或人工原子)之间的相互作用, 可以完成信息的安全传输、存储和快速的并行计算处理等任务. 光子系统具有多个自由度, 如极化、空间模式、轨道角动量、时间-能量、频率等自由度. 光子系统的多个自由度可以同时应用于量子信息处理过程. 超并行量子计算利用光子系统多个自由度的光量子态同时进行量子并行计算, 使量子计算具有更强的并行性, 且需要的量子资源少, 更能抵抗光子数损耗等噪声的影响. 多个自由度同时存在纠缠的光子系统量子态称为超纠缠态, 它能够提高量子通信的容量与安全性, 辅助完成一些重要的量子通信任务. 在本综述中, 我们简要介绍了光子系统两自由度量子态在量子信息中的一些新应用, 包括超并行量子计算、超纠缠态分析、超纠缠浓缩和纯化三个部分.     

Quantum coherence,evolution of the Wigner function,and transition from quantum to classical dynamics for a chaotic system

The paper deals with dynamics of a quantum chaotic system under influence of an environment. The effect of an environment is known to destroy the quantum coherence and can convert the quantum dynamics of a system to classical. We use a semiclassical technique for studying the process of decoherence. The condition for transition from quantum to classical dynamics is obtained in general form and checked numerically for a particular chaotic system, known as quantum the standard map on a torus. The relevance of the obtained results to the problem of correspondence between quantum and classical mechanics is briefly discussed. (c) 1996 American Institute of Physics.     

失谐量子频率转换系统薛定谔方程的显式解析解

根据光和频产生过程的动力学演化总是保持闲置光和信号光的光子数之和守恒这一性质,构建出了光学谐振腔中频率转换系统的含时不变量.并运用此不变量及Lewis-Riesenfeld量子不变量方法,在失谐情形下,对这一双模量子化电磁场耦合系统相应的薛定谔方程进行了求解.得到了系统随时间演化的量子态和演化算符的显示解析表达式.此解对于进一步研究系统各种量子性质是有用的.     

A prototype of quantum von Neumann architecture

A modern computer system, based on the von Neumann architecture, is a complicated system with several interactive modular parts. It requires a thorough understanding of the physics of information storage, processing, protection, readout, etc. Quantum computing, as the most generic usage of quantum information, follows a hybrid architecture so far, namely, quantum algorithms are stored and controlled classically, and mainly the executions of them are quantum, leading to the so-called quantum processing units. Such a quantum–classical hybrid is constrained by its classical ingredients, and cannot reveal the computational power of a fully quantum computer system as conceived from the beginning of the field. Recently, the nature of quantum information has been further recognized, such as the no-programming and no-control theorems, and the unifying understandings of quantum algorithms and computing models. As a result, in this work, we propose a model of a universal quantum computer system, the quantum version of the von Neumann architecture. It uses ebits (i.e. Bell states) as elements of the quantum memory unit, and qubits as elements of the quantum control unit and processing unit. As a digital quantum system, its global configurations can be viewed as tensor-network states. Its universality is proved by the capability to execute quantum algorithms based on a program composition scheme via a universal quantum gate teleportation. It is also protected by the uncertainty principle, the fundamental law of quantum information, making it quantum-secure and distinct from the classical case. In particular, we introduce a few variants of quantum circuits, including the tailed, nested, and topological ones, to characterize the roles of quantum memory and control, which could also be of independent interest in other contexts. In all, our primary study demonstrates the manifold power of quantum information and paves the way for the creation of quantum computer systems in the near future.     

约化密度矩阵及其在量子信息处理中的应用

密度矩阵在量子力学中主要是扩展了态矢量的概念.约化密度矩阵是通过对整个系统中的密度矩阵的某一子系求部分迹得到的.本文首先介绍了约化密度矩阵的定义,然后指出约化密度矩阵在纠缠态的定义、两体系统中量子纠缠的度量、系统与环境耦合造成的退相干的物理机制等量子信息前沿领域方面的应用.     

Entropic Uncertainty in Neutrino and Meson Systems

The dynamics of quantum‐memory‐assisted entropic uncertainty for the closed neutrino system in the context of two flavor oscillations and the meson system within the framework of open quantum system are investigated. It is found that the entropic uncertainty exists in close relation with the quantum correlation, and growing quantum correlation can decrease the uncertainty. The oscillatory behaviors of entropic uncertainty in neutrino system brought about by neutrino oscillating property are different from the decaying behaviors of entropic uncertainty in meson system induced by the meson decaying nature. In addition, the entropic uncertainty is always equal to its lower bound in the two subatomic systems. This study would throw light on the particle behavior characteristics of high energy physics, and may be useful to the tasks of quantum information‐processing implemented with subatomic system since the uncertainty principle plays vital role in quantum information science and technology.     

Thermal quantum correlations of a spin-1/2 Ising-Heisenberg diamond chain with Dzyaloshinskii-Moriya interaction

We investigate the properties of thermal quantum correlations in an infinite spin-1/2 Ising-Heisenberg diamond chain with Dzyaloshinskii-Moriya(DM) interaction. The thermal quantum discord(TQD) and the thermal entanglement(TE)are discussed as two kinds of important methods to measure the quantum correlation, respectively. It is found that DM interaction plays an important role in the thermal quantum correlations of the system. It can enhance the thermal quantum correlations by increasing DM interaction. Furthermore, the thermal quantum correlations can be promoted by tuning the external magnetic field and the Heisenberg coupling parameter in the antiferromagnetic system. It is shown that the behaviors of TQD differ from those of TE. TQD is more robust against decoherence than TE. For the measurement of TQD, the "regrowth" phenomenon occurs in the ferromagnetic system. We also find that the anisotropy favors the thermal quantum correlations of the system with weak DM interaction.     

The Measurement Process in the Generalized Contexts Formalism for Quantum Histories

In the interpretations of quantum mechanics involving quantum histories there is no collapse postulate and the measurement is considered as a quantum interaction between the measured system and the measured instrument. For two consecutive non ideal measurements on the same system, we prove that both pointer indications at the end of each measurement are compatible properties in our generalized context formalism for quantum histories. Inmediately after the first measurement an effective state for the measured system is deduced from the formalism, generalizing the state that would be obtained by applying the state collapse postulate.     

Quantum decoherence in the theory of open systems

Within the framework of the Lindblad theory for open quantum systems, we determine the degree of quantum decoherence of a harmonic oscillator interacting with a thermal bath. It is found that the system manifests a quantum decoherence which is more and more significant in time. We also calculate the decoherence time scale and analyze the transition from quantum to classical behavior of the considered system. The text was submitted by the author in English.     

Kerr相互作用下量子相干性分布和量子信息流动

本文针对Kerr相互作用下系统中量子相干性的动力学分布进行了研究.所讨论系统包含两个没有相互作用的原子,每个原子都被囚禁在各自的光腔中,同时光腔被充满了非线性Kerr介质.研究发现非线性Kerr相互作用能够增加两原子间的量子相干性,而且增大的幅度会随着Kerr相互作用强度的增加而得以提高.其次,借助迹距离的方法,还探讨了非线性Kerr相互作用对于原子与光腔之间的量子信息流动的影响,发现Kerr相互作用可以加快量子信息回流到原子子系统中,抑制原子子系统与其余子系统间的量子信息交换,阻碍量子信息在系统中不同子系统间的流动,从而保护原子子系统中拥有的量子信息.     

Quantum Information Transfer from a Double Quantum Dot System to a Cavity Field＊

In this paper, we propose a scheme to realize quantum information transfer from a double quantum dot （DQD） system to a quantized cavity field. The DQD and the cavity field are treated as a two-state charge qubit and a continuous-variable system, respectively. It is shown that quantum information encoded in the two-state DQD system can be transferred to quantum states of the cavity field with a continuous-variable basis through appropriate projective measurements with respect to the DQD.     

二维形变谐振子系统中的量子经典对应

通过引入等效普朗克常数,将量子系统中基本动力学变量的期望值和经典系统中基本动力学变量的精确值的时间演化行为相比较,分析了两者产生差异的因素,规则运动主要是和量子效应有关,而混沌运动则是和动力学效应有关,即与系统的动力学对称性破坏相联系.在此基础上,比较了量子相空间测不准度和李雅谱诺夫指数,给出了令人满意的说明.     

Inhibition of Atomic Decay in Strongly Coupled Photonic Crystal Cavities

We discuss the evolution dynamics of a quantum system consisting of two two-level atoms separately embedded within two strongly coupled photonic crystal cavities.Although the quantum system is subjected to dissipation and decoherence from the cavity leakage and the atomic decay,it does allow for eigenstates that are not influenced by one of the two dissipation channels and results in dissipation-inhibition quantum states.These dissipationfree quantum states can help to achieve an extremely long photon and atom storage lifetime and provide a new perspective to realize efficient quantum information storage via reducing the negative influence of the dissipation from the environment.     

General Quantum Interference Principle and Duality Computer

In this article, we propose a general principle of quantum interference for quantum system, and based on this we propose a new type of computing machine, the duality computer, that may outperform in principle both classical computer and the quantum computer. According to the general principle of quantum interference, the very essence of quantum interference is the interference of the sub-waves of the quantum system itself. A quantum system considered here can be any quantum system: a single microscopic particle, a composite quantum system such as an atom or a molecule, or a loose collection of a few quantum objects such as two independent photons. In the duality computer, the wave of the duality computer is split into several sub-waves and they pass through different routes, where different computing gate operations are performed. These sub-waves are then re-combined to interfere to give the computational results. The quantum computer, however, has only used the particle nature of quantum object. In a duality computer, it may be possible to find a marked item from an unsorted database using only a single query, and all NP-complete problems may have polynomial algorithms. Two proof-of-the-principle designs of the duality computer are presented: the giant molecule scheme and the nonlinear quantum optics scheme. We also propose thought experiment to check the related fundamental issues, the measurement efficiency of a partial wave function.     

Enhancing the capability of controlling quantum systems via ancillary systems

This paper explores the potential of controlling quantum systems by introducing ancillary systems and then performing unitary operation on the resulting composite systems. It generalizes the concept of pure state controllability for quantum systems and establishes the link between the operator controllability of the composite system and the generalized pure state controllability of its subsystem. It is constructively demonstrated that if a composite quantum system can be transferred between any pair of orthonormal pure vectors, then its subsystem is generalized pure-state controllable. Furthermore, the unitary operation and the coherent control can be concretely given to transfer the system from an initial state to the target state. Therefore, these properties may be potentially applied in quantum information, such as manipulating multiple quantum bits and creating entangled pure states. A concrete example has been given to illustrate that a maximally entangled pure state of a quantum system can be generated by introducing an ancillary system and performing open-loop coherent control on the resulting composite system.