量子计算的研究进展

量子计算由于其强大的并行计算能力和可以有效的模拟量子行为的能力而日益受到人们的关注。本文介绍了量子计算的基本原理、实现量子计算的基本要求、量子计算的根本困难、可能的解决办法,以及当前的几个有希望实现量子计算的物理系统。最后介绍了我们课题组在分布式量子计算和基于固有耦合的编码量子计算的实验与理论方面的工作。     

固态量子计算的若干重要物理问题研究

量子计算机拥有比经典计算机更为强大的计算能力．人们普遍认为量子计算机最终将会在固态系统中实现．文章介绍了一些有关固态量子计算的研究进展，其中包括超导电荷量子比特方案、几何量子计算、量子点量子比特及量子计算若干基本问题研究．最后给出了固态量子计算的发展趋势．     

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最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。     

量子计算与量子通信

介绍了量子计算的基本原理及量子通信的可行性 ,并对量子信息的表达方式及其实现方法、量子同调态等做了探讨     

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。     

量子计算的物理实现

与经典计算相比，量子计算对信息的处理和计算有很大的优越性．在量子计算研究中，其物理实现方法的研究是一个重要部分．文章首先介绍了DiVincenzo关于量子计算的物理实现技术的7个判据，然后简要介绍了目前实现量子计算的10种物理实现方法，包括离子阱、中性原子、光学、超导约瑟夫森结、腔量子电动力学、液体核磁共振、Kane的硅基半导体方案、富勒球、量子点和液氦表面电子，基本上涵盖了目前的量子计算物理实现的进展情况．     

量子信息与计算

量子信息与计算是物理学目前研究的热门领域,本文简要地介绍量子计算的一些基本概念：量子纠缠、量子位、量子寄存器、量子并行计算和量子纠错,并介绍两种典型的量子信息技术：量子密码和量子传物。     

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.     

量子计算的进展和展望

该文主要介绍了量子计算机研究的历史和现状。强调发展大规模的量子计算和实现强关联多体系统的量子模拟,是当前量子计算研究的主流。文章主体部分主要介绍了量子计算机硬件研究方面的进展,主要聚焦于几个具有qubit可集成性的量子系统:量子点系统、超导约瑟夫森结系统、离子阱系统、腔量子电动力学系统,作为实现量子计算机的最主要的候选系统,上述方向的研究吸引了国际上研究量子计算的最主要的力量。我们调研了在这些系统中,在qubit表征、操控方面最具代表性的进展,以及在实现大规模量子计算道路上的困难,和可能的解决办法。     

量子计算的进展和展望

该文主要介绍了量子计算机研究的历史和现状.强调发展大规模的量子计算和实现强关联多体系统的量子模拟,是当前量子计算研究的主流.文章主体部分主要介绍了量子计算机硬件研究方面的进展,主要聚焦于几个具有qubit可集成性的量子系统:量子点系统、超导约瑟夫森结系统、离于阱系统、腔量子电动力学系统,作为实现量子计算机的最主要的候选系统,上述方向的研究吸引了国际上研究量子计算的最主要的力量.我们调研了在这些系统中,在qubit表征,操控方面最具代表性的进展,以及在实现大规模量子计算道路上的困难,和可能的解决办法.     

A cross-disciplinary introduction to quantum annealing-based algorithms

A central goal in quantum computing is the development of quantum hardware and quantum algorithms in order to analyse challenging scientific and engineering problems. Research in quantum computation involves contributions from both physics and computer science; hence this article presents a concise introduction to basic concepts from both fields that are used in annealing-based quantum computation, an alternative to the more familiar quantum gate model. We introduce some concepts from computer science required to define difficult computational problems and to realise the potential relevance of quantum algorithms to find novel solutions to those problems. We introduce the structure of quantum annealing-based algorithms as well as two examples of this kind of algorithms for solving instances of the max-SAT and Minimum Multicut problems. An overview of the quantum annealing systems manufactured by D-Wave Systems is also presented.     

Measurement-Based Interference in Quantum Computation

The interference has been measured by the visibility in two-level systems,which,however,does not work for multi-level systems.We generalize a measure of the interference based on decoherence process,consistent with the visibility in qubit systems.By taking cluster states as examples,we show in the one-way quantum computation that the gate fidelity is proportional to the interference of the measured qubit and is inversely proportional to the interference of all register qubits.We also find that the interference increases with the number of the computing steps.So we conjecture that the interference may be the source of the speedup of the one-way quantum computation.     

Measurement-Based Interference in Quantum Computation

The interference has been measured by the visibility in two-level systems, which, however, does not work for multi-level systems. We generalize a measure of the interference based on decoherence process, consistent with the visibility in qubit systems. By taking cluster states as examples, we show in the one-way quantum computation that the gate fidelity is proportional to the interference of the measured qubit and is inversely proportional to the interference of all register qubits. We also find that the interference increases with the number of the computing steps. So we conjecture that the interference may be the source of the speedup of the one-way quantum computation.     

从离散Wigner函数的角度探讨量子相干性度量

量子相干性是量子信息处理的基本要素,在量子计算中扮演着重要的角色.为了便于讨论量子相干性在量子计算中的作用,本文从离散Wigner函数角度对量子相干性进行了探讨.首先对奇素数维量子系统的离散Wigner函数进行了分析,分离出表征相干性的部分,提出了一种可能的基于离散Wigner函数的量子相干性度量方法,并对其进行了量子相干性度量规范的分析;同时也比较了该度量与l_1范数相干性度量之间的关系.重要的是,这种度量方法能够明确给出量子相干性程度与衡量量子态量子计算加速能力的负性和之间不等式关系,由此可以解析地解释量子相干性仅是量子计算加速的必要条件.     

Quantum simulation and quantum computation of noisy-intermediate scale

In the past years, great progresses have been made on quantum computation and quantum simulation. Increasing the number of qubits in the quantum processors is expected to be one of the main motivations in the next years, while noises in manipulation of quantum states may still be inevitable even the precision will improve. For research in this direction, it is necessary to review the available results about noisy multiqubit quantum computation and quantum simulation. The review focuses on multiqubit state generations, quantum computational advantage, and simulating physics of quantum many-body systems. Perspectives of near term noisy intermediate-quantum processors will be discussed.     

几何量子计算和拓扑量子计算——整体性量子现象的新应用

本文概述介绍量子计算的最新进展:几何量子计算和拓扑量子计算,是初步入门的引论性质。作者从量子力学的整体性现象这一观点出发,阐述作为整体现象的量子力学几何相位(亚贝尔和非亚贝尔几何相位),量子体系的拓扑不变性质等的新应用,为先前一本著作[1]所阐述观点的新发展的补充。     

Climbing Mount Scalable: Physical Resource Requirements for a Scalable Quantum Computer

The primary resource for quantum computation is Hilbert-space dimension. Whereas Hilbert space itself is an abstract construction, the number of dimensions available to a system is a physical quantity that requires physical resources. Avoiding a demand for an exponential amount of these resources places a fundamental constraint on the systems that are suitable for scalable quantum computation. To be scalable, the effective number of degrees of freedom in the computer must grow nearly linearly with the number of qubits in an equivalent qubit-based quantum computer.     

Analysis and improvement of verifiable blind quantum computation

In blind quantum computation (BQC), a client with weak quantum computation capabilities is allowed to delegate its quantum computation tasks to a server with powerful quantum computation capabilities, and the inputs, algorithms and outputs of the quantum computation are confidential to the server. Verifiability refers to the ability of the client to verify with a certain probability whether the server has executed the protocol correctly and can be realized by introducing trap qubits into the computation graph state to detect server deception. The existing verifiable universal BQC protocols are analyzed and compared in detail. The XTH protocol (proposed by Xu Q S, Tan X Q, Huang R in 2020), a recent improvement protocol of verifiable universal BQC, uses a sandglass-like graph state to further decrease resource expenditure and enhance verification capability. However, the XTH protocol has two shortcomings: limitations in the coloring scheme and a high probability of accepting an incorrect computation result. In this paper, we present an improved version of the XTH protocol, which revises the limitations of the original coloring scheme and further improves the verification ability. The analysis demonstrates that the resource expenditure is the same as for the XTH protocol, while the probability of accepting the wrong computation result is reduced from the original minimum (0.866)^d* to (0.819)^d*, where d^* is the number of repeated executions of the protocol.     

核磁共振中的量子控制

近年来, 随着量子信息科学的发展, 对由量子力学原理描述的微观世界的主动调控已成为重要的前沿研究领域. 为构造实际的量子信息处理器, 一个关键的挑战是: 如何对处于噪声环境下的量子体系实现一系列高精度的任意操作, 以完成目标量子信息处理任务. 为此, 人们将经典系统控制论的思想方法延伸到量子体系的领域, 提出了大量的量子控制方法以及相关的数值技术(如量子优化控制、量子反馈控制等), 并取得了丰富的研究成果. 核磁共振自旋体系具备成熟的系统理论和操控技术, 为量子控制方法的实用性研究提供了优秀的实验测试平台. 因此, 基于核磁共振的量子控制成为量子控制领域的重要方向. 本文简要介绍了量子控制的基本概念和方法; 从系统控制论的角度对核磁共振自旋体系的基本原理和重要控制任务做了阐述; 介绍了近些年来在该领域发展的相关控制方法及其应用; 对基于核磁共振体系的量子控制的进一步的研究做了几点展望.