用于规模可变量子计算网络的毫秒量子存储

量子存储可以将光的量子态存储于原子系综的自旋波激发态中,是量子中继器的关键部件。由于退相干机制的存在,使得已实现的量子存储的寿命都非常短,只有10微秒左右,这极大地限制了量子中继器在远距离量子通信中的实际应用。通常认为,短的存储寿命是由存储量子态的自旋波在梯度磁场下退相干所造成的。通过对量子存储退相干机制的详细研究,     

量子纠缠态制备、操纵的实验研究

量子纠缠是量子信息学中最重要也是最为奇特的一个课题.在量子信息学中,量子信息的处理离不开量子态及其操纵,而量子纠缠态毫无疑问是各种各样的量子态中最重要的一种. 利用光子纠缠态开展了以下实验研究:(1)利用连续波激光束泵浦非线性晶体的自发参量下转换过程,制备出了双光子偏振纠缠态,具有较高亮度和纠缠度,并具有纠缠度可调谐的特点. 利用这种纠缠源,制备了量子信息学中一种重要的混合态——Werner态,采用的方案使得Werner态中纠缠的成分是可控制的.(2)利用线性光学元件以及路径比特概念的引入,在实验上用单光子实现了Buek-Hillery普适克隆机,实验结果表明,对任意的输入纯态,此克隆机输出的2份拷贝与初始态均达到5/6的保真度,与理论计算一致.(3)在实验上利用自发参量下转换系统制备的双光子偏振最大纠缠态及非最大纠缠态进行了CHSH不等式的检验,验证了对于2比特纠缠纯态,"纠缠"等价于"Bell不等式违背"这一结论.(4)除了局域隐变量理论之外,还有一种主要的隐变量理论——环境无关的隐变量理论(NCHV),关于这种隐变量,类似于Bell不等式,有一个Kochen-Specker理论,其主要内容是证明NCHV和量子力学的矛盾. 完成了一个用单光子实现的检验Kochen-Spcker理论的实验,实验结果证明了NCHV是不存在的.     

科学家刷新冷原子量子存储纪录

中国科大潘建伟研究组与德国、奥地利的同行合作,利用对磁场不敏感的原子态来存储量子态,同时通过延长白旋波波长的实验技术,在国际上首次将单量子存储的寿命延长至毫秒量级。该实验成果将单量子存储的寿命提高了2个数量级,向未来基于量子中继器的远距离量子通信迈出了坚实的一步。研究结果发表在2月1日出版的NaturePhysics上,审稿人评价该丁作阐明并克服了一个重要的退相干机制,对光量子存储及光对物质的量子操控具有极其重要的意义。长寿命量子存储的实验实现为各种实用化的量子信息处理开创了新的起点,     

利用囚禁离子实现量子随机行走

量子随机行走具有不同于经典随机行走的性质,并且可以用来作为量子计算的算法工具。本文提出一个在离子阱中实现量子随机行走的方案,在方案中,每一步行走的操作时间都非常短,因此在消相干情况下,能增加随机行走的步数,此外,本文只采用驻波激光和脉冲激光,方案相对简单,并且在实验上是可行的。     

漫谈超导电路量子计算

受益于约瑟夫森效应的发展,超导量子比特的计算性能在过去的十年提高了几个数量级,但量子信息处理器的纠缠和多量子比特计算仍需要解决很多具体的架构问题,必须掌握量子纠错设计和系统耗散性质,使得量子纠缠能够保持。文章中在叙述现有量子计算的基础上总结了未来发展方向的蓝图。     

双暗态原子系统动力学行为的量子相干控制研究（英文）

量子相干控制前沿问题及应用研究是本世纪物理学前沿领域的重要研究内容。而基于暗态的量子相干控制技术已经导致了在相干布居捕获、绝热跟随、量子信息等多方面的应用。本论文主要进行双暗态原子系统动力学行为的若干量子相干控制研究，包括：双暗态四能级原子系统的绝热跟随特性研究；双暗态作用提高克尔非线性的新方案提出；自发辐射诱导相干实现非线性极化率的提高以及双通道高效四波混频过程的实现等。     

Kagome海森堡反铁磁体的自旋液体的基态

研究人员利用密度矩阵重正规化全来实现Kagome晶格中紧邻量子自旋S=1／2海森堡反铁磁体的基态的精确计算。该模型被用于大量圆周长达12个晶格的长柱体的研究。通过低能核小和有限尺度效应的结合．     

基于量子态相干分析的WMSN云执行信息分簇约简

无线多媒体传感网络(WMSN)云执行信息数据量大,实时性要求较高,需要对云执行信息进行分簇约简,提高WMSN的纠错能力和延长网络生命期。提出一种基于量子态相干分析的WMSN云执行信息分簇约简算法,基于量子遗传算法的WMSN网络模型,得到网络中多媒体节点的最大部署密度,采用量子态相干分析算法,进行信息数据寻优,设计WMSN云执行信息分簇策略,得到量子群移动构造的信息素约简后的空间采样分簇重构。实验得出,采用该算法,WMSN中的执行信息得到有效合理规划,分簇空间实现降秩处理,任务执行路径实现最优化模拟生成,执行同步误差较传统方法较小,从而保证了WMSN的系统稳定性和可靠性。     

动态

我国刷新最大纠缠态制备世界纪录多量子比特的操纵和纠缠是量子计算研究的核心指标。近日,我国科学家潘建伟及其同事通过调控6个光子的偏振、路径和轨道角动量3个自由度,在国际上首次实现了18个光量子比特的纠缠,刷新了所有物理体系中最大纠缠态制备的世界纪录。国际权威学术期刊《物理评论快报》日前发表了该成果。多个量子比特的相干操纵和纠缠态制备是发展可扩展量子信息技术,特别     

BP神经网络的量子学习及应用

在神经网络的训练过程当中,引入量子遗传算法,结合BP梯度下降反传训练方法构造神经网络的量子优化算法.利用量子运算的高效并行性,对神经网络实行量子编码,用量子门旋转来代替网络进化时交叉、变异等更新操作,使得网络训练收敛精度高、收敛速度快、同时避免陷入局部最优的缺点.最后提出了一种基于量子神经网络的预测方法,仿真结果表明,基于量子遗传算法的神经网络,训练次数,误差精度以及预测能力都明显优于BP神经网络.     

Rapid Lyapunov control for decoherence-free subspaces of Markovian open quantum systems

A Lyapunov-based rapid control scheme is proposed to drive a Markovian open quantum system to a decoherence-free subspace by constructing the control Hamiltonians of the system. Based on Lyapunov theory, we design a general form of control laws, which includes the standard Lyapunov control law. The convergence of the control system to the decoherence-free subspace is strictly proved. By analyzing the relationship between the LaSalle invariant set and the decoherence-free subspace, we propose a construction method for the control Hamiltonians to further speed up the control process. Simulation experiments on a three-level quantum system demonstrate that the rapid Lyapunov control scheme proposed in this paper has a good control performance.     

Experimental measurement of the quantum geometric tensor using coupled qubits in diamond

Geometry and topology are fundamental concepts, which underlie a wide range of fascinating physical phenomena such as topological states of matter and topological defects. In quantum mechanics, the geometry of quantum states is fully captured by the quantum geometric tensor. Using a qubit formed by an NV center in diamond, we perform the first experimental measurement of the complete quantum geometric tensor. Our approach builds on a strong connection between coherent Rabi oscillations upon parametric modulations and the quantum geometry of the underlying states. We then apply our method to a system of two interacting qubits, by exploiting the coupling between the NV center spin and a neighboring ¹³C nuclear spin. Our results establish coherent dynamical responses as a versatile probe for quantum geometry, and they pave the way for the detection of novel topological phenomena in solid state.     

量子计算机的发展现状与趋势

量子计算机是一种新型的运算工具,它具有强大的并行处理数据的能力,可解决现有计算机难以运算的数学问题,因此,它成为世界各国战略竞争的焦点。本文综述了量子计算机目前的发展状况和可扩展、可容错的量子计算机物理体系的实验研究进展,并分析了美国最近启动研制量子芯片的微型曼哈顿计划对我国构成的严峻挑战。     

核磁共振量子计算实验研究进展

简要评述了核磁共振量子信息处理实验研究进展。提出了我院进一步发展的建议。     

Semiconductor quantum computation

Semiconductors, a significant type of material in the information era, are becoming more and more powerful in the field of quantum information. In recent decades, semiconductor quantum computation was investigated thoroughly across the world and developed with a dramatically fast speed. The research varied from initialization, control and readout of qubits, to the architecture of fault-tolerant quantum computing. Here, we first introduce the basic ideas for quantum computing, and then discuss the developments of single- and two-qubit gate control in semiconductors. Up to now, the qubit initialization, control and readout can be realized with relatively high fidelity and a programmable two-qubit quantum processor has even been demonstrated. However, to further improve the qubit quality and scale it up, there are still some challenges to resolve such as the improvement of the readout method, material development and scalable designs. We discuss these issues and introduce the forefronts of progress. Finally, considering the positive trend of the research on semiconductor quantum devices and recent theoretical work on the applications of quantum computation, we anticipate that semiconductor quantum computation may develop fast and will have a huge impact on our lives in the near future.     

基于一次一密的量子身份识别方案

给出一个基于Holevo定理的量子单向函数,并根据它构造了一个基于对称密码体制的量子身份识别方案.该方案通过一次性的随机数隐藏了双方共享的密钥,且验证算法不依赖于所使用的随机数,从而保护了密钥,使该方案的安全性不局限于敌手的计算能力.     

Electric field manipulation enhanced by strong spin-orbit coupling: promoting rare-earth ions as qubits

Quantum information processing based on magnetic ions has potential for applications as the ions can be modified in their electronic properties and assembled by a variety of chemical methods. For these systems to achieve individual spin addressability and high energy efficiency, we exploited the electric field as a tool to manipulate the quantum behaviours of the rare-earth ion which has strong spin-orbit coupling. A Ce:YAG single crystal was employed with considerations to the dynamics and the symmetry requirements. The Stark effect of the Ce³⁺ ion was observed and measured. When demonstrated as a quantum phase gate, the electric field manipulation exhibited high efficiency which allowed up to 57 π/2 operations before decoherence with optimized field direction. It was also utilized to carry out quantum bang-bang control, as a method of dynamic decoupling, and the refined Deutsch-Jozsa algorithm. Our experiments highlighted rare-earth ions as potentially applicable qubits because they offer enhanced spin-electric coupling which enables high-efficiency quantum manipulation.     

量子计算的语形表征及其意义

量子计算研究是近年来量子力学最具潜力的发展方向之一。文章从探讨量子计算概念的提出入手,讨论了经典可逆计算的量子表征模式,接着分析了量子计算语形结构的特点,对比了量子计算与经典计算并行性的异同,考虑了测量中的塌缩对量子算法设计的影响,最后以前述的研究为基础讨论了量子计算的哲学意义。     

On the dynamics of a quantum coherent feedback network of cavity-mediated double quantum dot qubits

The purpose of this paper is to present a comprehensive study of a coherent feedback network where the main component consists of two distant double quantum dot (DQD) qubits which are directly coupled to a cavity. This main component has recently been physically realized (van Woerkom et al., Microwave photon-mediated interactions between semiconductor qubits, Physical Review X, 8(4):041018, 2018). The feedback loop is closed by cascading this main component with a beamsplitter. The dynamics of this coherent feedback network is studied from three perspectives. First, an analytic form of the output single-photon state of the network driven by a single-photon state is derived. In contrast to the experimental observations made in the above paper where a laser is used as input, new interesting physical phenomena are revealed by means of single-photon input. Second, excitation probabilities of DQD qubits are computed when the network is driven by a single-photon input state. Finally, if the input is vacuum but one of the two DQD qubits is initialized in its excited state, the explicit expression of the steady-state joint system-field state is derived, which shows that the output single-photon field and the two DQD qubits can form an entangled state if the transition frequencies of two DQD qubits are equal. This analytical expression can be used to interpret experimental results in the existing literature.