Spin-Based Quantum Information Processing in Magnetic Quantum Dots

We define the qubit as a pair of singlet and triplet states of two electrons in a He-type quantum dot (QD) placed in a diluted magnetic semiconductor (DMS) medium. The molecular field is here essential as it removes the degeneracy of the triplet state and strongly enhances the Zeeman splitting. Methods of qubit rotation as well as two-qubit operations are suggested. The system of a QD in a DMS is described in a way which allows an analysis of the decoherence due to spin waves in the DMS subsystem.on leave from Institute of Physics, Odessa UniversityPresented at the 36th Symposium on Mathematical Physics, “Open Systems & Quantum Information”, Toruń, Poland, June 9–12, 2004.     

量子密码通信的信号发送与处理系统

自行研制了一套用于量子密码通信的信号发送与处理系统,该系统将自制的半导体激光器驱动电路、相位调制器驱动电路、单光子探测器电路、数据处理及计算机通讯等电路连接起来,与相应光纤光路一起构成了我国第一个光纤量子密码通信系统。     

Quantum Information Processing in Cavity-QED

We give a brief overview of cavity-QED and its roles in quantum information science. In particular, we discuss setups in optical cavity-QED, where either atoms serve as stationary qubits, or photons serve as flying qubits. PACS: 42.50.Pq, 03.67.Lx, 03.67.Hk, 32.80.Pj     

一种可验证的量子匿名通信方案

提出一种新的消息发送者和接收者同时匿名的经典消息通信方案.方案通过制备量子连续变量纠缠态,在参与者中移动式传输粒子,将1比特经典消息编码在不同的模式中.消息接收者可以计算得到匿名消息,然后通过不同模式的计算结果检验本次通信中的参与者诚实度,从而判断匿名消息是否有效.方案将传输和检测两个过程合并设计在同一轮通信中,通信信号和检测结论基于同一轮通信中的信道编码,可以验证具有自适应特征的参与者(检测过程和通信过程表现不一致的参与者)作弊.除了指数小的概率,发送者和接收者的匿名性和消息的私密性都得到保护.     

异构家庭网络中融合量子信息技术的安全通信协议

随着量子信息技术与家庭网络技术日益紧密结合,采用量子密钥确保家庭网络的通信安全已经成为大势所趋.针对目前数字家庭通信网络的安全日益复杂和多样化的问题,提出了异构家庭网络中融合量子信息技术的安全通信协议,智能终端设备、家庭网关、业务管理平台内的服务器共享量子GHZ 态,根据GHZ 三重态的内在特性,从而实现业务管理平台内的服务器对智能终端设备的合法性访问和数据处理.该协议利用现有手段可以实现.     

基于量子Calderbank-Shor-Steane纠错码的量子安全直接通信

量子安全直接通信是继量子密钥分配之后提出的又一重要量子密码协议,它要求通信双方在预先不需要建立共享密钥的情况下就可以实现消息的保密传输.给出了一个新的量子安全直接通信方案,该方案利用量子Calderbank-Shor-Steane(CSS)纠错码和未知量子态不可克隆等性质,方案的安全性建立在求解一般的线性码的译码问题是一个NP完全问题、Goppa码有快速的译码算法和量子图灵机不能有效求解NP完全问题的基础上.在协议中,发送方Alice把要发送的秘密消息转化为一一对应的错误向量,把错误向量加到其接收到的、Bob编码过的量子态上,并发给接收方Bob.Bob利用其私钥,通过测量、解码可以得到错误向量,并可以用相应的算法恢复出秘密消息.控制量子信道的攻击者Eve不能恢复出秘密消息,因其不知道Bob的密钥.与已有的量子安全直接通信方案相比,该方案不需要交换任何额外的经典信息和建立量子纠缠信道.     

Quantum Information Processing with Trapped Neutral Atoms

Quantum information can be processed using large ensembles of ultracold and trapped neutral atoms, building naturally on the techniques developed for high-precision spectroscopy and metrology. This article reviews some of the most important protocols for universal quantum logic with trapped neutrals, as well as the history and state-of-the-art of experimental work to implement these in the laboratory. Some general observations are made concerning the different strategies for qubit encoding, transport and interaction, including trade-offs between decoherence rates and the likelihood of two-qubit gate errors. These trade-offs must be addressed through further refinements of logic protocols and trapping technologies before one can undertake the design of a general-purpose neutral-atom quantum processor. PACS: 03.67.Lx, 32.80.Pj, 34.50.-s     

Some Issues in Quantum Information Theory

Quantum information theory is a new interdisciplinary research field related to quantum mechanics, computer science, information theory, and applied mathematics. It provides completely new paradigms to do information processing tasks by employing the principles of quantum mechanics. In this review, we first survey some of the significant advances in quantum information theory in the last twenty years. We then focus mainly on two special subjects： discrimination of quantum objects and transformations between entanglements. More specifically, we first discuss discrimination of quantum states and quantum apparatus in both global and local settings. Secondly, we present systematical characterizations and equivalence relations of several interesting entanglement transformation phenomena, namely entanglement catalysis, multiple-copy entanglement transformation, and partial entanglement recovery.     

Implementing a Quantum Algorithm with Exchange-Coupled Quantum Dots: A Feasibility Study

We present Monte Carlo wavefunction simulations for quantum computations employing an exchange-coupled array of quantum dots. Employing a combination of experimentally and theoretically available parameters, we find that gate fidelities greater than 98% may be obtained with current experimental and technological capabilities. Application to an encoded 3 qubit (nine physical qubits) Deutsch-Josza computation indicates that the algorithmic fidelity is more a question of the total time to implement the gates than of the physical complexity of those gates. PACS: 81.07.Ta, 02.70.Ss, 03.67.Lx, 03.65.Yz     

量子计算与量子计算机

量子计算的强大运算能力使得量子计算机具有广阔的应用前景。该文简要介绍了量子计算的发展现状和基本原理,列举了典型的量子算法,阐明了量子计算机的优越性,最后预测了量子计算及量子计算机的应用方向。     

基于近红外荧光量子点的防伪技术基础研究

提出了一种新型的利用近红外荧光量子点作为载体的防伪方法,并进行了相关基础研究,应对了产品市场对防伪技术不断革新的需要;设计了微弱荧光光谱测试系统,系统研究了双波长荧光量子点防伪识别技术,得出双波长荧光光谱识别的基本方法,将近红外荧光量子点的荧光强度之间的差异作为识别的依据,设计出相应的编码方法即可以对信息进行加密;测试结果表明该方法切实可行;研究结果对近红外荧光量子点的防伪识别有重要的指导意义,为防伪技术打开了更广阔的发展空间。     

Fiber Optics Protocols for Quantum Communication

We show how the techniques developed for long distance quantum key distribution in optical fibers can be used to demonstrate other quantum information processing and communication protocols. We present a fiber optics realization of the Deutsch–Jozsa and Bernstein–Vazirani algorithms. We describe a method, called “error filtration”, for reducing errors in quantum communication channels, and present an experimental implementation thereof. We discuss the cryptographic primitive of string flipping, and present an experimental implementation which has higher security than achievable using any classical protocol.     

Quantum Computing and Information Extraction for Dynamical Quantum Systems

We discuss the simulation of complex dynamical systems on a quantum computer. We show that a quantum computer can be used to efficiently extract relevant physical information. It is possible to simulate the dynamical localization of classical chaos and extract the localization length with quadratic speed up with respect to any known classical computation. We can also compute with algebraic speed up the diffusion coefficient and the diffusion exponent, both in the regimes of Brownian and anomalous diffusion. Finally, we show that it is possible to extract the fidelity of the quantum motion, which measures the stability of the system under perturbations, with exponential speed up. The so-called quantum sawtooth map model is used as a test bench to illustrate these results. PACS: 03.67.Lx, 05.45.Mt     

“乒乓”量子通信协议的不安全性

"乒乓"量子通信协议的量子直接通信已引起了许多学者们的关注,然而,由于双向量子信道的对称性,该协议存在安全性缺陷.基于量子纠错码(QECC)编码原理和构造技术提出了一种新的攻击策略.基于该攻击策略分别对纠缠态和非正交态的"乒乓"协议进行了论证,并从信息论角度对Eve可以获得的信息量和可能被检测到的概率进行了分析.分析结果表明,以前提出的"乒乓"量子通信协议都是不安全的,即攻击者可以在不被检测到的情况下获得传输的信息.     

Controlling Spin Qubits in Quantum Dots

We review progress on the spintronics proposal for quantum computing where the quantum bits (qubits) are implemented with electron spins. We calculate the exchange interaction of coupled quantum dots and present experiments, where the exchange coupling is measured via transport. Then, experiments on single spins on dots are described, where long spin relaxation times, on the order of a millisecond, are observed. We consider spin-orbit interaction as sources of spin decoherence and find theoretically that also long decoherence times are expected. Further, we describe the concept of spin filtering using quantum dots and show data of successful experiments. We also show an implementation of a read out scheme for spin qubits and define how qubits can be measured with high precision. Then, we propose new experiments, where the spin decoherence time and the Rabi oscillations of single electrons can be measured via charge transport through quantum dots. Finally, all these achievements have promising applications both in conventional and quantum information processing. PACS: 03.67.Lx, 03.67.Mn, 73.23.Hk, 85.35.Be     

The Data Compression Theorem for Ergodic Quantum Information Sources

We extend the data compression theorem to the case of ergodic quantum information sources. Moreover, we provide an asymptotically optimal compression scheme which is based on the concept of high probability subspaces. The rate of this compression scheme is equal to the von Neumann entropy rate.PACS:03.67-a; 02.50.Ey; 89.70.+c.     

量子假设检验互信息

von Neumann互信息是Shannon互信息在量子信息中的推广,在量子信道容量中有非常好的应用.由于量子态的非对易性,许多经典信息论中的量化在量子信息中有完全不等价的推广定义.量子假设检验相对熵来自于假设检验问题,是量子信息处理中常用的基本量化之一.使用量子假设检验相对熵讨论量子互信息. 首先讨论量子假设检验相对熵的一些基本性质,并给出该量化和其他量子广义熵之间的关系. 然后结合相对熵的性质,给出量子假设检验互信息的定义,并讨论其性质,比如：数据处理不等式.通过互信息与条件熵之和重点讨论互信息的链式法则.