基于量子层析的量子态测量方案及其仿真

为解决量子态信息获取问题,基于量子层析理论,深入分析了单量子比特和多量子比特的层析理论,设计了利用量子态层析进行量子态测量的实验方案,并通过计算机仿真技术对单量子比特层析实验进行了模拟．在理论分析和仿真实验的基础上得到如下结论：通过适当选取测量次数,量子层析技术可以较为精确地重构量子态密度矩阵,获取量子态信息,同时可以兼顾实验效率．

     

基于单量子态的量子加密协议

由于量子的特殊性,量子加密的实现存在许多困难,因此量子密码学中量子加密协议很少。该文分析了实现量子加密的几个障碍:量子态的不确定性、量子比特传输的噪声和错误等,并且就克服这些障碍提出了量子密码的新分支-基于单量子态的量子加密协议。该量子加密协议利用传统密码学、纠错编码和量子力学原理相结合实现保密信息传递,同时分析了量子加密协议的安全性和其他特点。     

量子态估计简介及其在超导电路电动力学系统中的应用

量子态估计是量子计算以及量子调控的基础,一般分为量子态层析,即对未知量子态(或过程的初态)进行估计,以及量子滤波,即对量子态进行实时的估计.本文首先介绍了近年来量子态层析技术新的进展,内容包括极大似然方法,压缩感知方法和线性回归方法,并分析了它们的适用范围及各自的优缺点.进一步,基于量子计算的成熟载体超导电路电动力学系统,介绍了基于连续弱测量对量子态进行实时估计的贝叶斯方法,并分析了贝叶斯估计的适用情形.进一步,通过仿真实现了量子贝叶斯估计,可以很容易发现贝叶斯方法能够精确地实时追踪量子态的演化.     

单量子比特系统状态的在线估计

针对具有退相干效应与测量反馈随机噪声的随机开放量子系统, 采用对状态影响较弱的连续弱测量在线获取一系列状态的部分信息, 实现量子状态的在线估计.由泡利矩阵构造初始测量算符, 并推导出在线的随时间变化的测量算符; 基于压缩传感理论来减少测量次数; 采用最小二乘优化算法对自由演化中的量子密度矩阵状态进行重构, 完整地给出了量子态在线估计的过程.所提出的在线量子态估计方案, 在一个量子位系统上进行了系统仿真实验.数值仿真实验结果表明, 在满足压缩传感理论的条件下, 仅需2次连续弱测量所得到的测量值之后, 就可以高精度地实现在线变化的单比特量子密度矩阵估计.     

无信息泄露的四粒子的量子安全会话

量子信息学是近年来由量子力学与信息科学相结合而产物的一门新兴的学科,量子通信是其重要的分支。量子通信将量子力学定律引入传统通信中,其安全性由量子力学的基本原理所保证,如未知量子位不可克隆、非正交量子态不可识别、量子态测量无法不扰动系统状态等,可以实现绝对安全的通信。本文基于二粒子无信息泄露的量子安全会话,在阅读大量文献的基础上,提出了一种一次传输8比特秘密信息的思想。结合已有方案,列出的一种利用四粒子纠缠交换实现的无信息泄露的量子安全会话方案。     

在噪声情况下远程制备四比特团簇态

本文采用团簇态作为量子信道,讨论了4种噪声对远程制备四比特团簇态的影响.首先分析在理想情况下,制备者Alice利用团簇态作为量子信道,通过构造巧妙的测量基,帮助接收者Bob获取所需制备的目标四比特团簇态;然后讨论在4种噪声影响下远程制备四比特团簇态,且利用保真度来描述输出态与输入态之间的接近程度.发现不同类型的噪声对远程量子态制备的影响程度不同.尤其相位噪声,在远程量子制备四比特团簇态的过程中,系统的保真度不受待制备量子态的相位因素的影响,然而其他3种噪声都受待制备量子态的相位因素的影响.     

基于对称W态和身份认证的安全量子通信协议

由于W态纠缠的强鲁棒性,它被认为是更适用于量子信息处理和量子安全通信的信息载体。针对4粒子W态或3粒子非对称W态量子直接通信效率低下或物理实现困难等缺陷,利用3粒子对称W态和量子身份认证机制,提出了一种新的确定型安全量子通信协议。该协议由认证码生成、量子态准备、量子态分发、安全检测与身份认证和消息通信五阶段组成,通信双方只需进行两粒子Bell基、单粒子Z基或X基测量,通信效率也有所提高,即1个3粒子W态传输1经典比特信息。安全分析证明该协议能有效抵抗各类窃听者Eve攻击和伪装攻击,具有较好的安全特性。     

基于对称W态和身份认证的安全量子通信协议

由于W态纠缠的强鲁棒性,它被认为是更适用于量子信息处理和量子安全通信的信息载体。针对4粒子W态或3粒子非对称W态量子直接通信效率低下或物理实现困难等缺陷,利用3粒子对称W态和量子身份认证机制,提出了一种新的确定型安全量子通信协议。该协议由认证码生成、量子态准备、量子态分发、安全检测与身份认证和消息通信五阶段组成,通信双方只需进行两粒子Bell基、单粒子Z基或X基测量,通信效率也有所提高,即1个3粒子W态传输1经典比特信息。安全分析证明该协议能有效抵抗各类窃听者Eve攻击和伪装攻击,具有较好的安全特性。     

两能级封闭量子系统任意量子态的最优制备

在分析单量子位的Bloch球面表示的基础上,结合量子门实现量子态幺正演化的量子态调控机制,提出一种针对两能级封闭量子系统任意量子态的最优制备策略．该策略首先建立两能级量子系统及其控制场的模型;然后借助李群李代数．由经典最优控制的思想和约化动力学来获得最优控制,从而达到两能级封闭量子系统任意量子态的最优制备．理论分析与仿真实验表明了该策略的优越性．     

基于量子委托计算模式的半量子密钥协商

为降低量子设备的成本,更好地执行量子计算,提出基于量子委托计算模式的多方半量子密钥协商协议。引入量子委托计算模式,将酉操作、Bell测量等复杂量子操作委托到量子中心进行,而参与者仅需具备访问量子信道与制备单光子的简单能力。为防止密钥信息被量子中心以及外部窃听者窃取,采用在目标量子态中插入混淆单光子的混淆策略来保证目标量子态的隐私性。分析结果表明,与其他量子密钥协商协议相比,参与者所需的量子能力显著降低,从而提升了协议的实际可行性。     

Joint remote control of an arbitrary single-qubit state by using a multiparticle entangled state as the quantum channel

We present a scheme for joint remote implementation of an arbitrary single-qubit operation following some ideas in one-way quantum computation. All the senders share the information of implemented quantum operation and perform corresponding single-qubit measurements according to their information of implemented operation. An arbitrary single-qubit operation can be implemented upon the remote receiver’s quantum system if the receiver cooperates with all the senders. Moreover, we study the protocol of multiparty joint remote implementation of an arbitrary single-qubit operation with many senders by using a multiparticle entangled state as the quantum channel.     

Quantum broadcast scheme and multi-output quantum teleportation via four-qubit cluster state

In this paper, two theoretical schemes of the arbitrary single-qubit states via four-qubit cluster state are proposed. One is three-party quantum broadcast scheme, which realizes the broadcast among three participants. The other is multi-output quantum teleportation. Both allow two distant receivers to simultaneously and deterministically obtain the arbitrary single-qubit states, respectively. Compared with former schemes of an arbitrary single-qubit state, the proposed schemes realize quantum multi-cast communication efficiently, which enables Bob and Charlie to obtain the states simultaneously in the case of just knowing Alice’s measurement results. The proposed schemes play an important role in quantum information, specially in secret sharing and quantum teleportation.     

Grover量子搜索算法的仿真实现

利用核磁共振(NMR)实验技术来实现量子计算,是当前各种验证量子算法最为有效的方法之一,但这个方法首先必须把量子算法编译成在现代超导核磁共振谱仪上能够直接执行的NMR脉冲序列,即NMR量子计算程序。在NMR技术中通常只要施加合适的射频脉冲,便可以达到使核自旋翻转以实现某种逻辑功能的目的,该文讨论了如何设计多量子位核磁共振(NMR)脉冲序列来实现Grower量子搜索算法,并在量子仿真器(QCE)上进行了实验验证。     

以最大slice态为信道的受控量子远程控制

利用三量子最大slice态作为量子信道,提出了单量子酉算子的受控远程执行的两个协议.首先,利用双向量子隐形传态(BQST),给出了一个任意单量子酉算子的受控隐形传输方案.结果 表明,通过非最大纠缠信道,发送者能够在遥远的接受者的量子系统上远程地执行一个任意单量子酉算子.如果发送者和控制者对各自量子执行恰当的投影测量,那...     

Quantum Universality from Magic States Distillation Applied to CSS Codes

Given Clifford group operations and the ability to repeatedly prepare a single-qubit mixed state ρ, can one do universal quantum computation? We show a sharp threshold in the Hadamard “magic” direction of the Bloch sphere between those ρ allowing universal quantum computation, and those for which any calculation can be efficiently classically simulated. As a corollary, the ability to repeatedly prepare any pure state which is not a stabilizer state (e.g., any single-qubit pure state which is not a Pauli eigenstate), together with Clifford group operations, gives quantum universality. As motivation for this question, “magic state” distillation procedures can reduce the general fault-tolerance problem to that of performing fault-tolerant Clifford group circuits.     

多跳远程量子态制备

多跳远程量子态制备在量子无线网络、长距离量子信息传输中有重要价值。融合多跳隐形传态和远程态制备的思想，提出一个多跳远程任意单量子态制备协议。在每一跳中都以三粒子非最大纠缠GHz态为量子信道，利用远程态制备方法，原始单量子态通过中间节点逐跳被制备，每跳恢复的态被用着下一跳被制备的态。通过对单跳和两跳制备的分析，获得了[n]跳制备后方案成功的概率。在协议中，仅涉及到Pauli算子、单粒子测量和前馈策略，因此该方案易于物理实现。     

Cyclic quantum teleportation

We propose a scheme of cyclic quantum teleportation for three unknown qubits using six-qubit maximally entangled state as the quantum channel. Suppose there are three observers Alice, Bob and Charlie, each of them has been given a quantum system such as a photon or spin-\(\frac{1}{2}\) particle, prepared in state unknown to them. We show how to implement the cyclic quantum teleportation where Alice can transfer her single-qubit state of qubit a to Bob, Bob can transfer his single-qubit state of qubit b to Charlie and Charlie can also transfer his single-qubit state of qubit c to Alice. We can also implement the cyclic quantum teleportation with \(N\geqslant 3\) observers by constructing a 2N-qubit maximally entangled state as the quantum channel. By changing the quantum channel, we can change the direction of teleportation. Therefore, our scheme can realize teleportation in quantum information networks with N observers in different directions, and the security of our scheme is also investigated at the end of the paper.     

Cyclic joint remote state preparation in noisy environment

We propose a scheme of cyclic joint remote state preparation for three sides, which takes advantage of three GHZ states to compose product state as quantum channel. Suppose there are six legitimate participants, says Alice, Bob, Charlie, David, Emma and Fred in the scheme. It can be shown that Alice and David can remotely prepare a single-qubit state on Bob’s side; meanwhile, Bob and Emma can remotely prepare a desired quantum state on Charlie’s side, and Charlie and Fred can also remotely prepare a single-qubit state on Alice’s side at the same time. Further, it can be achieved in the opposite direction of the cycle by changing the quantum channel. Based on it, we generalize this protocol to \(N (N\ge 3)\) sides utilizing three multi-qubit GHZ-type states as quantum channel. Therefore, the scheme can achieve cyclic joint remote state preparation, which remotely prepares N states in quantum network with N-party, simultaneously. In addition, we consider that the effect of amplitude-damping noise of the initial states is prepared in four different laboratory. Clearly, we use fidelity to describe how much information has been lost in the cyclic process. Our investigation about the effect of noise shows that the preparing of the initial state in different laboratories will affect the loss of information.     

Automatic translation of quantum circuits to optimized one-way quantum computation patterns

One-way quantum computation (1WQC) is a model of universal quantum computations in which a specific highly entangled state called a cluster state (or graph state) allows for quantum computation by only single-qubit measurements. The needed computations in this model are organized as measurement patterns. Previously, an automatic approach to extract a 1WQC pattern from a quantum circuit has been proposed. It takes a quantum circuit consisting of CZ and \(J(\alpha )\) gates and translates it into an optimized 1WQC pattern. However, the quantum synthesis algorithms usually decompose circuits using a library containing CNOT and any single-qubit gates. In this paper, we show how this approach can be modified in a way that it can take a circuit consisting of CNOT and any single-qubit gates to produce an optimized 1WQC pattern. The single-qubit gates are first automatically \(J\) -decomposed and then added to the measurement patterns. Moreover, a new optimization technique is proposed by presenting some algorithms to add Pauli gates to the measurement patterns directly, i.e., without their \(J\) -decomposition which leads to more compact patterns for these gates. Using these algorithms, an improved approach for adding single-qubit gates to measurement patterns is proposed. The optimized pattern of CNOT gates is directly added to the measurement patterns. Experimental results show that the proposed approach can efficiently produce optimized patterns for quantum circuits and that adding CNOT gates directly to the measurement patterns decreases the translation runtime.     

量子隐形传态的通用线路

EPR态作为最基本的量子纠缠态,在量子隐形传态中起着重要作用.研究适应任意类型EPR通道的单量子比特隐形传送通用线路,并推广到任意N比特量子隐形传送通用线路.首先设计出4种EPR态,分别作为量子通道的单比特量子隐形传态,通过分析EPR量子通道与量子操作门之间的关系,设计一种单比特通用线路;然后,设计两比特的标准量子隐形传态线路,并用Mathematica进行仿真验证线路的正确性,再把它推广到N比特量子隐形传送线路;最后,将单量子比特通用线路与N比特量子隐形传送线路进行融合,最终设计出任意N比特量子隐形传送通用线路.N粒子量子比特通用线路通过信息接受者进行带参数的幺正变换,其中,参数由制备出的EPR对类型确定,解决了因EPR制备中心出错导致的信息传送失败问题.