共查询到17条相似文献,搜索用时 62 毫秒
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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. 相似文献
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量子逻辑网络的核磁共振实现 总被引:1,自引:1,他引:0
利用相位相反技术,设计出了实现精确的CN门的脉冲序列;构造了三量子位的双重控制相位旋转门(CCS门),它是将核磁共振(NMR)实现Grover量子算法从二量子位推广到三量子位的关键逻辑门,而且,依此方法,可以用NMR实现N量子位的Grover量子算法;还给出了量子Toffoli门以及量子态的各种对称操作的逻辑部件。所有这些逻辑操作都是构建量子态工程的工具。文中大部分脉冲序列己经在实验中得到验证,这些结果对于量子计算的理论研究和实验实现都具有现实意义。 相似文献
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针对量子系统的联合消相干模型,可以找到一些不受消相干错误影响的系统状态,这种状态被称为相干保持态,所有相干保持态构成的空间就称为无消相干子空间(decoherencefreesubspace,缩写为DFS).利用DFS的特性可以实现自动容错的量子避错码.首先提出一种DFS的定义,并且以定理的形式证明其他DFS的定义都是等价的.然后给出了DFS的存在性定理.最后利用群论的方法设计一种构造DFS的简单方法
关键词:
相干保持态
无消相干子空间
量子避错码
容错量子计算 相似文献
4.
过去的二十年中,量子信息相关研究取得了显著的进展,重要的理论和实验工作不断涌现.与其他量子信息处理系统相比,基于自旋动力学的核磁共振系统,不仅具有丰富而且成熟的控制技术,还拥有相干时间长、脉冲操控精确、保真度高等优点.这也是核磁共振体量子系统能够精确操控多达12比特的量子系统的原因.因此,核磁共振量子处理器在量子信息领域一直扮演着重要角色.本文介绍核磁共振量子计算的基本原理和一些新研究进展.研究的新进展主要包括量子噪声注入技术、量子机器学习在核磁共振平台上的实验演示、高能物理和拓扑序的量子模拟以及核磁共振量子云平台等.最后讨论了液态核磁共振的发展前景和发展瓶颈,并对未来发展方向提出展望. 相似文献
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核磁共振量子计算机与并行量子计算 总被引:1,自引:0,他引:1
在本文,我们首先回顾了量子计算的发展历史,阐述了核磁共振量子计算的原理.在叙述了利用有效纯态方法进行核磁共振量子计算之后,我们阐述了利用混合态进行核磁共振的量子计算的方法.首先是刘维尔量子计算方法,它是由Madi,Brushweiler,Ernst等人1998年提出的,在这一模式中,可以对搜索算法进行加速算法,Brushweilet。提出了一个指数速度的搜索算法.我们在3个比特的量子计算机中实现了这一搜索算法.我们在这一模式中提出了一个只需要一次搜索即可找标记物的直接拿取算法,并且在7个比特的核磁共振的量子计算机中实现了这一直接拿取算法.本文提出了在一个核磁共振量子计算机,或者更一般地一个系统量子计算机中实现多个量子计算机的并行计算.我们着重对量子搜索算法和Shor。的大数分解算法进行了并行实现.在并行量子计算中,一部分量子比特处在纯态,一部分量子比特处在混合态.如果所有的量子比特都处在纯态上,则就是有效纯态量子计算,如果所有的量子比特都处在混合态上,则就是刘维尔量子计算.在这两个极限中间,相当于2个到N/2个量子计算机的并行计算.量子搜索方法可以很有效地进行并行计算,而Shor算法则只能在小的范围内进行并行计算. 相似文献
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随着量子信息与量子计算科学的发展,量子信息处理器被广泛地用于量子计算、量子模拟、量子度量等方面的研究.为了能在实验上实现这些日益复杂的方案,将量子计算机的潜能转化成现实,需要不断提高可操控的量子体系比特位数,实现更复杂的量子操控.核磁共振自旋体系作为一个优秀的量子实验测试平台,提供了丰富而又精密的量子操控手段.近几年来在此平台上进行了不少的多量子比特实验,发展并积累了一系列的多量子比特实验技术.本文首先阐述了核磁共振体系多量子比特实验中的实验困难,然后结合7量子比特标记赝纯态制备以及其他有关实验,对多比特实验过程中应用到的实验技术进行介绍.最后对核磁共振体系多量子比特实验技术方向的进一步研究进行了总结和展望. 相似文献
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从两量子位核磁共振量子处理器物理模型出发,利用Raedt小组提出的自旋-1/2代数理论,根据量子控制非门的定义及Grover量子算法原理,介绍了量子控制非门的4种不同脉冲序列及两量子位Grover量子算法的两种不同脉冲序列的设计过程,通过数值求解含时薛定谔方程模拟量子控制非门和两量子位Grover量子算法,等价于执行量... 相似文献
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3 刘维尔量子计算中的指数加快的搜索算法———Bruschweiler算法3 .1 Bruschweiler算法[4 5]与Grover搜索算法一样 ,Bruschweiler算法也是在无序数据库中寻找目标态 .对于搜寻问题可以总结为 :对于输入态x ,除了当x=z时 ,f(z) =1,其余的 f(x) =0 .z是我们要寻找的目标 .在经典计算机中 ,大概要O(N)步 ;用Grover算法大概要O(N )步 ;用Bruschweiler算法大概仅需要O(n)步 .其中 ,N =2 n.Bruschweiler利用NMR是自旋系综的特点 ,将初始态制备成不同自旋态的线性叠加 ,使初始态处于完全混合态 ,当U变换作用其上时 ,不同的自旋态在做不同… 相似文献
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Three-body interaction plays an important role in many-body physics, and quantum computer is efficient in simulating many-body
interactions. We have experimentally demonstrated the general three-body interactions in a three-qubit nuclear magnetic resonance
ensemble quantum computer. Using a nuclear magnetic resonance computer we implemented general forms of three-body interactions
including σ
x
1
σ
z
2
σ
x
3 and σ
x
1
σ
z
2
σ
y
3 The results show good agreement between theory and experiment. We have also given a concise and practical formula for a general
n-body interaction in terms of one-and two-body interactions.
Supported by the National Natural Science Foundation of China (Grant Nos. 10374010 and 10325521) and the National Basic Research
Program of China (Grant No. 2006CB921106) 相似文献
13.
Strong and extremely homogeneous static magnetic field is usually required for high-resolution nu-clear magnetic resonance (NMR). However, in the cases of in vivo and so on, the magnetic field inho-mogeneity owing to magnetic susceptibility variation in samples is unavoidable and hard to eliminate by conventional methods such as shimming. Recently, intermolecular multiple quantum coherences (iMQCs) have been employed to eliminate inhomogeneous broadening and obtain high-resolution NMR spectra, especially for in vivo samples. Compared to other high-resolution NMR methods, iMQC method exhibits its unique feature and advantage. It simultaneously holds information of chemical shifts, multiplet structures, coupling constants, and relative peak areas. All the information is often used to analyze and characterize molecular structures in conventional one-dimensional NMR spec-troscopy. In this work, recent technical developments including our results in this field are summarized; the high-resolution mechanism is analyzed and comparison with other methods based on interactions between spins is made; comments on the current situation and outlook on the research directions are also made. 相似文献
14.
Use of dipolar and quadrupolar couplings for quantum information processing (QIP) by nuclear magnetic resonance (NMR) is described.
In these cases, instead of the individual spins being qubits, the 2
n
energy levels of the spin-system can be treated as an n-qubit system. It is demonstrated that QIP in such systems can be carried out using transition-selective pulses, in CH3CN, 13CH3CN, 7Li (I=3/2) and 133Cs (I=7/2), oriented in liquid crystals yielding 2 and 3 qubit systems. Creation of pseudopure states, implementation of logic
gates and arithmetic operations (half-adder and subtractor) have been carried out in these systems using transition-selective
pulses. 相似文献
15.
Zhang Jingfu Xie Jingyi Wang Chuan Deng Zhiwei Lu Zhiheng Long Guilu 《中国科学G辑(英文版)》2005,48(2):706-715
A multiple round quantum dense coding scheme based on the quantum phase estimation algorithm is proposed and implemented in
a three qubit nuclear magnetic resonance (NMR) quantum computer. Using anm+1 qubit system, Bod can transmit one of 2
m+1 messages to Alice, through manipulating only one qubit and exchanging it between Alice and Bob form rounds. The information capacity is enhanced tom+1 bits as compared tom bits in a classical scheme. The scheme has been demonstrated in NMR system, and the experimental results show a good agreement
between theory and experiment. 相似文献
16.
Implementation of a multiple round quantum dense coding using nuclear magnetic resonance 总被引:1,自引:0,他引:1
~~Implementation of a multiple round quantum dense coding using nuclear magnetic resonance1. Bennett, C. H., Wiesner, S. J., Communication via one- and two-particle operators on Einstein-Podolsky-Rosen states, Phys. Rev. Lett., 1992, 69(20): 2881-2884.
2. Mattle, K., Weinfurter, H., Kwiat, P. G. et al., Dense coding in experimental quantum communication, Phys. Rev. Lett., 1996, 76(25): 4656-4659.
3. Fang, X. M., Zhu, X. W., Feng, M. et al., Experimental implementation of dens… 相似文献
17.
Study on signal intensity of low field nuclear magnetic resonance via an indirect coupling measurement 下载免费PDF全文
We carry out an ultra-low-field nuclear magnetic resonance (NMR) experiment based on high-T c superconducting quantum interference devices (SQUIDs). The measurement field is in a micro-tesla range (~10 μT-100 μT) and the experiment is conducted in a home-made magnetically-shielded-room (MSR). The measurements are performed by the indirect coupling method in which the signal of nuclei precession is indirectly coupled to the SQUID through a tuned copper coil transformer. In such an arrangement, the interferences of applied measurement and polarization field to the SQUID sensor are avoided and the performance of the SQUID is not destroyed. In order to compare the detection sensitivity obtained by using the SQUID with that achieved using a conventional low-noise-amplifier, we perform the measurements using a commercial room temperature amplifier. The results show that in a wide frequency range (~1 kHz-10 kHz) the measurements with the SQUID sensor exhibit a higher signal-to-noise ratio. Further, we discuss the dependence of NMR peak magnitude on measurement frequency. We attribute the reduction of the peak magnitude at high frequency to the increased field inhomogeneity as the measurement field increases. This is verified by compensating the field gradient using three sets of gradient coils. 相似文献