制备三量子位和四量子位核磁共振等效纯态

基于时间平均法,给出了在同核系统中制备三量子位和四量子位核磁共振等效纯态的方案.利用Λn(not)门,本文的方案大大减少了制备等效纯态所需的操作次数在三同核系统中制备三量子位核磁共振等效纯态只需三次操作,在四同核系统中制备四量子位核磁共振等效纯态只需五次操作.然后在一个链状耦合的同核系统中实验制备三量子位核磁共振等效纯态,验证了本文的方案;并且给出了四量子位方案的模拟结果谱图.     

两量子位Grover量子算法NMR脉冲序列参量的研究

从两量子位核磁共振量子计算机物理模型出发,通过解单体含时薛定谔方程和解两体含时薛定谔方程,提出了Grover量子算法核磁共振脉冲序列参量设定的两种规则,给出了具体参量取值,并进行了数值仿真,仿真结果表明:解两体薛定谔方程给出的参量设定规则,能使两量子位量子搜索的目标态是纯基态,目标态的z分量期望值精确度达到在小数点后三位与理论值完全相同,验证了我们提出的参量设定规则的正确性.     

两量子位Grover量子算法NMR脉冲序列参量的研究

从两量子位核磁共振量子计算机物理模型出发,通过解单体含时薛定谔方程和解两体含时薛定谔方程,提出了Grover量子算法核磁共振脉冲序列参量设定的两种规则,给出了具体参量取值,并进行了数值仿真,仿真结果表明：解两体薛定谔方程给出的参量设定规则,能使两量子位量子搜索的目标态是纯基态,目标态的z分量期望值精确度达到在小数点后三位与理论值完全相同,验证了我们提出的参量设定规则的正确性.     

Cluster态的核磁共振实验制备

利用一种优化的幺正算符制备了一种高度纠缠态——cluster态,这个优化的幺正算符因为只需要施加非选择性脉冲,其所用的时间被明显缩短.该文选择一个三量子位的自旋体系,在核磁共振仪器上进行了实验验证,实验过程中先制备了一个三量子位的纯态,然后通过施加优化的幺正算符即可得到三量子位的cluster态,实验结果证明了优化幺正算符的有效性.     

新的summing算法的核磁共振实验实现

本文报导了一种新的summing算法的核磁共振实验实现.实验中我们用到了四个量子位的核自旋体系,其中两个量子位构成输入寄存器,另两个量子位构成输出寄存器.最后的实验结果只需通过测量输出寄存器中核自旋的谱线获得.     

利用仲氢诱导极化技术实现 Deutsch算法

核磁共振系统是实现量子计算的有效物理体系之一．但是随着量子位数的不断增加,运用核磁共振技术实现计算任务存在明显的局限性,原因之一是量子计算的初始态-赝纯态,随着量子位数的增加,信号指数性的衰减,量子位数越多制备赝纯态所需的脉冲序列越复杂,越不容易实现,不利于量子位数的扩展;另外,由于核磁共振中制备的赝纯态实际上也是一种混合态,用于实现量子信息任务时存在一定的争议．该文介绍的利用仲氢诱导极化技术(PHIP)制备出的实验初态,能够解决初态处于混合态的问题,并且信号强度显著增强,作者利用此态实现了 ALTADENA 条件下的两量子位的 Deutsch-Jozsa 量子算法和 PASADENA 条件下的三量子位的Deutsch-Like 量子算法．
     

Cluster 态的核磁共振实验制备

利用一种优化的幺正算符制备了一种高度纠缠态--cluster 态,这个优化的幺正算符因为只需要施加非选择性脉冲,其所用的时间被明显缩短．该文选择一个三量子位的自旋体系,在核磁共振仪器上进行了实验验证,实验过程中先制备了一个三量子位的纯态,然后通过施加优化的幺正算符即可得到三量子位的cluster 态,实验结果证明了优化幺正算符的有效性．     

多量子比特核磁共振体系的实验操控技术

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.     

核磁共振量子计算机与并行量子计算

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．     

新的summing算法的核磁共振实验实现

本报导了一种新的summing算法的核磁共振实验实现。实验中我们用到了四个量子位的核自旋体系，其中两个量子位构成输入寄存器，另两个量子位构成输出寄存器。最后的实验结果只需通过测量输出寄存器中核自旋的谱线获得。     

Quantum information processing by NMR using a 5-qubit system formed by dipolar coupled spins in an oriented molecule

Quantum information processing by NMR with small number of qubits is well established. Scaling to higher number of qubits is hindered by two major requirements (i) mutual coupling among qubits and (ii) qubit addressability. It has been demonstrated that mutual coupling can be increased by using residual dipolar couplings among spins by orienting the spin system in a liquid crystalline matrix. In such a case, the heteronuclear spins are weakly coupled, but the homonuclear spins often become strongly coupled. In such circumstances, the strongly coupled spins, which yield second order spectra, can no longer be individually treated as qubits. However, it has been demonstrated elsewhere, that the 2(N) energy levels of a strongly coupled N spin-1/2 system can be treated as an N-qubit system. For this purpose the various transitions have to be identified to well defined energy levels. This paper consists of two parts. In the first part, the energy level diagram of a heteronuclear 5-spin system is obtained by using a newly developed heteronuclear z-cosy (HET-Z-COSY) experiment. In the second part, implementation of logic gates, preparation of pseudopure states, creation of entanglement, and entanglement transfer is demonstrated, validating the use of such systems for quantum information processing.     

The stabilizer for..-qubit symmetric states

The stabilizer group for an n-qubit state |Φ is the set of all invertible local operators(ILO) g = g1g2···gn,gi 2 GL(2,C) such that |Φ= g|Φ. Recently, Gour et al. [Gour G, Kraus B and Wallach N R 2017 J. Math. Phys. 58092204] presented that almost all n-qubit states jyi own a trivial stabilizer group when n≥5. In this article, we consider the case when the stabilizer group of an n-qubit symmetric pure state jyi is trivial. First we show that the stabilizer group for an n-qubit symmetric pure state |Φ is nontrivial when n≤4. Then we present a class of n-qubit symmetric states |Ψ with a trivial stabilizer group when n≥5. Finally, we propose a conjecture and prove that an n-qubit symmetric pure state owns a trivial stabilizer group when its diversity number is bigger than 5 under the conjecture we make, which confirms the main result of Gour et al. partly.     

Disentanglement of 3-qubit states with stochastic dephasing

The effect of stochastic dephasing on the entanglement of 3-qubit states is analyzed. We find that the extent to which the entanglement vanishes depends not only on the strength of the stochastic dephasing, but also on the structure of states of concern under decoherence induced by the stochastic dephasing. The linear entropy used to measure coherence loss is evaluated.     

A generalized tripartite scheme for splitting an arbitrary 2-qubit state with three 2-qubit partially entangled states and the Kraus measurement

We put forward a generalized tripartite scheme for splitting an arbitrary 2-qubit pure state with three 2-qubit non-maximally en-tangled states as quantum channels.The scheme for the first time incorporates the Kraus measurement into quantum information splitting scheme.In contrast to the similar scheme using the same quantum channels and the ancilla-entangled measurement,our scheme is superior in terms of operation and complexity,success probability,resource consumption and effciency.     

Benchmarking quantum control methods on a 12-qubit system

In this Letter, we present an experimental benchmark of operational control methods in quantum information processors extended up to 12 qubits. We implement universal control of this large Hilbert space using two complementary approaches and discuss their accuracy and scalability. Despite decoherence, we were able to reach a 12-coherence state (or a 12-qubit pseudopure cat state) and decode it into an 11 qubit plus one qutrit pseudopure state using liquid state nuclear magnetic resonance quantum information processors.     

基于腔QED制备四粒子supersinglets

在双光子跃迁下,本文基于腔量子电动力学(QED)系统提出了一种制备4粒子supersinglets的方案.方案要求腔场最初处于真空态,依次与四个腔场发生共振作用的三能级原子最初处于激发态.分析和讨论了该方案的可行性以及原子-腔场的耦合常数对保真度的影响.结果表明：1)该态保真度的值随原子与腔场相互作用时间的不同而不同,选择合适的原子-腔场相互作用过程以及对原子态的探测,可获得具有最大保真度的纠缠态;2)失谐量等于零时,耦合常数越大,保真度对原子与腔场相互作用的时间越敏感.     

Discussion of the entanglement classification of a 4-qubit pure state

We classify 4-qubit pure states under the stochastic local operation and classical communication (SLOCC). There exist twenty three essentially different classes of states, giving rise to a four-graded partially ordered structure. We also give the criterion to judge which class an arbitrary 4-qubit state belongs to. We re-classify the 4-qubit pure state into 2×2×4, 4×4 aspects. Finally, we give our analysis of the classification difference of methods for the 3-qubit pure state.     

Quantum teleportation using entangled 3-qubit states and the ‘magic bases’

We study quantum teleportation of single qubit information state using 3-qubit general entangled states. We propose a set of 8 GHZ-like states which gives (i) standard quantum teleportation (SQT) involving two parties and 3-qubit Bell state measurement (BSM) and (ii) controlled quantum teleportation (CQT) involving three parties, 2-qubit BSM and an independent measurement on one qubit. Both are obtained with perfect success and fidelity and with no restriction on destinations (receiver) of any of the three entangled qubits. For SQT, for each designated one qubit which is one of a pair going to Alice, we obtain a magic basis containing eight basis states. The eight basis states can be put in two groups of four, such that states of one group are identical with the corresponding GHZ-like states and states of the other differ from the corresponding GHZ-like states by the same phase factor. These basis states can be put in two different groups of four-states each, such that if any entangled state is a superposition of these with coefficients of each group having the same phase, perfect SQT results. Also, for perfect CQT, with each set of given destinations of entangled qubits, we find a different magic basis. If no restriction on destinations of any entangled qubit exists, three magic semi-bases, each with four basis states, are obtained, which lead to perfect SQT. For perfect CQT, with no restriction on entangled qubits, we find four magic quarter-bases, each having two basis states. This gives perfect SQT also. We also obtain expressions for co-concurrences and conditional concurrences.     

Asymmetric Bidirectional 3 ⇔ 2 Qubit Teleportation Protocol Between Alice and Bob Via 9-qubit Cluster State

International Journal of Theoretical Physics - In this paper we present a protocol to perform the task of a bilateral exchange of entanglements between two parties in the case where one of the...