量子Fourier变换在实现Deutsch-Jozsa算法中的应用

提出利用量子Fourier变换解决Deutsch-Jozsa算法问题的观点.结合量子Fourier变换和Deutsch-Jozsa算法的量子电路,找到一种利用量子Fourier变换解决Deutsch-Jozsa算法新的量子电路,并考察该量子电路中各个线路的量子状态,结合算法对该量子线路的状态进行研究.结果表明:利用量子Fourier变换解决Deutsch问题,能够有效地提高运算速度,节省运算时间.     

量子计算与量子电路仿真技术

采用量子计算研究中最具代表性的电路模型模拟量子计算过程,实现Deutsch算法和量子Fourier变换的演算,构建了量子信息与计算的仿真平台雏形.实验平台采用量子寄存器结构作为存储媒介,在空间上优于矩阵形式,运算过程采用位操作避免了大量乘法运算的时间,实验结果可直接被其他重要量子算法所引用.采用新型结构减少了时间和空间耗费,运算过程更加简单直观,为平台的进一步完善提供了基础.     

基于真值表演算的四量子电路综合方法

为了能以较小的代价高效地自动构造量子可逆逻辑电路,提出了一种新颖的四量子可逆逻辑综合方法.该方法首先将一个四量子电路的函数表示成真值表的形式;然后利用传统的递归思想,通过对换演算,将四量子电路映射函数的真值表分解成2块相互独立的三量子电路映射函数的真值表;再查找相应的最优三量子电路,直接生成相关电路;最后将对换运算的电路并入该电路,经过局部优化即可生成最终电路.分析结果表明,用该方法综合四量子电路能大幅减少TOF门的数量,平均需要15.74个TOF门,最多只需24个TOF门.同时该算法避免了穷举法所需的时空复杂度太大的问题,便于经典计算机实现.     

自旋1/2态下的量子逻辑变换

作者利用对自旋算符的量子线性变换理论，提供了一种考察自旋1/2态下的量子逻辑门变换的一种有效方法，并给出了几个基本量子逻辑操作的变换表达式。     

纳米微结构的输运过程研究

用一维纳米微结构体系的本征值和本征波函数定义量子谱函数.这种量子谱函数的Fourier变换,包含了在该体系中将粒子从一个点输运到另一个点的过程中所经历的经典轨道的许多信息.研究的结果为探讨纳米微结构中的经典物理和量子物理之间的对应关系提供了可靠的依据.     

量子乘法器的设计及其实现方法

乘法器在数字信号处理和数字通信领域应用广泛,如何实现快速高效的乘法器关系着整个系统的运算速度。提出了一种新颖的量子乘法器设计方法,利用量子门设计一位量子全加器,并将n个一位量子全加器叠加在一起设计n位量子全加器,实现2个n位二进制数的加和;再利用2个控制非门设计置零电路,并使用置零电路设计量子右移算子;对二进制数乘法步骤进行改进,利用量子全加器和量子右移算子设计量子乘法器,同时设计实现此乘法器的量子线路。时间复杂度分析结果表明,本方法与目前最高效的量子乘法器具有相同的时间复杂度,并具有更简洁的实现方法。     

利用量子计算网络实现量子远距传态

利用处于纠缠的一对粒子，作为量子位传态通道，实现远程量子传态，并构造出量子计算网络。     

介观含源RLC并联电路的量子涨落

由于耗散的存在，介观RLC并联电路中的磁通量和电荷不是一对线性厄米算符，因此，构造了一对正则变量，并用该对正则变量作为算符实现了介观RLC并联电路的量子化，在外源作用下，介观RLC并联电路系统由初始本征态将演化到平称Fock态，在平移Fock态中，计算了磁通量和电荷的量子涨落。     

设计最优量子克隆机的通用方案

本文利用量子克隆机（QCM）在Bloch球表象中的描述,导出了最优态有关量子克隆机的通用幺正变换，该幺正变换仅需6个自由参数，它们的值与具体的输入态分布有关，可由Fiuráek最优化条件确定.     

二维siani台球中的量子与经典对应

研究了二维sinai台球的经典与量子的对应，运用闭合轨道理论及定态展开方法计算了傅立叶变换的量子谱．把傅立叶变换后的量子谱中峰的位置与其所对应的经典轨道长度作对照，我们发现两者之间存在着对应关系．为我们理解量子混沌性提出了新的线索．     

Efficient Scheme for Optimizing Quantum Fourier Circuits

In quantum circuits, importing of additional qubits can reduce the operation time and prevent decoherence induced by the environment. However, excessive qubits may make the quantum system vulnerable. This paper describes how to relax existing qubits without additional qubits to significantly reduce the operation time of the quantum Fourier circuit compared to a circuit without optimization. The results indicate that this scheme makes full use of the qubits relaxation. The concepts can be applied to improve similar quantum circuits and guide the physical implementations of quantum algorithms or devices.     

基于腔场耦合的超导比特的量子计算(英文)

利用超导量子比特实现量子计算在世界范围内备受理论界和实验界的关注.在这一体系中实现量子计算的明显好处是具有非常好的操控技术及容易集成化.过去10年实验的快速突破验证了体系的这些优势.在调节不同比特耦合方面,利用微波腔场耦合比特的平台已经建立起来.该综述将重点介绍如何形成等效的超导电荷比特、它和腔场的耦合,以及利用腔场耦合多个比特等内容.     

Quantum oscillations in two coupled charge qubits

A practical quantum computer, if built, would consist of a set of coupled two-level quantum systems (qubits). Among the variety of qubits implemented, solid-state qubits are of particular interest because of their potential suitability for integrated devices. A variety of qubits based on Josephson junctions have been implemented; these exploit the coherence of Cooper-pair tunnelling in the superconducting state. Despite apparent progress in the implementation of individual solid-state qubits, there have been no experimental reports of multiple qubit gates--a basic requirement for building a real quantum computer. Here we demonstrate a Josephson circuit consisting of two coupled charge qubits. Using a pulse technique, we coherently mix quantum states and observe quantum oscillations, the spectrum of which reflects interaction between the qubits. Our results demonstrate the feasibility of coupling multiple solid-state qubits, and indicate the existence of entangled two-qubit states.     

控制开放超导量子电路系统中的几何量子关联冻结和量子相干性

本文研究了开放超导量子电路系统中,含时电磁场对两超导量子比特间的几何量子关联和量子相干性的影响. 我们发现,加入磁场之后,几何量子关联被冻结的现象会出现,并且冻结的时间会随着含时电磁场的加入而得到延长. 利用迹距离的方法,我们探讨了含时电磁场对超导量子比特与环境之间量子信息流动的影响,我们发现含时电磁场可以抑制环境的影响,降低超导量子比特与环境之间的量子信息流动.     

Speeding up implementation for Shor’s factorization quantum algorithm

In this paper, based on the implementation of semiclassical quantum Fourier transform, we first propose the concept of generation vector of ternary binary representation, construct the generation function’s truth table, prove that the generation vector of ternary binary representation is one kind of k ’s NAF representation and further find that its number of nonzero is not more than [(⌈log k⌉ + 1)/2]. Then we redesign a quantum circuit for Shor’s algorithm, whose computation resource is approximately equal to that of Parker (Their requirements of elementary quantum gate are both O(⌈logN⌉³), and our circuit requires 2 qubits more than Parker’s). However, our circuit is twice as fast as Parker’s.     

电荷比特的超强藕合实现及量子态转移

基于超导量子电路中光与物质相互作用强度的可调性, 研究了库珀对盒子(Cooper-pair box, CPB)与LC谐振电路耦合的电路模型, 证明了可以通过减小CPB的约瑟夫森能量和增加LC谐振子阻抗, 实现光与物质的超强耦合(ultra-strong coupling, USC)和深度强耦合(deep-strong coupling, DSC)相互作用. 在此基础上, 进一步提出了具有一定抗噪性的 USC 双比特超导电路模型, 并以该模型作为非相干中介实现了两个Transmon系统间的量子态转移(quantum-state transfer, QST). 研究结果为在超导量子系统中实现USC相互作用提供了新的方案, 并有望进一步应用于量子调控、量子模拟和量子信息处理等领域.     

基于微腔中自生长量子点的量子光信息存储

提出一个基于微型圆盘光学谐振腔（microdisk structure cavity）中自生长量子点的量子光信号存储方案,该方案利用量子光场和量子点系综自旋态之间的Raman过程来实现长时间的量子光信号存储.该方案的主要优势在于：使用全光学Raman过程来耦合光信号和腔中量子点的导带能级,使系统有可能存在较长的相干时间.此外,这种微腔中自生长量子点的工艺比较成熟,使该方案便于实验上实现、控制和大规模集成.     

Coupling superconducting qubits via a cavity bus

Superconducting circuits are promising candidates for constructing quantum bits (qubits) in a quantum computer; single-qubit operations are now routine, and several examples of two-qubit interactions and gates have been demonstrated. These experiments show that two nearby qubits can be readily coupled with local interactions. Performing gate operations between an arbitrary pair of distant qubits is highly desirable for any quantum computer architecture, but has not yet been demonstrated. An efficient way to achieve this goal is to couple the qubits to a 'quantum bus', which distributes quantum information among the qubits. Here we show the implementation of such a quantum bus, using microwave photons confined in a transmission line cavity, to couple two superconducting qubits on opposite sides of a chip. The interaction is mediated by the exchange of virtual rather than real photons, avoiding cavity-induced loss. Using fast control of the qubits to switch the coupling effectively on and off, we demonstrate coherent transfer of quantum states between the qubits. The cavity is also used to perform multiplexed control and measurement of the qubit states. This approach can be expanded to more than two qubits, and is an attractive architecture for quantum information processing on a chip.     

Coherent quantum state storage and transfer between two phase qubits via a resonant cavity

As with classical information processing, a quantum information processor requires bits (qubits) that can be independently addressed and read out, long-term memory elements to store arbitrary quantum states, and the ability to transfer quantum information through a coherent communication bus accessible to a large number of qubits. Superconducting qubits made with scalable microfabrication techniques are a promising candidate for the realization of a large-scale quantum information processor. Although these systems have successfully passed tests of coherent coupling for up to four qubits, communication of individual quantum states between superconducting qubits via a quantum bus has not yet been realized. Here, we perform an experiment demonstrating the ability to coherently transfer quantum states between two superconducting Josephson phase qubits through a quantum bus. This quantum bus is a resonant cavity formed by an open-ended superconducting transmission line of length 7 mm. After preparing an initial quantum state with the first qubit, this quantum information is transferred and stored as a nonclassical photon state of the resonant cavity, then retrieved later by the second qubit connected to the opposite end of the cavity. Beyond simple state transfer, these results suggest that a high-quality-factor superconducting cavity could also function as a useful short-term memory element. The basic architecture presented here can be expanded, offering the possibility for the coherent interaction of a large number of superconducting qubits.