离子阱中共线两离子基本量子逻辑门的实现

运用量子理论,在Paul阱中共线两离子系统的精确解的基础上,结合量子编码方法,讨论了囚禁两离子系统量子非门(单比特逻辑非门、两比特逻辑非门)实现的理论方法,提出利用质心振动模和两离子构建量子与门的理论方法(不需第三个离子),通过分析,证明了囚禁两离子系统在相对量子数l=1时,可制备为单比特量子非门和量子与门的线性叠加,可以完成并行量子逻辑操作,量子非门和量子与门是构成量子计算机制基本结构单元,值得我们在量子信息实验研究中加以考虑.     

基于频率调制激光驱动的囚禁离子几何相位逻辑门

为了避免激光相位的起伏对几何相位逻辑门保真度的影响, 提出一种基于囚禁离子的量子几何相位逻辑门的新方案。该机制是利用一束频率调制的行波激光场作用于两个囚禁离子上实现的。它的优点有：操作简单,仅需一步就能实现。不灵敏于激光场的相位也不需要对囚禁离子进行个别寻址。     

单离子阱中基本量子逻辑单元的实现

建议了一种利用单个囚禁冷却离子实现基本量子逻辑门操作(单比特门和两比特受控旋转门)的理论方法,通过数值计算给出了各种相关实验参量的合理设置要求.在这一方案中,量子逻辑门的操作既不要求离子辅助能级的参与,也不限定只在弱耦合的LambDicke区内进行,因而将更容易地为实验所实现 关键词： 量子计算机 受控量子逻辑门操作 LambDicke耦合参数     

基于频率调制激光驱动的囚禁离子几何相位逻辑门

为了避免激光相位的起伏对几何相位逻辑门保真度的影响,提出一种基于囚禁离子的量子几何相位逻辑门的新方案.该方案是利用一束频率调制的行波激光场作用于两个囚禁离子上实现的.它的优点有:操作简单,仅需一步就能实现,不灵敏于激光场的相位也不需要对囚禁离子进行个别寻址.     

飞秒激光直写光量子逻辑门

量子比特在同一时刻可处于所有可能状态上的叠加特性使得量子计算机具有天然的并行计算能力,在处理某些特定问题时具有超越经典计算机的明显优势.飞秒激光直写技术因其具有单步骤高效加工真三维光波导回路的能力,在制备通用型集成光量子计算机的基本单元—量子逻辑门中发挥着越来越重要的作用.本文综述了飞秒激光直写由定向耦合器构成的光量子比特逻辑门的进展.主要包括定向耦合器的功能、构成、直写和性能表征,集成波片、哈达玛门和泡利交换门等单量子比特逻辑门、受控非门和受控相位门等两量子比特逻辑门的直写加工,并对飞秒激光加工三量子比特逻辑门进行了展望.     

囚禁离子非线性Jaynes-Cummings模型量子场熵演化特性

利用VonNeuuman量子约化熵理论研究了驻波激光场与囚禁在谐振势中的离子单量子共振相互作用系统中量子场熵的时间演化特性,通过数值计算详细讨论了Lamb-Dick参数、离子质心在驻波激光场中的位置以及囚禁离子初始状态对量子场熵演化特性的影响.结果表明:Lamb-Dick参数影响囚禁离子与驻波激光场之间量子纠缠的频率和幅度,其值越大离子与光场之间的平均纠缠程度越低;随着离子质心从驻波激光场的波节向波腹移动,二者之间量子纠缠的振荡频率逐渐变慢,纠缠强度逐渐减弱;随着囚禁离子处于激发态概率的减小,离子与光场之间的量子纠缠呈现先增强后减弱的变化趋势.这些特性对于纠缠态的制备以及利用囚禁离子进行量子通讯等信息处理过程有一定的参考价值.     

REALIZATION OF QUANTUM ALGORITHMS ON SIMULATOR AND SPECTROMETER OF NMR

报道了利用NMR谱仪和NMR模拟机实现量子算法.以天然苯为样品,我们分别用500M谱仪和NMR模拟机实现了量子D-J算法,Grover搜寻算法及受控非门(C-NOT).通过比较实验谱和模拟谱发现二者能很好符合.利用NMR模拟机实现量子算法比用NMR谱仪更为方便、清晰.     

利用SPDC和PBS实现受控非门的有效方案

任意一个N量子比特逻辑运算可以由一系列单量子比特门和受控非门实现[1].因此,这两种量子逻辑门的实现是研究量子计算自然的目标.虽然单量子比特门易于实现,但是由于光子间的相互作用比较弱,所以很难实现受控非门的操作.本文基于T.B.Pittman[2]与A.L. Migdall[3]等人的工作,提出了利用自发参量下转换(SPDC)过程采用多点延时探测触发的方法获得高效单光子源,提高实现受控非门效率的理论方案.     

相干原子束-相干腔场相互作用系统中量子信息的交换传递

利用演化因子给出了相干原子束与相干腔场相互作用系统的演化规律.研究了其相互作用过程,结果表明:量子信息不但可以在相干原子与相干腔场之间相互交换,而且可以在不同相干腔场之间传递.还发现:在普遍情况下,信息交换传递的条件与原子跃迁的频率(ωa,k)及其相对相位(ξ)、光场的频率(ωf,k)及其相对相位(η)、原子与光场的耦合强度(g)和相互作用时间(t)等均有关,但当原子与光场发生共振相互作用时,其条件仅与g、t有关.     

在离子阱体系中通过Bell态来产生簇态

我们对已存在的在离子阱体系中产生簇态的方案进行修改.本文中提出的方案是基于Bell态和控制相位门(cz门)的实现.通过Bell态和控制相位门,我们就可以产生4比特(qubit)以及6比特的簇态.     

A scheme of quantum phase gate for trapped ion

We propose a scheme to implement two-qubit controlled quantum phase gate(CQPG) via a single trapped two-level ion located in the standing wave field of a quantum cavity, in which the trap works beyond the Lamb--Dicke limit. When the light field is resonant with the atomic transition $|g\rangle\leftrightarrow|e\rangle$ of the ion located at the antinode of the standing wave, we can perform CQPG between the internal and external states of the trapped ion; while the frequency of the light field is chosen to be resonant with the first red sideband of the collective vibrational mode of the ion located at the node of the standing wave, we can perform CQPG between the cavity mode and the collective vibrational mode of the trapped ion. Neither the Lamb--Dicke approximation nor the assistant classical laser is needed. Also we can generate a GHZ state if assisted with a classical laser.     

用激光-二能级原子系统实现一位通用量子逻辑门

使用代数动力学方法，对激光-二能级原子系统的含时薛定谔方程进行求解.该系统哈密顿量具有SU(2)代数结构，得到了严格解.基于严格解，适当调节单模激光场的频率和振幅以及短脉冲激光与二能级原子的二阶虚光子作用强度，可实现一位通用量子逻辑门. 关键词： 代数动力学 激光-二能级原子系统 一位量子逻辑门     

How to control a geometric quantum gate

In this paper, we detail the theoretical ideas which are used to explain the mechanism of the laser controlling the geometric quantum gates introduced in the work by Ekert et al. (Ekert A, Ericsson M, Hayden P, Inanori H, Jones J A, Oi D K L and Vedral V 2000 J. Mod. Opt. 47 2501). We have introduced a two-level Hamiltonian system, and directed to solve this system, and then obtained the probability distribution of this two-level system. We also show the relationships between the external laser fields and the transition of the qubit in the two-qubit controlled-phase gate, and how the transition of the qubit depends on the external laser fields and the states of the controlled qubit.     

A scheme for the implementation of unconventional geometric phase gates with trapped ions

We propose a scheme for the realization of unconventional geometric two-qubit phase gates with two identical two-level ions, In the present scheme, the two ions are simultaneously illuminated by a standing-wave laser pulse with its pulse frequency being tuned to the ionic transition. The gate operation time can be much shorter, making the system robust against decoherence. In addition, we choose the appropriate experimental parameters to construct the geometric phase gate in one step, and thus avoid implementing the pure geometric single qubit operation.[第一段]     

One step to generate quantum controlled phase-shift gate using a trapped ion

This paper presents a very simple scheme for generating quantum controlled phase-shift gate with only one step by using the two vibrational modes of a trapped ion as the two qubits. The scheme couples two vibration degrees of freedom coupled with a suitable chosen laser excitation via the ionic states.     

激光距离选通成像门宽对图像信噪比影响

为了解不同激光测距精度下的选通成像信噪比,本文利用外场实验系统对不同门宽条件下的图像信噪比进行了分析。首先,根据激光距离选通成像理论建立作用距离模型,初步确定系统各项参数。在此基础上,构建外场实验系统,并利用实验系统进行外场实验研究。对不同门宽条件下的图像进行分析对比,获得门宽与图像信噪比关系曲线。实验结果表明:在门宽2 μs范围内,图像信噪比≥8,图像质量满足自动识别要求,充分证明了距离选通成像系统对测距精度要求较低,完全满足实际应用需求。     

Realization of Toffoli gate operation using four-level atoms in cavity QED system

This paper proposes a scheme for realization of a three-qubit Toffoli gate operation using three four-level atoms by a selective atom--field interaction in a cavity quantum electrodynamics system. In the proposed protocol, the quantum information is encoded on the stable ground states of atoms, and atomic spontaneous emission is negligible as the large atom--cavity detuning effectively suppresses the spontaneous decay of the atoms. The influence of the dissipation on fidelity and success probability of the three-qubit Toffoli gate is also discussed. The scheme can also be applied to realize an N-qubit Toffoli gate and the interaction time required does not rise with increasing the number of qubits.     

Quantum computation with ions in microscopic traps

We discuss a possible experimental realization of fast quantum gates with high fidelity with ions confined in microscopic traps. The original proposal of this physical system for quantum computation comes from Cirac and Zoller (Nature 404, 579 (2000)). In this paper we analyse a sensitivity of the ion-trap quantum gate on various experimental parameters which was omitted in the original proposal. We address imprecision of laser pulses, impact of photon scattering, nonzero temperature effects and influence of laser intensity fluctuations on the total fidelity of the two-qubit phase gate.     

One-step implementation of a multi-target-qubit controlled phase gate with cat-state qubits in circuit QED

We propose a single-step implementation of a muti-target-qubit controlled phase gate with one catstate qubit (cqubit) simultaneously controlling n–1 target cqubits. The two logic states of a cqubit are represented by two orthogonal cat states of a single cavity mode. In this proposal, the gate is implemented with n microwave cavities coupled to a superconducting transmon qutrit. Because the qutrit remains in the ground state during the gate operation, decoherence caused due to the qutrit’s energy relaxation and dephasing is greatly suppressed. The gate implementation is quite simple because only a single-step operation is needed and neither classical pulse nor measurement is required. Numerical simulations demonstrate that high-fidelity realization of a controlled phase gate with one cqubit simultaneously controlling two target cqubits is feasible with present circuit QED technology. This proposal can be extended to a wide range of physical systems to realize the proposed gate, such as multiple microwave or optical cavities coupled to a natural or artificial three-level atom.     

利用大失谐腔场中的两个原子实现量子相位门

本文讨论同时囚禁于单模、大失谐腔场中两个不同原子构成的系统,结论指出:只要仔细选择两不同原子的跃迁频率差、原子与腔场相互作用时间,可实现一个快速的量子相位门。这一方案不需要辅助的原子能级。