Quantum communication via controlled holes in the statistical distribution of excitations in a nanoresonator coupled to a Cooper pair box

We propose a scheme to transmit information via the statistical distribution of excitations of a nanomechanical resonator. It employs a controllable coupling between this system and a Cooper pair box. The success probability and the fidelity are calculated and compared with those obtained in an atom-field system in different regimes. Addtionaly, the scheme can also be applied to prepare low excited Fock states.     

Dissipation-Induced Information Scrambling in a Collision Model

In this paper, we present a collision model to stroboscopically simulate the dynamics of information in dissipative systems. In particular, an all-optical scheme is proposed to investigate the information scrambling of bosonic systems with Gaussian environmental states. Varying the states of environments, in the presence of dissipation, transient tripartite mutual information of system modes may show negative value, signaling the appearance of information scrambling. We also find that dynamical indivisibility based non-Markovianity plays dual roles in affecting the dynamics of information.     

Improvement of a continuous-variable measurement-device-independent quantum key distribution system via quantum scissors

We propose a new scheme to enhance the performance of the Gussian-modulated coherent-state continuous-variable measurement-device-independent quantum key distribution (CV-MDI-QKD) system via quantum scissors (QS) operation at Bob's side. As an non-deterministic amplifying setup, we firstly introduce the QS-enhanced CV-MDI-QKD protocol and then investigate the success probability of the QS operation in accordance with the equivalent one-way scheme. Afterwards, we investigate the effect of the QS operation on the proposed scheme and analyze the performance of the QS-enhanced CV-MDI-QKD system under the extreme asymmetric circumstance. Simulation results show that the QS operation can indeed improve the performance of the CV-MDI-QKD system considerably. QS-enhanced CV-MDI-QKD protocol outperforms the original CV-MDI-QKD protocol in both the maximum transmission distance and the secret key rate. Moreover, the better the performance of QS operation, the more significant the improvement of performance of the system.     

Implementation of a Controlled-Phase Gate and Deutsch-Jozsa Algorithm with Superconducting Charge Qubits in a Cavity

Based on superconducting quantum interference devices （SQUIDs） coupled to a cavity, we propose a scheme for implementing a quantum controlled-phase gate （QPG） and Deutsch-Jozsa （D J） algorithm by a controllable interaction. In the present scheme, the SQUID works in the charge regime, and the cavity field is ultilized as quantum data-bus, which is sequentially coupled to only one qubit at a time. The interaction between the selected qubit and the data bus, such as resonant and dispersive interaction, can be realized by turning the gate capacitance of each SQUID. Especially, the bus is not excited and thus the cavity decay is suppressed during the implementation of DJ algorithm. For the QPG operation, the mode of the bus is unchanged in the end of the operation, although its mode is really excited during the operations. Finally, for typical experiment data, we analyze simply the experimental feasibility of the proposed scheme. Based on the simple operation, our scheme may be realized in this solid-state system, and our idea may be realized in other systems.     

A high-fidelity memory scheme for quantum data buses

A novel quantum memory scheme is proposed for quantum data buses in scalable quantum computers by using adjustable interaction. Our investigation focuses on a hybrid quantum system including coupled flux qubits and a nitrogen–vacancy center ensemble. In our scheme, the transmission and storage(retrieval) of quantum state are performed in two separated steps, which can be controlled by adjusting the coupling strength between the computing unit and the quantum memory. The scheme can be used not only to reduce the time of quantum state transmission, but also to increase the robustness of the system with respect to detuning caused by magnetic noises. In comparison with the previous memory scheme, about 80% of the transmission time is saved. Moreover, it is exemplified that in our scheme the fidelity could achieve 0.99 even when there exists detuning, while the one in the previous scheme is 0.75.     

在热腔中产生多原子GHZ态的方法

我们提出了一个在热腔中产生多原子GHZ态的方法来检验量子非定域性。在这个方法中,三个原子被同时送入一个热腔中,它们初始时处于相同的态。这个方法既对腔的衰减不敏感又对热场不敏感,这为检验量子力学的基本方面提供了新的前景。     

稳定的低噪声自由空间量子密钥分配实验研究

基于量子密钥分配的基本原理,采用偏振短脉冲相干光源和双FM差分密钥分配的方案,进行了自由空间量子密钥分配的实验研究. 该方案具有噪声低,稳定性高,误码率低等优点,为空间量子保密通信提供了一个有意义的实施方案,具有一定的实用价值和学术意义. 关键词： 量子保密通信 量子密钥 自由空间 差分相位编码     

热囚禁离子系统中的两量子比特条件相位门的简单方案

提出了一个实现两离子量子逻辑门的简单方案。本方案使用了两个囚禁于线性阱的三能级离子。本方案不使用振动模作为数据总线,仅需要激光与离子的单个相互作用,因而相互作用时间变短,这点从退相干的角度看是很重要的,而且本方案对振动模的加热不敏感。     

Multiphonon-resonance quantum Rabi model and adiabatic passage in a cavity-optomechanical system

In this paper,we propose a scheme to achieve a multiphonon-resonance quantum Rabi model and adiabatic passage in a strong-coupling cavity optomechanical system.In the scheme,when the driving bichromatic laser beam is adjusted to the off-resonant j-order red-and blue-sideband,the interaction between the cavity and mechanical oscillator leads to a j-phonon resonance quantum Rabi model.Moreover,we show that there exists a resonant multi-phonon coupling via intermediate states connected by counter-rotating processes when the frequency of the simulated bosonic mode is near a fraction of the transition frequency of the simulated two-level system.As a typical example,we theoretically analyze the two-phonon resonance quantum Rabi model,and derive an effective Hamiltonian of the six-phonon coupling.Finally,we present a method of six-phonon generation based on adiabatic passage across the resonance.Numerical simulations confirm the validity of the proposed scheme.Theoretically,the proposed scheme can be extended to the realization of 3j-phonon state.     

Quantum search via superconducting quantum interference devices in a cavity

We propose a scheme for implementing the Grover search algorithm with two superconducting quantum interference devices (SQUIDs) in a cavity. Our scheme only requires single resonant interaction of the SQUID-cavity system and the required interaction time is very short. The simplicity of the process and the reduction of the interaction time are important for restraining decoherence.     

基于六光子量子避错码的量子密钥分发方案

量子信道中不可避免存在的噪声将扭曲被传输的信息,对通信造成危害。目前克服量子信道噪声的较好方案是量子避错码（QEAC）。将量子避错码思想用于量子密钥分发,能有效克服信道中的噪声,且无需复杂的系统。用六光子构造了量子避错码,提出了一种丛于六光子避错码的量子密钥分发（QDK）方案。以提高量子密钥分发的量子比特效率和安全性为前提,对六光子避错码的所有可能态进行组合,得到一种六光子避错码的最优组合方法,可将两比特信息编码在一个态中,根据测肇结果和分组信息进行解码,得到正确信息的平均概率为7／16。与最近的基于四光子避错码的克服量子信道噪声的量子密钥分发方案相比,该方案的量子比特效率提高了16．67％,密钥分发安全性足它的3．5倍。     

Quantum Information Transfer from a Double Quantum Dot System to a Cavity Field＊

In this paper, we propose a scheme to realize quantum information transfer from a double quantum dot （DQD） system to a quantized cavity field. The DQD and the cavity field are treated as a two-state charge qubit and a continuous-variable system, respectively. It is shown that quantum information encoded in the two-state DQD system can be transferred to quantum states of the cavity field with a continuous-variable basis through appropriate projective measurements with respect to the DQD.     

Nonlocal quantum cloning via quantum dots trapped in distant cavities

A scheme for implementing nonlocal quantum cloning via quantum dots trapped in cavities is proposed.By modulating the parameters of the system,the optimal 1 → 2 universal quantum cloning machine,1 → 2 phase-covariant cloning machine,and 1 → 3 economical phase-covariant cloning machine are constructed.The present scheme,which is attainable with current technology,saves two qubits compared with previous cloning machines.     

A simple scheme for implementing four-atom quantum dense coding in cavity QED

An experimentally feasible scheme for implementing four-atom quantum dense coding of an atom--cavity system is proposed. The cavity is only virtually excited and no quantum information will be transferred from the atoms to the cavity. Thus the scheme is insensitive to cavity decay and the thermal field. In the scheme, Alice can send faithfully 4 bits of classical information to Bob by sending two qubits. Generalized Bell states can be exactly distinguished by detecting the atomic state, and quantum dense coding can be realized in a simple way.     

一种新的单光源多波长双向量子密钥分发系统

针对"即插即用"双向量子密钥分发系统传输效率低的实际问题, 详细分析了系统低效的原因和当前的解决方案, 提出了一种单光源多波长双向量子密钥分发方案. 该方案采用波分复用器件作为滤波器来产生量子密钥分发所需的多波长信号. 与其他多波长方案相比, 该方案的优点是在实现高速多波长量子密钥分发时, 不再受外界控制源调制速率和精度等性能的影响, 不再带来多激光器引入的边信道攻击的缺陷, 且整体系统易于集成. 该方案为"即插即用"量子密钥分发系统的高效研究提供了一个新的参考方案.     

运行双协议相位调制的量子密钥分发系统

基于差分编码方式提出一种改进方案.在Alice端用光纤马赫-曾德干涉仪产生双脉冲差分信号；在Bob端，用双法拉第反射式麦克尔逊干涉仪代替光纤马赫-曾德干涉仪，这种干涉仪能自动补偿环境引起的偏振抖动和光纤双折射引起的相位漂移，从而提高系统稳定性.双协议(即双脉冲差分协议联合BB84协议)的使用，增强了系统的安全性.该系统具有高效、安全、简洁、稳定等优点，在实验上实现了长期稳定的密钥分发和量子保密通信，误码率<5%，传输距离达80km.     

Birkhoffian Symplectic Scheme for a Quantum System

In this paper, a classical system of ordinary differential equations is built to describe a kind of n-dimensional quantum systems. The absorption spectrum and the density of the states for the system are defined from the points of quantum view and classical view. From the Birkhoffian form of the equations, a Birkhoffian symplectic scheme is derived for solving n-dimensional equations by using the generating function method. Besides the Birkhoffian structure- preserving, the new scheme is proven to preserve the discrete local energy conservation law of the system with zero vector f . Some numerical experiments for a 3-dimensional example show that the new scheme can simulate the general Birkhoffian system better than the implicit midpoint scheme, which is well known to be symplectic scheme for Hamiltonian system.     

An Alternative Scheme for Transferring Quantum States and Preparing a Quantum Network in Cavity QED

An alternative scheme is proposed to transfer quantum states and prepare a quantum network in cavity QED. It is based on the interaction of a two-mode cavity field with a three-level V-type atom. In the scheme, the atom-cavity field interaction is resonant, thus the time required to complete the quantum state transfer process is greatly shortened, which is very important in view of decoherence. Moreover, the present scheme does not require one mode of the cavities to be initially prepared in one-photon state, thus it is more experimentally feasible than the previous ones.     

Unconventional Geometric Phase Gate with Superconducting Quantum Interference Device Qubits in Cavity QED

In the system with superconducting quantum interference devices （SQUID） in cavity, a scheme for constructing two-qubit quantum phase gate via a conventional geometric phase-shift is proposed by using a quantized cavity field and classical microwave pulses. In this scheme, the gate operation is realized in the subspace spanned by the two lower flux states of the SQUID system mud the population operator of the excited state has no effect on it. Thus the effect of decoherence caused from the levels of the SQUID system is possible to minimize. Under cavity decay, our strictly numerical simulation shows that it is also possible to realize the unconventional geometric phase gate. The experimental feasibility is discussed in detail.     

Implementation of a multiple round quantum dense coding using nuclear magnetic resonance

~~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…