Generation of a χ-type four-atom entangled state

This paper proposes a scheme to generate a new χ-type four-atom entangled state for the first time by using linear optics elements, four one-sided cavities (one three-level atom) and a conventional photon detector. The linear optical elements and conventional photon detector are simple and accessible in experiments, which makes the scheme more feasible with current technology. In addition, the state |χ⁰⁰₃₂₁₄ with probability 1 can be generated as long as there is no photon loss.     

The influences of dipole--dipole interaction and detuning on the sudden death of entanglement between two atoms in the Tavis--Cummings model

The influences of dipole--dipole interaction and detuning on the entanglement between two atoms with different initial tripartite entangled W-like states in the Tavis--Cummings model have been investigated by means of Wootters' concurrence, respectively. The results show that the entanglement between the two atoms can be enhanced via appropriately tuning the strength of dipole--dipole interaction of two atoms or the detunings between atom and cavity, and the so-called sudden death effect can be weakened simultaneously.     

与非等同双原子相互作用下光场的量子特性

研究了具有不同偶极矩的两个原子与双模压缩真空场相互作用系统中光场的量子特性.讨论了两个原子与双模压缩真空场的相对耦合常数(R=g1/g2)和光场的初始压缩因子r对光场的压缩效应和光子的聚束与反聚束效应的影响.数值计算结果表明,光场量子涨落的震荡幅度、最大压缩深度、压缩时间及二阶相干度的震荡振幅与光场的初始压缩因子r的大小有关.两原子与双模光场的相对耦合常数R影响着光场量子涨落和二阶相干度的震荡规律,因而也影响着压缩时间、光场处于非经典态的时间及光子的反聚束程度,但对光场的压缩深度无明显影响.     

腔QED中相位协变量子克隆机的实现及纠错

应用N个二能级原子和单模真空腔场相互作用,提出了一个1→2的相位协变量子克隆机的方案.同时,基于这种克隆机,我们也提出了量子纠错方案,考虑了由相位和比特反转错误所产生的消相干影响,通过对后两个比特位进行Bell测量,并沿着合适的轴旋转第一比特,就可以恢复初始态.     

Quantum Logic Network for Cloning a State Near a Given One Based on Cavity QED

A quantum logic network is constructed to simulate a cloning machine which copies states near a given one. Meanwhile, a scheme for implementing this cloning network based on the technique of cavity quantum electrodynamics （QED） is presented. It is easy to implement this network of cloning machine in the framework of cavity QED and feasible in the experiment.     

Complete hyperentangled state analysis and generation of multi-particle entanglement based on charge detection

We propose the schemes for implementing hyperentangled state analysis and generating four-electron high entan-gled states （including cluster state, ｜X） state, and symmetric Dicke state） based on the charge detection of free electrons. These schemes are deterministic and rely only on charge detection and single-spin rotations. This method, which uses noninteracting electrons, is not only efficient but also saves on quantum resources.     

Secret sharing of quantum information via entanglement swapping

Based on entanglement swapping, a scheme for the secret sharing of an arbitrary two-particle entangled state is proposed. If the controllers do not co-operate with the eavesdropper, the eavesdropper's successful probability decreases with the number of the controllers increasing. In addition, only the Bell-state measurements are required to realize the secret sharing scheme.     

Two simple schemes for implementing Toffoli gate via atom--cavity field interaction in cavity quantum electrodynamics

This paper proposes two schemes for implementing three-qubit Toffoli gate with an atom (as target qubit) sent through a two-mode cavity (as control qubits). The first scheme is based on the large-detuning atom--cavity field interaction and the second scheme is based on the resonant atom-field interaction. Both the situations with and without cavity decay and atomic spontaneous emission are considered. The advantages and the experimental feasibility of these two schemes are discussed.     

One-step implementing three-qubit phase gate via manipulating rf SQUID qubits in the decoherence-free subspace with respect to cavity decay

We present a scheme for implementing a three-qubit phase gate via manipulating rf superconducting quantum interference device (SQUID) qubits in the decoherence-free subspace with respect to cavity decay. Through appropriate changes of the coupling constants between rf SQUIDs and cavity, the scheme can be realized only in one step. A high fidelity is obtained even in the presence of decoherence.     

Generation of arbitrary four-atom entangled decoherence-free states

This paper proposes a scheme to generate arbitrary four-atom entangled decoherence-free states by using simple linear optical elements, four one-sided cavities in which four atoms are confined respectively. By conveniently tuning the titled angle of one half-wave plate, it can obtain arbitrary four-atom entangled decoherence-free states with a successful probability of 1 as long as there is no photon loss.