Entropy squeezing for a two-level atom in the Jaynes－Cummings model with an intensity-depend coupling

We study the squeezing for a two-level atom in the Jaynes－Cummings model with intensity-dependent coupling using quantum information entropy, and examine the influences of the initial state of the system on the squeezed component number and direction of the information entropy squeezing. Our results show that, the squeezed component number depends on the atomic initial distribution angle, while the squeezed direction is determined by both the phases of the atom and the field for the information entropy squeezing. Quantum information entropy is shown to be a remarkable precision measure for atomic squeezing.     

Preparation of arbitrary n-particle d-dimensional superposition states using only single qubit operations and CNOT gates

In this article, using only single qubit operation and a CNOT gate, we propose a scheme for creating arbitrary n-particle d-dimensional superposition states including entangled states and give the relevant circuits for realizing this scheme.     

Sudden death and revival qubits coupled collectively of entanglement of two to a thermal reservoir

In this paper, we investigate the entanglement of two qubits coupled collectively to a common thermal environment and find that the the collective decay can lead to a revival of the entanglement that has already been destroyed. We also show that the ability of the system to revival entanglement relies on the mean photon number of the thermal environment and the degree of entanglement of the initial state.     

Protection of entanglement between two V-atoms in a multi-cavity coupling system

The protection of the entanglement between two V-atoms(EBTVA)in a multi-cavity coupling system is studied.The whole system consists of two V-atoms.The two V-atoms are initially in the maximum entangled state and interacts locally with its own dissipative cavity which is coupled to the external cavities with high quality factor(ECWHQF).The results show that,when there is no ECWHQF,the EBTVA can be protected effectively in the case where the V-atom and the dissipative cavity are weak coupled in large detuning,while when there are different numbers n of ECWHQF coupled to two dissipative cavities,by adjusting the parameters of the number n of ECWHQF and the coupling strength k between cavities,the EBTVA can be protected perfectly and continuously.Our result provides an effective method for protecting entanglement resources of three-level system.     

Distributed quantum computation with superconducting qubit via LC circuit using dressed states

A scheme is proposed where two superconducting qubits driven by a classical field interacting separately with two distant LC circuits connected by another LC circuit through mutual inductance,are used for implementing quantum gates.By using dressed states,quantum state transfer and quantum entangling gate can be implemented.With the help of the time-dependent electromagnetic field,any two dressed qubits can be selectively coupled to the data bus (the last LC circuit),then quantum state can be transferred from one dressed qubit to another and multi-mode entangled state can also be formed.As a result,the promising perspectives for quantum information processing of mesoscopic superconducting qubits are obtained and the distributed and scalable quantum computation can be implemented in this scheme.     

Generation of Wn state with three atoms trapped in two remote cavities coupled by an optical fibre

We propose two schemes for the generation of the Wn state with three atoms separately trapped in two distant cavities coupled by an optical fibre.One is implemented by controlling the interaction time,the other is implemented via the adiabatic passage.The influence of various decoherence processes,such as spontaneous emission of the atoms and photon leakages of the cavities and the optical fibre,on the fidelity is also investigated.It is found that the Wn state can be generated with high fidelity even when these decoherence processes are present.     

压缩相干态通过参量图像放大系统的光学像

取压缩相干态作为参量图像放大系统的输入像，研究了输出光学像的性质.结果表明：参量 图像放大系统能够控制输出光学像的压缩度和压缩方向，即压缩度的增加与减小和压缩方向 的改变决定于参量图像放大系统的参数选择. 关键词： 参量图像放大系统 压缩相干态 压缩度 压缩方向角     

Controlling the entropic uncertainty and quantum discord in two two-level systems by an ancilla in dissipative environments

The uncertainty principle is a crucial aspect of quantum mechanics.It has been shown that the uncertainty principle can be tightened by quantum discord and classical correlation in the presence of quantum memory.We investigate the control of the entropic uncertainty and quantum discord in two two-level systems by an ancilla in dissipative environment.Our results show that the entropic uncertainty of an observed system can be reduced and the quantum discord between the observed system and the quantum memory system can be enhanced in the steady state of the system by adding an dissipative ancilla.Particularly,via preparing the state of the system to the highest excited state with hight fidelity,the entropic uncertainty can be reduced markedly and the quantum discord can be enhanced obviously.We explain these results using the definition of state fidelity.Furthermore,we present an effective strategy to further reduce the the entropic uncertainty and to enhance the the quantum discord via quantum-jump-based feedback control.Therefore,our results may be of importance in the context of quantum information technologies.     

Efficient scheme for teleportation of an unknown N-atom state via a two-atom entangled state without the Bell-state measurement in cavity QED

We propose a scheme for teleportation of an unknown N-atom state using a two-atom entangled state within a cavity QED and show the feasibility in experiment. Our scheme does not involve the Bell-state measurement and is insensitive to the cavity decay, which is important from the experimental point of view. Another feature of the scheme is that teleporting a N-atom state just requires a small amount of entanglement （i,e. a two-atom entangled state） and less classical bits （two bits）.     

Quantum Correlation without Entanglement in a Two-Atom-Vacuum Field System

Quantum correlation without entanglement in a two-atom-vacuum field system is investigated. The influence of the atomic dipole-dipole interaction on quantum correlation is also examined. We find that, when both atoms are initially in separable excited states, the quantum discord of two atoms appears while their entanglement wholly vanishes throughout the evolution. We explain our results in detail Our results provide a novel method of achieving a quantum correlation resource without entanglement in the real system.