Single-Particle Coherence and Spin Squeezing in Four-Qubit Phase State

We investigate single-particle coherence and spin squeezing in four-qubit phase state governed by an one-axis twisting Hamiltonian. In particular, we are interesting in the dependence of single-particle coherence and spin squeezing on the nonlinear interaction. It is shown that single-particle coherence and spin squeezing parameter only depend on the nonlinear interaction and they are periodic function of nonlinear interaction.     

Single-Particle Coherence and Spin Squeezing in Two-Particle Phase State

We investigate the relation between the single-particle coherence and spin squeezing in two-particle phase state governed by an one-axis twisting Hamiltonian. The single-particle coherence and spin squeezing parameter only depends on the nonlinear interaction, and they have the same period of oscillation and the maximum and the minimum.     

Quantum Coherence and Spin Squeezing in Bose-Einstein Condensate with Josephson-Like Coupling

We consider single-particle coherence and spin squeezing in Bose-Einstein Condensate (BEC) with Josephson-like coupling when the BEC is initially in a coherent spin state. Josephson-like coupling gives vanishing contribution to single-particle coherence and spin squeezing. The stronger squeezing can be achieved by increasing the number of atoms.     

Phase Coherence and Spin Squeezing in One-Axis Twisting Model with Decay

We investigate phase coherence and spin squeezing of a collective spin governed by one-axis twisting Hamiltonian with decay. Here we are interested in the dependence of phase coherence and spin squeezing parameter on the decay. The analytical expressions of phase coherence and spin squeezing parameter are obtained. The stronger decay can induce a stronger spin squeezing, and the squeezing can maintain a longer time interval. Moreover, more squeezing can be achieved by increasing the number of particles.     

Entanglement of Three Atoms Induced by a Coherent Field

We calculate the concurrence and spin squeezing parameter of three atoms induced by a coherent field. It shows that when the mean numbers of photon of the field is very small, concurrence exhibits a certain kind of approximative periodic vibration. With the increase of the mean numbers of photon, its periodicity will be interrupted. As for the relationship between the concurrence and spin squeezing, numeric result shows that under Dick model, spin squeezing serves as a sufficient but not necessary condition for concurrence.     

Entanglement of Three Atoms Induced by a Coherent Field

We calculate the concurrence and spin squeezing parameter of three atoms induced by a coherent field.It shows that when the mean numbers of photon of the field is very small, concurrence exhibits a certain kind of approximative periodic vibration. With the increase of the mean numbers of photon, its periodicity will be interrupted.As for the relationship between the concurrence and spin squeezing, numeric result shows that under Dick model, spin squeezing serves as a sufficient but not necessary condition for concurrence.     

Quantum Coherence and Spin Squeezing in Optomechanical System

We investigate quantum coherence and spin squeezing in optomechanical system. We first determine the mean spin direction, the optimally squeezed angle and then calculate the first-order temporal correlation function, the squeezing parameter, which are independent of the frequency of the cavity field. The lager coupling strength more rapidly generates spin squeezed state, but the corresponding spin squeezed state maintains shorter time interval.     

Spin Squeezing for Superpositions of Dicke States

We investigate spin squeezing for superpositions of Dicke states. We derive the mean spin direction, the length of mean spin, the optimally squeezed angle and numerically calculate the spin squeezing parameter, which is determined by on the superposed coefficients and the relative phase. Approximate same superposed amplitude and the smaller relative phase lead to the larger the length of mean spin, the stronger spin squeezing and spin squeezing maintains in a longer time interval.     

Coherence and Entanglement in Spinor Bose-Einstein Condensate

We propose a scheme to generate and detect quantum coherence and quantum entanglement in a spin-1 Bose-Einstein condensate with the help of spin squeezing parameter and quantum Fisher information. It is shown that quantum coherence and quantum entanglement are independent of the Rabi frequency and the better entanglement can be achieved by increasing the number of atoms.     

非共振双光子Jaynes—Cummings模型中原子的偶极压缩

考虑到失谐量和初始原子相干性，研究了双光子Ｊａｙｎｅｓ－Ｃｕｍｍｉｎｇｓ模型中原子的压缩行为。研究表明，失谐量对场－原子相互作用中的原子压缩行为的影响很大，通过数值计算，还讨论了初始平均光子数与原子压缩的关系。     

非共振双光子Jaynes-Cummings模型中原子的偶极压缩

考虑到失谐量和初始原子相干性，研究了双光子Ｊａｙｎｅｓ－Ｃｕｍｍｉｎｇｓ模型中原子的压缩行为。研究表明，失谐量对场－原子相互作用中的原子压缩行为的影响很大。通过数值计算，还讨论了初始平均光子数与原子压缩的关系。     

Spin Squeezing of a General 3-Qubit State

We investigate the spin squeezing of a general 3-qubit state, which is superposed by a GHZ state and two W states. Numerical solutions for the length of mean spin, mean spin direction and spin squeezing were given. It is shown that the mean spin direction, the length of mean spin and the spin squeezing parameter are determined by the superposition coefficients and the relative phases between the GHZ state and the two W states.     

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.     

Spin Squeezing of Superposition

We investigate the mean spin direction, length of mean spin and spin squeezing in a general superposition of a GHZ state and a W state. It is shown that the mean spin direction and spin squeezing parameter are determined by the coefficients of superposition and the relative phase between the GHZ state and the W state; while the length of mean spin is only determined by coefficients of superposition.     

Controlling Spin Squeezing and Quantum Fisher Information with a Strong External Field

We investigate the mean spin direction, length of mean spin and spin squeezing in a general superposition of a GHZ state and a W state. It is shown that the mean spin direction and spin squeezing parameter are determined by the coefficients of superposition and the relative phase between the GHZ state and the W state; while the length of mean spin is only determined by coefficients of superposition.     

Entangled Property of a Multipartite State Superposed by Three Dicke States with Arbitrary Relative Phases

With spin squeezing parameter we investigate the entangled property of a multipartite state superposed by three Dicke states with arbitrary relative phases. We first derive the mean spin direction, the optimally squeezed angle, and then numerically calculate the dependence of spin squeezing parameter on the superposition coefficients, the relative phases and the forms of the Dicke states. It’s shown that the entangled property depends on these parameters.     

Generating Spin Squeezing State of Two Bose-Einstein Condensates with Josephson-Like Coupling

We propose an experimentally feasible setup for producing dynamically spin squeezing state of two Bose-Einstein Condensates (BECs) with Josephson-like coupling. The spin squeezing parameter is independent of Josephson-like coupling and the stronger squeezing can be achieved by increasing the number of the atoms.     

Coherently Controlling Spin Squeezing in Optomechanical System

We investigate spin squeezing in optomechanical system. We first derive the mean spin direction, the optimally squeezed angle and then calculate the spin squeezing parameter, which is independent of the frequency of the cavity field. The lager coupling strength more rapidly generates spin squeezed state, but the corresponding spin squeezed state maintains shorter time interval.     

Coherence and squeezing in superpositions of spin coherent states

We consider the superpositions of spin coherent states and study the coherence properties and spin squeezing in these states. The spin squeezing is examined using a new version of spectroscopic squeezing criteria. The results show that the antibuching effect can be enhanced and spin squeezing can be generated in the superpositions of two spin coherent states.     

Spin Squeezing and Quantum Fisher Information in Generalized Two-Axis Twisting Model

We investigated spin squeezing and quantum Fisher information in generalized two-axis twisting model; which generalizes the two-axis twisting model including a linear interaction controlled by an external field. In particular, we are interested in the dependence of spin squeezing and quantum Fisher information on the external field. By adopting frozen-spin approximation, we derive the theoretical and numerical results for spin squeezing and quantum Fisher information. Except certain special conditions, the stronger external field induces to stronger squeezing. Spin squeezing parameter and the reciprocal of the mean quantum Fisher information per particle are periodic function; but the external field has not important effect on the period.