Continuous-variable Entanglement in a Correlated Spontaneous Emission Laser

We discuss the generation and evolution of entangled light in a correlated spontaneous emission laser in the linear regime. The master equation for the two-mode cavity field is derived and solved analytically in phase space. The time-dependent characteristic function in the Wigner representation for the two-mode field is obtained. It shows that the two-mode field in the cavity evolves in a two-mode Gaussian state. The entanglement degree of the two- mode field in the cavity increases initially, then decreases, and finally vanishes as the field evolves from an initial vacuum. The period of the entanglement is extended as the intensity of the driving field is increased. It is found that the entanglement still exists even when the two-mode squeezing disappears. During the entanglement period, the intensity of the field is amplified. The entanglement for the initial field being a two-mode squeezed vacuum and the entanglement of the output field are also discussed.     

Correlated Emission Laser as an Entanglement Amplifier

We consider a two-photon correlated emission laser as a source of an entangled radiation with a large number of photons in each mode. The system consists of three-level atomic schemes inside a doubly resonant cavity. We study the dynamics of this system in the presence of cavity losses, concluding that the creation of entangled states with photon numbers up to tens of thousands seems achievable.     

Bipartite and Tripartite Entanglement in a Three-Qubit Heisenberg Model

The bipartite and tripartite entanglement in a three-qubit Heisenberg XY model with a nonuniform magnetic field is studied. There are two or four peaks in the concurrence of the bipartite entanglement when the amplitudes of the magnetic fields are. differently distributed between the three qubits. It is very interesting to note that there is no tangle of tripartite entanglement between the three qubits when the amplitudes of the magnetic fieMs are varied. However, the variation of the magnetic field direction can induce the tangle. The tangle is periodic about the angle between the magnetic field and the z axis of the spin.     

Bipartite and Tripartite Entanglement in a Three-Qubit Heisenberg Model

The bipartite and tripartite entanglement in a three-qubit Heisenberg XY model with a nonuniformmagnetic field is studied. There are two or four peaks in the concurrence of the bipartite entanglement when the amplitudes of the magnetic fields are differently distributed between the three qubits. It is very interesting to note that there is no tangle of tripartite entanglement between the three qubits when the amplitudes of the magnetic fields are varied. However, the variation of the magnetic field direction can induce the tangle. The tangle is periodic about the angle between the magnetic field and the z axis of the spin.     

Entanglement in Bipartite Generalized Coherent States

Entanglement of formation in a class of bipartite generalized coherent states is discussed. It is shown that a positive parameter can be associated with these bipartite states so that the states with equal value for the parameter are of equal entanglement. For the class of states considered, the maximum possible entanglement of one ebit is attained if the value of the positive parameter is . It is shown that the entanglement of formation is one ebit when the relative phase between the composing states is π in the class of bipartite generalized coherent states considered.     

一类两体三参量态的量子纠缠特性

讨论了一类三参量量子态的纠缠特性.计算了2(×)n量子系统该类态的concurrence,讨论了其形成纠缠度的下限.并计算了m(×)n量子系统(2≤m≤n)该类态的负值度,得到了解析表达式.研究表明参量θ=π/4时,该类量子态的纠缠达到最大值,并归结为已有文献研究的一类二参量量子态.对于2(×)n量子系统三参量量子态,其concurrence等于负值度,所有的PPT态都是可分离的,所有的NPT态都是纠缠的.对于高维情形,三参量态就没有类似的结论.     

Bipartite Entanglement in the Two-Mode Quantum Kicked Top

We show that the bipartite entanglement in the two-mode quantum kicked top can reveal the underlying chaotic and regular structures in phase space： namely, the entanglement displays a rapid rise after a very short time for an initial spin coherent state centred in a chaotic region of the phase space, whereas the entanglement displays a periodic modulation for the coherent state centred at an elliptic fixed point. The quantum-classical correspondence is investigated by studying the mean and maximal linear entropy.     

Classification of Bipartite and Tripartite Qutrit Entanglement Under SLOCC

We classify biqutrit and triqutrit pure states under stochastic local operations and classical communication. By investigating the right singular vector spaces of the coefticient matrices of the states, we obtain explicitly two equivalent classes of biqutrit states and twelve equivalent classes of triqutrit states respectively.     

Classification of Bipartite and Tripartite Qutrit Entanglement Under SLOCC

We classify biqutrit and triqutrit pure states under stochastic local operations and classical communication. By investigating the right singular vector spaces of the coefficient matrices of the states, we obtain explicitly two equivalent classes of biqutrit states and twelve equivalent classes of triqutrit states respectively.     

Trade-off between Squashed Entanglement and Concurrence in Bipartite Quantum States

International Journal of Theoretical Physics - In this article, we investigate the unitary dynamics of squashed entanglement and concurrence measures in Werner state and maximally entangled mixed...     

Bipartite Entanglement Dynamics in Three Qubits System withDzyaloshinskii-Moriya Interaction

We investigate the bipartite entanglement dynamics of the systemcomposed by three qubits A, B, and C. There is no interaction betweenA and B, and that of C and B is Dzyaloshinskii-Moriya (DM) spin-orbit interaction. We find that the purity of qubits A and B and the initial state of the qubit C are the two effective parameters to control the entanglement dynamics of the bipartite subsystems. This study sheds some lights on the control of quantum entanglement, which would be helpful for quantum information processing.     

Simple Procedure for Entanglement Transformation of Bipartite Pure States

An explicit procedure for transforming one bipartite entangled state into another via local operations and classical communication （LOCC） is presented. Our procedure is much simper than the previous ones in the sense that, it only involves two steps and the explicit expression of local general measurement used in the procedure can be obtained by solving a set of linear equations. Furthermore, this procedure is still applicable in high dimensional case.     

Degree of Entanglement for Some Bipartite Entangled Bosonic Systems

We calculate the degree of entanglement for some bipartite entangled states of continuous variables.These states include common two-mode squeezed vacuum state, thermal vacuum state of a free single particle (where theh fictitious tilde system is regarded as another particle), and the squeezed vacuum state of two coupling harmonic oscillators.The degree of entanglement for these quantum systems are shown clearly by using the technique of integration within an ordered product of operators.     

Degree of Entanglement for Some Bipartite Entangled Bosonic Systems

We calculate the degree of entanglement for some bipartite entangled states of continuous variables.These states include common two-mode squeezed vacuum state, thermal vacuum state of a free single particle (where the fictitious tilde system is regarded as another particle), and the squeezed vacuum state of two coupling harmonic oscillators.The degree of entanglement for these quantum systems are shown clearly by using the technique of integration within an ordered product of operators.     

Bipartite Entanglement Dynamics in Three Qubits System with Dzyaloshinskii-Moriya Interaction

We investigate the bipartite entanglement dynamics of the system composed by three qubits A, B, and C. There is no interaction between A and B, and that of C and B is Dzyaloshinskii-Moriya （DM） spin-orbit interaction. We find that the purity of qubits A and B and the initial state of the qubit C are the two effective parameters to control the entanglement dynamics of the bipartite subsystems. This study sheds some lights on the control of quantum entanglement, which would be helpful for quantum information processing.