两分量玻色-爱因斯坦凝聚系统的自旋压缩

在周期性脉冲撞击的两分量玻色－爱因斯坦凝聚系统中研究了自旋压缩动力学性质,结果表明：原子自旋压缩动力学能够揭示相空间的混沌和规则结构,即当初始相干态处在混沌区域时,自旋压缩在很短时间后消失,而当初始相干态处在规则区域时,自旋压缩则存在很长时间.特别是随着时间的演化,系统的平均自旋方向的分布和摆动也与初态所处的空间结构有着密切的联系.最后,研究了相空间的整体自旋压缩动力学,得到了一种较好的量子-经典对应. 关键词： 玻色-爱因斯坦凝聚 混沌 自旋压缩 平均自旋方向     

Dicke模型的量子经典对应关系

非旋波近似条件下Dicke模型表现为量子混沌动力学特征.在详细考察Dicke模型经典相空间结构特点的基础上,采用经典-量子"一对多"的思想,即经典相空间中的一点对应于量子体系两个初始相干态的演化,利用对两个初态量子纠缠动力学演化取统计平均的方法,得到了与经典相空间对应非常好的量子相空间结构.数值计算结果表明:经典混沌有利地促进系统两体纠缠的产生,平均纠缠可以作为量子混沌的标识,利用平均纠缠可以得到一种较好的量子动力学与经典相空间的对应关系. 关键词： Dicke模型 非旋波近似 量子混沌 经典量子对应     

光与物质相互作用系统中的量子Fisher信息和自旋压缩

Fisher信息是估计理论中的重要概念,最近发现与量子信息中的纠缠判据具有密切联系.非旋波近似条件下,Dicke模型经典相空间表现为混沌动力学特征.本文详细考察了Dicke模型描述的光与物质相互作用系统中量子Fisher信息和自旋压缩动力学特性.结果表明:在短时瞬态情况下,无论初态处于规则区域还是混沌区域系统均表现为纠缠性质;但在长时稳态情况下,初态处于规则区域时系统纠缠消失,而初态处于混沌区域时系统则一直存在纠缠.通过与系统自旋压缩动力学性质相比较,发现量子Fisher信息可以更有效地刻画量子混沌.进一步考察初态处于规则和混沌区域时系统密度矩阵和纯度的动力学演化特性,发现混沌导致系统退相干现象发生,说明量子Fisher信息对混沌更敏感.     

玻色-爱因斯坦凝聚系统的量子Fisher信息与混沌

量子Fisher信息作为经典Fisher信息的自然推广,与量子信息中的纠缠判断具有密切联系.在表现为典型量子混沌特征的受击两分量玻色-爱因斯坦凝聚系统中,研究了与经典相空间对应的纠缠和量子Fisher信息动力学性质. 结果表明,初次撞击后的系统量子态是纠缠的,与初态所处相空间中的混乱程度无关.而量子Fisher信息的动力学演化对系统初态非常敏感,当初态处于混沌区域时,量子Fisher信息值比初态处于规则区域时大.利用这种较好的量子-经典对应关系,得到量子Fisher信息可以刻画量子混沌的结论. 关键词： 量子Fisher信息 玻色-爱因斯坦凝聚 量子混沌 量子-经典对应     

Dicke模型的量子混沌和单粒子相干动力学特性

量子化的Dicke模型在非旋波近似条件下表现为量子混沌动力学特征.利用单粒子一阶时间关联函数,通过数值计算详细考察了Dicke模型中单粒子相干动力学特性.结果表明:当初始相干态处在混沌区域时,一阶时间关联函数曲线衰减较快,而当初始相干态处在规则区域时,一阶时间关联函数曲线衰减较慢,单粒子相干动力学对初态具有较强的敏感性,经典混沌抑制量子相干.考察单粒子相干动力学在相空间的平均演化性质,得到一种较好的量子经典对应关系.最后研究了相空间单粒子相干的整体动力学性质,更好地揭示了相空间的混沌和规则结构.     

Entanglement Swapping of Pair Coherent States with Phase Decoherence

We investigate the entanglement swapping of continuous state and the two-mode squeezed vacuum which is exposed variable using the pair coherent state as the input in a phase decoherence environment as the quantum channel. By adopting the log-negativity as the measure of entanglement, we analyze how entanglement of the two initial states and the phase decoherence environment affect the entanglement swapping quality.     

Linear entropy in the Jaynes-Cummings model with a Kerr nonlinearity

The dynamical properties of quantum entanglement in the integrable Jaynes-Cummings model with a Kerr nonlinearity are studied in terms of the reduced-density linear entropy with various Kerr coupling parameters and initial states, where the initial states are prepared by the coherent states placed in the corresponding phase space described in terms of canonical variables. The mean entanglement averaged over time is employed to investigate the behavior of entanglement of those coherent states. It is shown that the mean entanglement of the coherent states put near the centers of periodic orbits, both with a strong Kerr coupling and without a Kerr coupling, tends to be the minimal, and that the mean entanglement of the coherent states centered near the boundary with a strong Kerr coupling is the minimal while that without Kerr coupling is the maximal.     

Chaotic Entanglement: Entropy and Geometry

In chaotic entanglement, pairs of interacting classically-chaotic systems are induced into a state of mutual stabilization that can be maintained without external controls and that exhibits several properties consistent with quantum entanglement. In such a state, the chaotic behavior of each system is stabilized onto one of the system’s many unstable periodic orbits (generally located densely on the associated attractor), and the ensuing periodicity of each system is sustained by the symbolic dynamics of its partner system, and vice versa. Notably, chaotic entanglement is an entropy-reversing event: the entropy of each member of an entangled pair decreases to zero when each system collapses onto a given period orbit. In this paper, we discuss the role that entropy plays in chaotic entanglement. We also describe the geometry that arises when pairs of entangled chaotic systems organize into coherent structures that range in complexity from simple tripartite lattices to more involved patterns. We conclude with a discussion of future research directions.     

Entanglement and localization of a two-mode Bose-Einstein condensate

A simple second quantization model is used to describe a two-mode Bose-Einstein condensate (BEC), which can be written in terms of the generators of a SU(2) algebra with three parameters. We study the behavior of the entanglement entropy and localization of the system in the parameter space of the model. The phase transitions in the parameter space are determined by means of the coherent state formalism and the catastrophe theory, which besides let us get the best variational state that reproduces the ground state energy. This semiclassical method let us organize the energy spectrum in regions where there are crossings and anticrossings. The ground state of the two-mode BEC, depending on the values of the interaction strengths, is dominated by a single Dicke state, a spin collective coherent state, or a superposition of two spin collective coherent states. The entanglement entropy is determined for two recently proposed partitions of the two-mode BEC that are called separation by boxes and separation by modes of the atoms. The entanglement entropy in the boxes partition is strongly correlated to the properties of localization in phase space of the model, which is given by the evaluation of the second moment of the Husimi function. To compare the fitness of the trial wavefunction its overlap with the exact quantum solution is evaluated. The entanglement entropy for both partitions, the overlap and localization properties of the system get singular values along the separatrix of the two-mode BEC, which indicates the phase transitions which remain in the thermodynamical limit, in the parameter space.     

相空间中对称的纠缠相干态及其非经典特性

研究相空间中对称的纠缠相干态, 通过引入正交基矢, 利用concurrence方法计算了纠缠度, 研究了它们的单、双模压缩以及反聚束效应. 数值计算表明, 相空间中对称的纠缠相干态与非经典效应之间存在着密切的联系. 关键词： 纠缠相干态 concurrence 非经典效应     

Relative phase based manipulation of quantum entanglement and measurement of supercurrent

We investigate the quantum entanglement and supercurrent of coupling superconducting qubits in circuit QED system. We compare the effect of the relative phase of the coupling qubits on the concurrence and supercurrent when the microwave field is initially in coherent state, even coherent state and odd coherent state. The results show that entanglement death can be avoided via manipulating the relative phase only in the coherent state since the improvement for entanglement death is unsatisfactory in the even coherent state and odd coherent state.     

Chaotic oscillations associated with the breakup of polarization entangled coherent states in a microchip solid-state laser

We demonstrate the breakup of spatial-polarization entangled lasing patterns, which possess vector phase singularities, and the resultant dynamic instabilities featuring chaotic oscillations. The frequency splitting between a pair of Ince-Gauss (IG) lasing modes, originally forming a coherent entanglement state, and a self-excited additional nonorthogonal IG mode through a new class of transverse effect of self-injection pattern seeding, is shown to result in modal-interference-induced modulation at the beat frequency, leading to chaotic oscillations.     

Combined Effect of Classical Chaos and Quantum Resonance on Entanglement Dynamics

We use linear entropy of an exact quantum state to study the entanglement between internal electronic states and external motional states for a two-level atom held in an amplitude-modulated and tilted optical lattice.Starting from an unentangled initial state associated with the regular 'island' of classical phase space,it is demonstrated that the quantum resonance leads to entanglement generation,the chaotic parameter region results in the increase of the generation speed,and the symmetries of the initial probability distribution determine the final degree of entanglement.The entangled initial states are associated with the classical 'chaotic sea',which do not affect the final entanglement degree for the same initial symmetry.The results may be useful in engineering quantum dynamics for quantum information processing.     

Nonclassical state via superposition of two coherent states (π/2 out of phase) and related entangled states

Nonclassical features of the superposition of two coherent states which are π/2 out of phase are discussed, such as sub-Poissonian photon statistics and quadrature squeezing, as well as negativity of the Wigner function. Special nonclassicality is found in the special state where the relative phase of superposition has relationship with the average photon number. The analysis of the amount of entanglement is also presented for the related two-mode entangled coherent states.     

Entanglement and nonclassicality evolution of the atom in a squeezed vacuum

As an important parameter, von Neumann entropy has been used to characterize the entanglement between atom and light field. We discussed the entanglement and nonclassicality evolution of an atom in a squeezed vacuum—a typical nonclassical field, and compare it with that of the coherent state. It shows that the atom-field entanglement in squeezed vacuum is much stronger and stabler than that in coherent state, whereas the nonclassicality of the light field depends on its initial status. This investigation is trying to find a new insight into the relation between entanglement of atom-field system and nonclassicality of light fields. The result shows that the entanglement between the atom and the field can be maintained well in the squeezed vacuum and this implies better control of atom and photon mutually.     

Multipartite Entanglement Transfer from Multi-Mode Coherent State to Spin Qubits

The multipartite entanglement transfer from continuous variable system to spin qubits is investigated. We select multi-mode coherent field as continuous variable field. It is found that the qubits can not gain tripartite entanglement for states of close to GHZ state from the multi-mode coherent field. Moreover, the ability of the qubits gain the tripartite entanglement for states close to W state and bipartite entanglement from the continuous variable system is depended on the phase of multi-mode coherent field.     

Entropy evolvement properties in a system of Schrodinger cat state light field interacting with two entangled atoms

The field entropy can be regarded as a measurement of the degree of entanglement between the light field and the atoms of a system which is composed of two-level atoms initially in an entangled state interacting with the Schr\"{o}dinger cat state. The influences of the strength of light field and the phase angle between the two coherent states on the field entropy are discussed by using numerical calculations. The result shows that when the strength of light field is large enough the field entropy is not zero and the degrees of entanglement between the atoms and the three different states of the light fields are equal. When the strength of the light field is small, the degree of entanglement is maximum in a system of the two entangled atoms interacting with an odd coherent state; it is intermediate for a system of the two entangled atoms interacting with the Yurke--Stoler coherent state, and it is minimum in a system of the two entangled atoms interacting with an even coherent state.     

Engineering Two-Mode Non-Gaussian States with Vortex Structures Using a Beam Splitter

Vortex structure and entanglement properties of output field from a beam splitter are investigated. With a n-photon Fock state and a coherent state as the inputs, it is found that the output state before a beam splitter bears a vortex structure in quadrature space and is always entangled and non-classical based on the linear entropy criterion and the P-function analysis in phase space.     

Schwinger Bose实现下自旋相干态Wigner函数的特性分析

在Schwinger Bose实现下,引入纠缠态表象及Wigner算符在该表象下的表示,得到自旋相干态的Wigner函数,数值计算画出相空间中Wigner函数的分布图,并加以分析,发现在SchwingerBose实现下自旋相干态确实体现出纠缠特性。     

Entanglement of three-level trapped ions with phonon trap modes

The entanglement between a single electron in the electronic states of a trapped three-level ion and the ionic vibrational modes of the trap is studied for an initially unentangled state of an electron level and a coherent phonon state. The effects of time-independent and time-dependent couplings are discussed.