双J-C模型中两原子的纠缠动力学特征

初始处于类贝尔纠缠态的完全一样的二能级原子A和B分别与空间分离的两处于真空场的腔场a和腔场b发生相互作用,利用双Jaynes-Cummings理论模型进行分析,我们采用部分转置矩阵的负本征值(negativity)的方法研究了两原子间纠缠度随时间演化的动力学特征,通过数值计算和理论分析发现在一定参数范围内原子间出现纠缠猝死现象;通过参数调整能有效缩小纠缠猝死区域,在一定的参数条件下能有效消除两原子间的纠缠猝死现象。     

Entanglement and coherence of a three-level atom in Λ configuration interacting with two fields

We investigate the entanglement of a three-level atom in λ configuration interacting with two quantized field modes by using logarithmic negativity. Then, we study the relationship of the atomic coherence and the entanglement between two fields which are initially prepared in vacuum or thermal states. We find that if the two fields are prepared in thermal states, the atomic coherence can induce the entanglement between two thermal fields. However, there is no coherence-induced entanglement between two vacuum fields.     

Quantum entanglement in the system of two two-level atoms interacting with a single-mode vacuum field

The entanglement properties of the system of two two-level atoms interacting with a single-mode vacuum field are explored. The quantum entanglement between two two-level atoms and a single-mode vacuum field is investigated by using the quantum reduced entropy; the quantum entanglement between two two-level atoms, and that between a single two-level atom and a single-mode vacuum field are studied in terms of the quantum relative entropy. The influences of the atomic dipole--dipole interaction on the quantum entanglement of the system are also discussed. Our results show that three entangled states of two atoms--field, atom--atom, and atom--field can be prepared via two two-level atoms interacting with a single-mode vacuum field.     

两纠缠原子之一与腔场相互作用过程的纠缠研究

使一对纠缠的二能级原子之一与单模真空腔场发生共振相互作用,通过选择不同的演化时间,对这个三体系统的其中之一做选择性测量,可调节另外两体的纠缠状态。在不做测量时,研究了在不同的初始状态下,三体纠缠及三体中两两纠缠的演化特性。结果表明,该体系纠缠都呈现周期性的振荡,特别是,通过选择合适的初始状态和演化时间可生成强壮纠缠态———W纠缠态;在特定演化时刻,可使两纠缠原子的纠缠信息完全转化到腔外原子和腔场中去。     

Control and Transfer of Entanglement between Two Atoms Driven by Classical Fields under Dressed-State Representation

We have studied the dynamics and transfer of the entanglement of the two identical atoms simultaneously interacting with vacuum field by employing the dressed-state representation. The two atoms are driven by classical fields. The influence of the initial entanglement degree of two atoms, the coupling strength between the atom and the classical field and the detuning between the atomic transition frequency and the frequency of classical field on the entanglement and atomic linear entropy is discussed. The initial entanglement of the two atoms can be transferred into the entanglement between the atom and cavity field when the dissipation is neglected. The maximally entangled state between the atoms and cavity field can be obtained under some certain conditions. The time of disentanglement of two atoms can be controlled and manipulated by adjusting the detuning and classical driving fields. Moreover, the larger the cavity decay rate is, the more quickly the entanglement of the two atoms decays.     

与压缩真空库耦合的单模腔内三量子点中激子纠缠

研究了与压缩真空库场耦合的单模腔中三个量子点中激子间纠缠的动力学行为.结果表明：如果不考虑腔模与激子吸收，激子演化为纯的纠缠态.当腔场与一压缩真空库耦合时，激子间形成混合三模高斯纠缠态；在长时极限下，激子态为一稳定的混合三模高斯纠缠态.通过求解激子的特征函数，发现激子态的纯度与纠缠不仅依赖于腔场的初态，并且还与库的双光子关联强度密切相关. 关键词： 纠缠 纯度 压缩真空库 量子点     

弱相干场耦合腔系统中的纠缠特性

研究由三个全同的二能级原子与耦合腔构成的系统, 考虑腔场处于弱相干态的情况. 采用Negativity熵度量两子系统间的纠缠, 利用数值计算方法研究了两个原子之间和两个腔场之间的纠缠性质. 讨论了腔场间的耦合系数和腔场的强度对纠缠特性的影响. 研究结果表明: 随光场强度增大, 原子间纠缠和腔场间纠缠均增强. 另一方面, 随耦合腔的耦合系数增大, 两原子间的纠缠减弱, 腔A和腔B间的纠缠增强; 而腔B和腔C间的纠缠, 以及腔A和腔C间纠缠与腔场间的耦合系数间存在非线性关系.     

驱动两能级原子和真空场相互作用系统中纠缠突然死亡的操控

利用并发度和线性熵作为纠缠度量研究了两个驱动两能级原子和真空场相互作用系统中的纠缠动力学特性,分析了经典驱动场频率、原子和经典场的耦合系数以及参数α对并发度和线性熵的影响。结果发现通过调控经典驱动场能够提高两原子之间和两原子与场之间的纠缠,实现两原子之间纠缠突然死亡现象的操控,理论上提供了一种调控纠缠的方式。     

Kerr介质对粒子数光场中双原子纠缠演化的影响

初始纠缠的双原子中的一个原子与高Q腔中的单模光场发生相互作用,我们分析了在真空场、粒子数场及Kerr介质环境下两原子间的纠缠演化特性,发现在真空条件下两原子的纠缠有规则的作周期性变化;在粒子数场中两原子的纠缠度严重衰减,演化过程中达到最大纠缠的几率大大减少,且在一定时间段内纠缠消失,产生纠缠猝死现象,随着粒子数增加,纠缠猝死区域不断增加,对两原子的纠缠造成极大地破坏;但当系统在Kerr介质环境中发生相互作用时,发现能有效消除粒子数场中产生的纠缠猝死现象,在一定条件下能使两原子间的纠缠度在高值状态窄幅震荡。     

Entanglement Transfer from Two-Mode Squeezed Vacuum State Field to Two Spatially Separated Atoms in Two-Photon Processes

We investigate the influence of the Stark shift on the entanglement transfer from the two-mode squeezed vacuum state field to two spatially separated atoms in two-photon processes. Our results show that the Stark shift plays an important role in such entanglement transfer. We find that when the Stark shift parameter r is small, the degree of entanglement between the two atoms increases with the increasing of the squeezing parameter ξ first, and after achieving its maximal value, the degree of entanglement will decrease to zero with the increasing of ξ; while for big r, E will increase with the increasing of ξ.     

Entropy Correlations and Entanglement of a Superconducting Charge Qubitin a Resonant Cavity in the Presence of Noise

We study the dynamics of the entropy correlations and entanglement in a system of interaction of a superconducting charge qubit with a single-mode resonant cavity subject to noise considered as two-state random phase telegraph noise. We show that although the noise has an apparent suppressing effect on the evolution of the entropies of the qubit and the field and also on the entanglement in the system, the entropy exchange between the qubit and the
field is independent of it during the time evolution of the system.     

Finite-time disentanglement induced by single-mode thermal field

In this paper, we study the entanglement dynamics of atoms locally coupled to a cavity field. By studying two different models within the framework of cavity QED, we show that the so-called atomic entanglement sudden death always occurs if initially the cavity field is in the thermal state, in clear contrast with that in the vacuum state where the same entanglement decay is in infinite time.     

陆续通过一个双模腔的两原子之间纠缠的突然产生和调控

通过计算并发度研究了陆续通过一个双模腔的两个原子之间的纠缠动力学特性, 讨论了第一个原子的相干性以及腔场初始纠缠度对两原子之间纠缠的影响. 结果表明系统在一定条件下可以出现两原子之间纠缠突然产生现象, 两原子之间产生纠缠的最大值依赖于双模腔场初始纠缠度; 并且可以通过改变原子的振幅来控制产生纠缠的阈值时间和纠缠的最大值, 理论上提供了一种调控纠缠的方式.     

Influence of Intrinsic Decoherence on Entanglement in Two-Qubit Quantum Heisenberg XYZ Chain

Taking the intrinsic decoherence effect into account, we investigate the time evolution of entanglement for two-qubit XYZ Heisenberg model in an external uniform magnetic field. Concurrence, the measurement of entanglement,is calculated. We show how the intrinsic decoherence modifies the time evolution of the entanglement and find that at short-time case, concurrence is oscillating as increasing magnetic field, which implies that entanglement may be enhanced or weakened in some time regions.     

Nonlocality and Multipartite Entanglement in Asymptotically Flat Space-Times

We study the Bell's inequality and multipartite entanglement generation for initially maximally entangled states of free Dirac field in a non inertial frame and asymptotically flat Robertson–Walker space-time.For two qubit case,we show that the Bell's inequality always is violated as measured by the accelerated observers which are in the causally connected regions.On the other hand,for those observers in the causally disconnected regions inequality is not violated for any values of acceleration.The generated three qubit state from two qubit state due to acceleration of one parties has a zero 3-tangle.For a three qubit state,the inequality violated for measurements done by both causally connected and disconnected observers.Initially GHZ state with non zero 3-tangle,in accelerated frame,transformed to a four qubit state with vanishing 4-tangle value.On the other hand,for a W-state with zero 3-tangle,in non inertial frame,transformed to a four qubit state with a non-zero 4-tangle acceleration dependent.In an expanding space-time with asymptotically flat regions,for an initially maximally entangled state,the maximum value of violation of Bell's inequality in the far past decreased in the far future due to cosmological particle creation.For some initially maximally entangled states,the generated four qubit state due to expansion of space-time,has non vanishing 4-tangle.     

Influence of Intrinsic Decoherence on Entanglement in Two-Qubit Quantum Heisenberg XYZ Chain

Taking the intrinsic decoherence effect into account, we investigate the time evolution of entanglement for two-qubit XYZ Heisenberg model in an external uniform magnetic field. Concurrence, the measurement of entanglement,is calculated. We show how the intrinsic decoherence modifies the time evolution of the entanglement and find that at short-time case, concurrence is oscillating as increasing magnetic field, which implies that entanglement may be enhanced or weakened in some time regions.     

两个V型三能级原子系统的纠缠突然死亡与复苏

研究了在真空辐射场作用下,两个V型三能级原子系统的纠缠随时间的演化特性.发现当两原子间距较远,自发辐射会导致纠缠退化,甚至导致纠缠突然死亡,而原子激发态衰变的速率会影响纠缠死亡的时间;当两原子间距非常小,由于原子间的合作效应,死亡后的纠缠会在一段时间后复苏,初始的纠缠和复苏的纠缠由不同的原因引起.     

k光子Jaynes-Cummings模型与运动原子相互作用中的熵交换及纠缠

文章研究了k光子Jaynes-Cummings模型与运动原子相互作用中的熵相互关系及纠缠特性.发现原子与光场之间具有熵交换特性.讨论了原子运动、光子数k和场模结构等因素对原子与光场熵相互关系的影响.此外,讨论了原子与场系统熵交换与纠缠之间的关系. 关键词： 熵交换 纠缠 Jaynes-Cummings模型 原子运动     

匀强及非匀强磁场中Heisenberg XXX链的纠缠研究

研究了匀强及非匀强磁场中反铁磁体Heisenberg XXX链的近邻和次近邻纠缠.结果表明对基态情形,纠缠随磁场B变化呈现阶梯型结构,这可用来构建量子纠缠"放大器"或量子纠缠"开关".对有限温度情形,引进一非匀强磁场Bi=(-1)iB可以使近邻格点间纠缠在某些区域明显增大,而次近邻格点间纠缠则完全消失;同时引进非匀强磁场Bi=(-1)iB还可以使近邻格点纠缠的临界温度Tcn增大,且Tcn随B的增大而升高,这意味着我们可以通过调节B的大小而在任意温度下得到纠缠.     

Macroscopic Superpositions and Entanglement of Mesoscopic Squeezed Vacuum States in Dissipative Cavity QED System

A scheme has been proposed for generating the macroscopic superpositions and the entanglement between the mesoscopic squeezed vacuum states by considering the two-photon interaction of N two-level atoms in a dissipative cavity with high quality factor assisted by a strong driving field. A number of multiparty entangled states between the atoms and the squeezed vacuum states, among the atoms, and among the squeezed vacuum states, can be prepared by virtue of a specific choice of the cavity detuning and the detuning of applied coherent field under the dissipation condition. The corresponding analytical expressions of the influence can be given. Moreover, we can also give a series of macroscopic entangled states between the usual coherent states and the squeezed vacuum states using the combination of the dissipative one-photon interaction Hamiltonian with the dissipative two-photon interaction Hamiltonian. We also discuss the experimental feasibility. Our scheme can be realized in the current techniques on the cavity QED.