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。     

类克尔介质光腔中原子的纠缠动力学研究

初始处于纠缠的原子与附加类克尔介质的光腔相互作用,运用共生纠缠的度量方法对原子间的纠缠演化动力学进行研究,分析了腔场粒子数、介质非线性效应及原子与腔场的失谐量对纠缠演化的影响,发现处于腔场真空态下原子间的纠缠作周期性震荡演化,而处在腔场粒子数态下的原子在演化过程中发生纠缠突然死亡现象;在非线性克尔介质作用下,处于腔场粒子数较小范围内(n≤5)的原子间也会产生纠缠突然死亡现象;但随着腔场粒子数的增加纠缠突然死亡现象消失而且一定程度上可以达到纠缠初始值;当腔场处于任意粒子数态时,由于非线性效应的影响,均可抑制纠缠突然死亡现象的发生;当腔场在没有类克尔介质作用时,原子与腔场间的失谐量同样可以避免纠缠突然死亡现象的发生.     

耦合双Tavis-Cummings模型中的纠缠演化和转移特性

研究了由光纤模连接的两个Tavis-Cummings模型中纠缠演化和纠缠转移的特性。结果表明,初始两原子间的纠缠可转移为另两原子间的纠缠,在纠缠转移过程中,光纤模起到中间传递的作用。纠缠的转移与初始两原子间的纠缠、原子与腔场的耦合强度以及光纤模与腔场的耦合强度、原子与腔场的失谐量和腔场耗散有关。初始纠缠决定了另两原子间纠缠产生的大小;在原子与腔场的耦合强度一定的条件下,随着光纤模与腔场耦合强度的增强,纠缠转移的时间缩短,且产生的纠缠值增加;腔场耗散对纠缠演化的衰减影响是显著的,而失谐量的增加可以有效地抑制这一现象。在整个纠缠转移过程中,系统中其他任两子体系间的纠缠起到了桥梁的作用,实现了两量子纠缠态的远程传递和制备。     

原子的选择测量对原子纠缠特性和场熵的影响*

考虑初始处于W态的三个二能级原子,将其中两个原子同时注入处于真空态的单模腔中,并与光场发生共振相互作用的情况。采用数值计算方法,通过对是否进行原子态选择性测量情况下,腔内原子间的纠缠性质和场熵的比较,讨论了对腔外原子的态选择性测量对腔内原子间的纠缠性质和场熵演化的影响。研究结果表明：对腔外原子的选择性测量,可增强腔内原子间的纠缠,但会减弱腔內原子与光场的关联。     

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.     

与热库耦合的光学腔内三原子间的纠缠动力学

研究了与热库耦合的光学腔中三个相互作用的二能级原子间的纠缠动力学.采用拉普拉斯变换和下限共生等方法,通过数值计算,分析了原子间三体纠缠的演化以及腔场与热库间的两体纠缠演化,讨论了各耦合参数对系统纠缠演化的影响.研究结果表明:原子间纠缠在短时间内随着原子间耦合强度的增加而增加,随原子与腔场耦合强度的增加而减小,在长时极限下趋于一稳定值;体系的非马尔科夫性由原子与腔场的耦合强度以及热库的谱宽度共同决定,当热库与腔场为强耦合时,原子与腔场组成的系统遵循非马尔科夫动力学,此时随着热库谱宽的增加,原子系统由非马尔科夫性变为马尔科夫性,随着谱宽的继续增加,原子与腔场组成的系统遵循马尔科夫动力学,原子系统又表现出非马尔科夫性;调整腔场与热库的失谐可以有效抑制热库耗散对纠缠衰减的影响.     

双光子J-C模型实现非定域双原子系统量子特性的远程控制

考虑一对纠缠的二能级原子之一与单模腔场发生双光子共振相互作用,经腔QED演化后,对腔场进行光子探测,通过操纵相互作用的时间和光场参数以及初态两纠缠原子的纠缠度,可远程调控腔外原子表现出更强的非经典效应,如原子的偶极压缩;同时使用相同的方法对远程控制的信道-原子间的纠缠演化也进行了控制,从而更有效地实现对原子量子特性的控制.并且发现原子的压缩和原子间的纠缠存在一定的对应关系.     

粒子数场对双原子纠缠演化的影响

考虑初始处于纠缠态的两原子,分别以一定的速率依次通过高Q粒子数场,利用negativity度量纠缠的方法,研究了两原子之间的纠缠演化与原子初态和光场状态的关系,并与两原子同时在腔场时的情况做了比较.发现:当粒子数场为真空场时,两种模型下双原子纠缠度均做周期性演化;当粒子数场为非真空场时,双原子纠缠度都会出现纠缠猝死现象.并进一步研究了该现象随初始纠缠参量θ、粒子数n的变化关系以及与环境(腔场)的纠缠转移问题.     

远程控制原子的纠缠特性

考虑初始处于GHZ态的三个二能级原子,将其中两个原子同时注入处于真空态的单模腔中,并与光场发生共振相互作用的情况.利用全量子理论和采用数值计算方法,研究了腔内原子的纠缠性质.通过对是否进行腔外原子态选择性测量和腔外原子旋转操作情况下,腔内原子间的纠缠性质的比较,讨论了对腔外原子的旋转操作和测量对腔内原子间纠缠性质的影响.研究结果表明：若没有对腔外原子进行旋转操作,腔内两原子是分离的|若对腔外原子进行旋转操作和选择性测量,腔内两原子是纠缠的.另一方面,腔内两原子间的纠缠性质随旋转角的变化具有对称性,其对称轴为θ=π/2,可通过控制旋转角度的大小来控制腔内原子间的纠缠度.     

腔量子电动力学系统中耦合三原子的纠缠特性

研究了三个全同二能级原子与单模腔相互作用系统中原子间的三体纠缠特性.考虑原子间存在相互耦合,并且腔场处于弱相干态的情况,通过数值计算给出了纠缠量的演化曲线,讨论了原子间耦合强度和弱相干场强度对三体纠缠的影响.研究结果表明:随弱相干场强度增强,原子间的三体纠缠增强;相反,随原子间耦合系数增大,原子间三体纠缠减弱.     

Controlling entanglement sudden death in cavity QED by classical driving fields

We investigate the entanglement dynamics of a quantum system consisting of two-level atoms interacting with vacuum or thermal fields with classical driving fields. We find that the entanglement of the system can be improved by adjusting the classical driving field. The influence of the classical field and the purity of the initial state on the entanglement sudden death is also studied. It is shown that the time of entanglement sudden death can be controlled by the classical driving fields. Particularly, the entanglement sudden death phenomenon will disappear if the classical driving fields are strong enough.     

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。     

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.     

Sudden death of entanglement: Classical noise effects

When a composite quantum state interacts with its surroundings, both quantum coherence of individual particles and quantum entanglement will decay. We have shown that under vacuum noise, i.e., during spontaneous emission, two-qubit entanglement may terminate abruptly in a finite time [T. Yu, J.H. Eberly, Phys. Rev. Lett. 93 (2004) 140404], a phenomenon termed entanglement sudden death (ESD). An open issue is the behavior of mixed-state entanglement under the influence of classical noise. In this paper we investigate entanglement sudden death as it arises from the influence of classical phase noise on two qubits that are initially entangled but have no further mutual interaction.     

Entanglement dynamics of non-interacting two-qubit system under a squeezed vacuum environment

Entanglement dynamics of two non-interacting atoms in a squeezed vacuum reservoir is studied. Several examples with different initial entangled states are investigated, and it is found that entangled atoms become disentangled faster in squeezed vacuum than in ordinary vacuum, and larger squeezing results in faster entanglement decay. The time evolution of the concurrence and the separability "distance" A can be used to explain this novel entanglement sudden death phenomenon.     

Sudden birth versus sudden death of entanglement for the extended Werner-like state in a dissipative environment

In this paper, we investigate the dynamical behaviour of entanglement in terms of concurrence in a bipartite system subjected to an external magnetic field under the action of dissipative environments in the extended Werner-like initial state. The interesting phenomenon of entanglement sudden death as well as sudden birth appears during the evolution process. We analyse in detail the effect of the purity of the initial entangled state of two qubits via Heisenberg XY interaction on the apparition time of entanglement sudden death and entanglement sudden birth. Furthermore, the conditions on the conversion of entanglement sudden death and entanglement sudden birth can be generalized when the initial entangled state is not pure. In particular, a critical purity of the initial mixed entangled state exists, above which entanglement sudden birth vanishes while entanglement sudden death appears. It is also noticed that stable entanglement, which is independent of different initial states of the qubits (pure or mixed state), occurs even in the presence of decoherence. These results arising from the combination of the extended Werner-like initial state and dissipative environments suggest an approach to control and enhance the entanglement even after purity induced sudden birth, death and revival.     

远程制备双原子纠缠态

提出一种远程制备双原子纠缠态的方案,该方案基于两个原子与单模腔场的同时非共振相互作用.由于双粒子纠缠态比三粒子纠缠态容易制备,方案用两对双原子纠缠态作为量子通道.Alice 拥有的两个相同原子同时与一单模腔场非共振相互作用.Alice已知她要制备的纠缠态,她选择适当的相互作用时间、测量她所拥有的两个原子并通过经典通道通知Bob.Bob引入一个相同的辅助原子和一个单模腔场来实现方案.方案对腔场状态和腔损耗不敏感,基于当前的腔QED 技术,方案能在实验上实现.该方案有望在量子信息过程中有重要的应用价值.     

Tunable entanglement sudden death and three-partite entanglement in Tavis-Cummings model with an added nonlinear kerr-like medium

We investigate the entanglement dynamics and the phenomenon of entanglement sudden death in the two-photon Tavis-Cummings model with an added nonlinear kerr-like medium. It is shown that the phenomenon of entanglement sudden death can be controlled by the nonlinear kerr-like medium. Furthermore, the influence of dipole-dipole interaction on entanglement between atoms is also discussed. It is found that the phenomenon of entanglement sudden death can be weakened by the dipole-dipole interaction. Finally, we investigate the influence of kerr medium and dipole-dipole interaction on the three-partite entanglement of the system by making use of the state preparation fidelity.     

Entanglement Dynamics of the Double Intensity-Dependent Coupling Jaynes-Cummings Models

We consider entanglement dynamics of double intensity-dependent coupling Jaynes-Cummings models with two different initial light fields, which one is in the squeezed vacuum state and another is in the coherent state. The results show that, when the compressibility factor and the mean photon number are smaller, the concurrence of atoms exhibits phenomenon of dead and revival periodically, and the entanglement perfectly transferres between the atoms and the fields. As the value of them grow larger, the entanglement sudden death and sudden revival come out. Comparing with the normal double Jaynes-Cummings model, we notice that the concurrence of the atoms which in the normal double Jaynes-Cummings models evolves irregularly. And it is find that periodical entanglement pulse can be generated by using double intensity-dependent coupling Jaynes-Cummings models. This result might be useful in quantum information processes.