Collapse–revival of quantum discord and entanglement

In this paper the correlations dynamics of two atoms in the case of a micromaser-type system is investigated. Our results predict certain quasi-periodic collapse and revival phenomena for quantum discord and entanglement when the field is in Fock state and the two atoms are initially in maximally mixed state, which is a special separable state. Our calculations also show that the oscillations of the time evolution of both quantum discord and entanglement are almost in phase and they both have similar evolution behavior in some time range. The fact reveals the consistency of quantum discord and entanglement in some dynamical aspects.     

Effect of Dzialoshinski-Moriya interaction on the quantum discord of a spin-star model

The effect of Dzialoshinski-Moriya (DM) interaction on the quantum discord and the thermal entanglement of the density matrix of a spin star model is investigated. Our results imply that the quantum correlation measured by quantum discord and thermal entanglement can be established between two surrounding parties both of which have no interaction with each other but interact with the central party independently. From the analysis, we find that the strong DM interaction can enhance the quantum discord and thermal entanglement while the external magnetic field with a large value and the high temperature can shrink them. Specially, the quantum discord is more robust than the thermal entanglement in the sense that the range of parameters in which the quantum discord takes a zero value is much smaller than that of the thermal entanglement.     

Dynamics and protection of tripartite quantum correlations in a thermal bath

We study the dynamics and protection of tripartite quantum correlations in terms of genuinely tripartite concurrence, lower bound of concurrence and tripartite geometric quantum discord in a three-qubit system interacting with independent thermal bath. By comparing the dynamics of entanglement with that of quantum discord for initial GHZ state and W state, we find that W state is more robust than GHZ state, and quantum discord performs better than entanglement against the decoherence induced by the thermal bath. When the bath temperature is low, for the initial GHZ state, combining weak measurement and measurement reversal is necessary for a successful protection of quantum correlations. But for the initial W state, the protection depends solely upon the measurement reversal. In addition, the protection cannot usually be realized irrespective of the initial states as the bath temperature increases.     

基于腔QED系统的几何量子失谐及其传送

研究了基于腔量子电动力学（腔QED）系统的几何量子失谐及其传送。该系统包括两个独立的子系统,每个子系统由两个二能级原子与单模腔共振相互作用。结果表明,所有初始存储在原子A1A2中的几何量子失谐最终被转移到原子B1B2和腔C1C2。同时,原子A1A2 ,B1B2和腔C1C2的几何量子失谐在该量子系统中可以发生猝死（DSD）以及纠缠突然死亡（ESD）。但是,在该量子系统中几何量子失谐不能完全由于原子的自发辐射和腔衰减而复活。此外,原子A1A2 ,B1B2和腔C1C2几何量子失谐的量,取决于其纯度p,并与其成比例,p的值越小,几何失谐越小。它也表明,在原子自发辐射和腔衰减的情况下,原子A1A2 ,B1B2和腔C1C2的几何量子失谐将经历振荡衰减并最终衰减到零。不过,在没有原子自发辐射和腔衰减的情况下,原子A1A2 ,B1B2和腔C1C2的几何量子失谐却没有衰减。     

基于腔QED系统的几何量子失谐及其传送

研究了基于腔量子电动力学（腔QED）系统的几何量子失谐及其传送。该系统包括两个独立的子系统,每个子系统由两个二能级原子与单模腔共振相互作用。结果表明,所有初始存储在原子A1A2中的几何量子失谐最终被转移到原子B1B2和腔C1C2。同时,原子A1A2 ,B1B2和腔C1C2的几何量子失谐在该量子系统中可以发生猝死（DSD）以及纠缠突然死亡（ESD）。但是,在该量子系统中几何量子失谐不能完全由于原子的自发辐射和腔衰减而复活。此外,原子A1A2 ,B1B2和腔C1C2几何量子失谐的量,取决于其纯度p,并与其成比例,p的值越小,几何失谐越小。它也表明,在原子自发辐射和腔衰减的情况下,原子A1A2 ,B1B2和腔C1C2的几何量子失谐将经历振荡衰减并最终衰减到零。不过,在没有原子自发辐射和腔衰减的情况下,原子A1A2 ,B1B2和腔C1C2的几何量子失谐却没有衰减。     

Dynamics of Quantum Discord of Two-Qubit Coupled with a Vacuum Cavity

The dynamical behaviors of quantum discord between two atoms coupled with a vacuum cavity are investigated. If the two qubits are initially prepared in two extended Werner-like states, the quantum discord and entanglement can be numerically calculated. There are remarkable differences between the time evolutions of the quantum discord and entanglement under the same conditions. These results imply that quantum discord is not zero for some unentangled states and in some regions entanglement can disappear completely. A large amount of quantum discord exists between the two-qubit. Thus, the quantum discord is more robust than entanglement for the quantum system exposed to the environment. The quantum discord shows sudden change and its existence depends on the initial state of the system. This property of quantum discord may have important implications for experimental characterization of quantum phase transitions.     

两二能级原子在共同环境下的量子关联动力学

通过精确求解带有偶极-偶极相互作用的两个二能级原子与一个共同热库相互作用模型, 得到了两原子间量子纠缠和量子失谐(quantum discord)的解析表达式. 综合考虑了环境的非马尔可夫效应、原子间的偶极-偶极相互作用以及原子的本征频率同腔模中心频率之间的失谐量对两原子间量子纠缠和quantum discord的影响. 研究显示: 在非马尔可夫机制下, 且原子的本征频率与腔模中心频率是共振时, 当两原子初态处于纠缠态时, 原子间偶极-偶极相互作用可以显著抑制包括量子纠缠和quantum discord等量子关联的衰减, 更特别的是, 如果原子的本征频率同腔模中心频率有一定的失谐时, 利用原子间偶极-偶极相互作用可大大地延长两原子退纠缠的时间; 当两原子初态处于可分离态时, 从短时间来看, 原子间偶极-偶极相互作用可以提高量子纠缠和quantum discord振荡的振幅,而在长时间极限下, 原子间偶极-偶极相互作用不会改变量子纠缠和quantum discord达到的稳定值. 最后, 讨论了原子间偶极-偶极相互作用对量子纠缠和quantum discord动力学不同的影响. 关键词： 量子纠缠 量子失谐 共同环境 偶极-偶极相互作用     

压缩真空态中原子与场的量子纠缠和量子discord

在压缩真空库中,研究了原子与场的相互作用下二比特体系的量子discord和量子纠缠的动力学行为.重点分析了原子的初始态系数和压缩真空库的压缩系数对量子纠缠和量子discord的影响.通过数值分析我们得到,随着原子的初始态系数和压缩真空库的压缩系数值的增加,量子纠缠和量子discord都会减小,但量子纠缠比量子discord减小的更快一些.最后研究了在原子的初始态系数和压缩真空库的压缩系数的值相同的情况下,量子discord比量子纠缠存在的时间更长些.     

Creation of quantum correlations between two atoms in a dissipative environment from an initial vacuum state

We have investigated the effect of counter-rotating terms on the dynamics of entanglement and quantum discord between two identical atoms interacting with a lossy single mode cavity field for a system initially in a vacuum state. The counter-rotating terms are found to lead to steady states in the long-time limit which can have high quantum discord, but have no entanglement. The effect of cavity decay rate on this steady-state quantum discord has been also investigated, surprisingly, the increase in cavity decay rate is found to enhance the steady-state quantum discord.     

Entanglement Dynamics and Bell Violations of Two Atoms in Tavis-Cummings Model with Phase Decoherence

Considering the dipole-dipole coupling intensity between two atoms and the field in the Fock state, the entanglement dynamics between two atoms that are initially entangled in the system of two two-level atoms coupled to a single mode cavity in the presence of phase decoherence has been investigated. The two-atom entanglement appears with periodicity without considering phase decoherence, however, the phase decoherence causes the decay of entanglement between two atoms, with the increasing of the phase decoherence coefficient, the entanglement will quickly become a constant value, which is affected by the two-atom initial state. Meanwhile the two-atom quantum state will forever stay in the maximal entangled state when the initial state is proper even in the presence of phase decoherence. On the other hand, the Bell violation and the entanglement do not satisfy the monotonous relation, a large Bell violation implies the presence of a large amount of entanglement under certain conditions, while a large Bell violation corresponds to a little amount of entanglement in certain situations. However, the violation of Bell-CHSH inequality can reach the maximal value if two atoms are in the maximal entangled state, or vice versa.     

Quantum Discord of Two Atoms Interacting with a Single-mode Thermal Field

This paper investigates the quantum discord and entanglement of two atoms when they simultaneously interact with a single-mode thermal field. The results show that, the two atoms which are initially in separate states can be entangled by a thermal field. However, with increase of the mean photon number, the value of the entanglement decreases and disappears when the temperature of the cavity is high enough (corresponding to the large value of the mean photon number). In stark contrast, the quantum discord does not decrease, but gradually reaches stable value at high temperature. In addition, when the two atoms are initially the Werner mixed state, we have found that, a large amount of quantum discord is exist even in the region where the entanglement is zero, which is a strong signature for the presence of non classical correlations. These results indicate that, the quantum discord is more resistant to the environment’s disturbance than the entanglement for higher temperatures.     

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.     

量子关联与原子间相互作用距离关系的研究

本文将两个二能级原子注入一个腔中,用共生纠缠的方法来度量两原子之间的纠缠并推出它们之间的量子失协,还给出了原子与环境之间的共生纠缠与量子失协的计算公式,讨论了原子自发衰变率的变化对量子纠缠及失协的影响,及不同的初始状态情况下,纠缠及失协随原子距离的演化情况。结果表明：原子自发衰变率减小,原子与环境之间的量子纠缠及失协增加;选择不同的初态,可以控制原子间出现纠缠死亡的现象或量子失协为零的状态。     

Tavis-Cummings模型中的几何量子失协特性

采用几何量子失协的计算方法,通过改变两原子初始状态、腔内光子数和偶极-偶极相互作用强度,研究了Tavis-Cummings模型中的几何量子失协特性.结果表明:几何量子失协都是随时间周期性振荡的,选取适当的初态可以使两原子一直保持失协状态,增加腔内光子数和偶极相互作用对几何量子失协有积极的影响.     

量子关联与原子间相互作用距离关系的研究

本文将两个二能级原子注入一个腔中,用共生纠缠的方法来度量两原子之间的纠缠并推出它们之间的量子失协,还给出了原子与环境之间的共生纠缠与量子失协的计算公式,讨论了原子自发衰变率的变化对量子纠缠及失协的影响,及不同的初始状态情况下,纠缠及失协随原子距离的演化情况。结果表明：原子自发衰变率减小,原子与环境之间的量子纠缠及失协增加;选择不同的初态,可以控制原子间出现纠缠死亡的现象或量子失协为零的状态。     

量子关联与原子间相互作用距离关系的研究

本文将两个二能级原子注入一个腔中,用共生纠缠的方法来度量两原子之间的纠缠并推出它们之间的量子失协,还给出了原子与环境之间的共生纠缠与量子失协的计算公式,讨论了原子自发衰变率的变化对量子纠缠及失协的影响,及不同的初始状态情况下,纠缠及失协随原子距离的演化情况.结果表明:原子自发衰变率减小,原子与环境之间的量子纠缠及失协增加;选择不同的初态,可以控制原子间出现纠缠死亡的现象或量子失协为零的状态.     

Tavis-Cummings模型中两纠缠原子纠缠的演化特性

研究了两个纠缠的两能级原子与单模粒子数场进行相互作用系统中两原子的纠缠演化.结果表明：两个原子之间的纠缠呈现出周期性的演化特性，初始两原子的状态、原子之间的偶极相互作用和粒子数场对腔中两个原子的纠缠有着显著的影响.发现适当选择原子的初态，两原子会永远处于最大纠缠态. 关键词： 量子纠缠 偶极-偶极相互作用 部分转置矩阵负本征值 纠缠原子     

Quantum correlations between two non-interacting atoms under the influence of a thermal environment

By considering a double Jaynes-Cummings model, we investigate the dynamics of quantum correlations, such as the quantum discord and the entanglement, for two atoms in their respective noisy environments, and study the effect of the purity and the cavity temperature on the quantum correlations. The results show that the entanglement suffers sudden death and revival, however the quantum discord can still reveal the quantum correlations between the two atoms in the region where the entanglement is zero. Moreover, when the temperature of each cavity is high the entanglement dies out in a short time, but the quantum discord still survives for quite a long time. It means that the quantum discord is more resistant to environmental disturbance than the entanglement at higher temperatures.     

强度相关耦合双Jaynes-Cummings模型中的纠缠和量子失谐

研究强度相关耦合双Jaynes-Cummings模型中, 两运动原子初始处于最大纠缠态、光场初始处于单模热态时, 强度相关耦合、热光场平均光子数以及原子运动对两原子的纠缠和量子失谐的影响. 结果表明: 考虑强度相关耦合时, 纠缠和量子失谐均出现周期性地消失和回复现象, 并且, 回复以后的纠缠和量子失谐能达到初始值. 腔场温度的升高会加速纠缠和量子失谐的消失. 此外, 原子运动的场模结构参数对该模型中的纠缠和量子失谐影响很大, 其值选择合适时, 两个原子能够自始至终地保持纠缠或量子失谐状态. 关键词： 强度相关耦合 双Jaynes-Cummings模型 纠缠 量子失谐