Distillability sudden death in a two qutrit systems under a thermal reservoir

The dynamics of distillability entanglement between qutrit-qutrit systems interacting with a thermal reservoir is investigated in this paper.We discovered an interesting phenomenon that under a thermal reservoir certain initially prepared free-entangled states become bound-entangled states in a finite time,which is called distillability sudden death(DSD).We use a realignment criterion to measure the nine-dimensional density matrix of the entanglement.Moreover,we analyze some other parameters to investigate the effects to the systems.Explanations are then given.     

T-C模型中光场和原子以及原子与原子之间的纠缠演化

研究了T-C模型中的二能级原子与单模场以及两个二能级原子之间不同初态的纠缠演化.发现,它们之间的形成纠缠是周期演化的,不同初态纠缠演化的周期不同.在一种类W初态下两原子之间还出现所谓的纠缠猝灭现象. 关键词： T-C模型 纠缠度 纠缠猝死     

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.     

Effect of pure phase decoherence on entanglement teleportation

We study entanglement teleportation in the two‐qubit XX Heisenberg model with pure phase decoherence taken into account. For some initial entangled states, pure phase decoherence has no effect on the teleported entanglement, while for others pure phase decoherence has a pronounced effect. In addition, entanglement sudden death happens in the latter case.     

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.     

Dynamics of Entanglement for a Two-Parameter Class of States in a Qubit-Qutrit System

We investigate the dynamics of entanglement for a two-parameter class of states in a hybrid qubit-qutrit system under the influence of various dissipative channels. Our results show that entanglement sudden death (ESD) is a general phenomenon and it usually takes place in a qubit-qutrit system interacting with various noisy channels, not only the case with dephasing and depolarizing channels observed by others. ESD can only be avoided for some initially entangled states under some particular noisy channels. Moreover, the environment affects the entanglement and the coherence of the system in very different ways.     

Entanglement evolution of a two-qubit system with decay beyond the rotating-wave approximation

The entanglement property of two identical atoms, initially entangled in Bell states, coupled to a single-mode cavity is considered. Based on the reduced non-perturbative quantum master equation method, the entanglement evolution of the two atoms with decay is investigated beyond the conventional rotating-wave approximation. We show that the counter-rotating wave terms, usually neglected, have a great influence on the disentanglement behaviour of the system. The phenomena of entanglement sudden death and entanglement sudden birth will occur. In addition, we show that the entanglement can be strengthened by introducing the dipole--dipole interaction of the two atoms.     

Entanglement and decoherence of coupled superconductor qubits in a non-Markovian environment

The sudden death of entanglement is investigated for the non-Markovian dynamic process of a pair of interacting flux qubits under a thermal bath. The results show that, for initially two-qubit entangled states, entanglement sudden death (ESD) always happens in the thermal reservoir, where its appearance strongly depends on the environment. In particular, ESD of the qubits occurs more easily for the non-Markovian process than for the Markovian one.     

Entanglement dynamics of two distant atoms in two detuning cavities

We investigate the entanglement dynamics via the concurrence of two distant atoms interacting off-resonantly with two cavity fields in Fock states,respectively.We find that the evolution of entanglement has sudden death and sudden birth phenomena,that with the increase of photon numbers in the two cavities,the alternate frequency of sudden death and sudden birth turns fast,and that the amplitude of concurrence oscillates regularly with oscillation frequency becoming slow when the cavity fields have the same photon numbers.While,the maximum of concurrence declines and the amplitude of concurrence oscillates irregularly when the two cavity fields have different photon numbers.In addition,we find the length of death time is dependent on the initial entanglement.     

Entanglement sudden death of two atoms interacting with a cavity via the two-photon process in a strong-driving-assisted system

We examine the entanglement dynamics between two strongly driven atoms off-resonantly coupled with a single-mode cavity via the two-photon process with the help of negativity in two different types of initial states. The results show that entanglement sudden death may occur under both the above conditions and the sudden death effect can be monitored by modulating the atom--cavity detunings. Furthermore, we also find an atomic decoherence-free subspace so that the initial entanglement between two atoms remains invariable in application.     

控制Tavis-Cummings模型中两原子X态的纠缠突然死亡与突然产生

研究了初态为X态时Tavis-Cummings模型中具有偶极相互作用两原子的纠缠演化特性,在演化过程中,同时号码出现了两原子的纠缠突然死亡(ESD)与突然产生(ESB)两种有趣的现象.详细分析了两原子初始态的纯度、偶极相互作用、光场粒子数对这两种现象出现时间的影响,进一步给出了初始为混态时ESB与ESD的转换条件.计算结果表明,上述系统参量对两原子的纠缠演化、ESB与ESD有重要的影响,偶极相互作用会改变纠缠度的振荡周期,使出现ESD的时间间隔减少;随着初始两原子纠缠纯度的增大,纠缠突然产生以及纠缠突然死亡存在的时间缩短,并且可以提高两原子之间的纠缠;对于特殊的初态,产生了纠缠不变性以及固定的两原子纠缠,该定值受两原子初始状态的纯度控制。     

Entanglement transfer via two arrays of coupled resonator waveguides

We propose a scheme for transferring entanglement through two independent arrays of coupled resonator waveguides, where a three-level atom is embedded in each resonator. We investigate the entanglement dynamics of the transferred state. The influence of initial states and applied lasers on the entanglement sudden death phenomenon is also discussed. Furthermore, we study the dynamics of pairwise quantum correlations measured by the quantum discord.     

Relation between initial conditions and entanglement sudden death for two-qubit extended Werner-like states

In this paper, the dynamical behavior of entanglement of an uncoupled two-qubit system, which interacts with inde- pendent identical amplitude damping environments and is initially prepared in the extended Werner-like （EWL） states, is investigated. The results show that whether entanglement sudden death （ESD） of an EWL state will occur or not depends on initial purity and concurrence. The boundaries between ESD states and ESD-free states for two kinds of EWL states are found to be different. Furthermore, some regions are shown where ESD states can be transformed into ESD-free states by local unitary operations.     

Sudden death of entanglement of a quantum model

In this paper the so-called sudden death effect of entanglement is investigated in a quantum model. The results show that one can expect the resurrection of the original entanglement to occur in a periodic way following each sudden death event. The length of the time interval for the zero entanglement depends not only on the degree of entanglement of the initial state but also on the initial state.     

Distillability of Sudden Death in Qutrit-Qutrit Systems under Global Mixed Noise

Considering the influences of collective dephasing, multilocal qutrit-flip, local qutrit-flip, and the combination of global mixed noise, we study the dynamics of entanglement and the phenomenon of distillability of sudden death (DSD) in a qutrit-qutrit system under various decoherent noises. It is shown that the system always undergoes DSD when it interacts with multilocal and local qutrit-flip noise, and the time-determined bound entangled state is more dependent on different noises. Comparing with the cases of global mixed and collective dephasing noise,we conclude that the qutrit-flip noise is responsible for the DSD.     

Entanglement evolution of three-qubit mixed states in multipartite cavity—reservoir systems

We analyze the multipartite entanglement evolution of three-qubit mixed states composed of a GHZ state and a W state.For a composite system consisting of three cavities interacting with independent reservoirs,it is shown that the entanglement evolution is restricted by a set of monogamy relations.Furthermore,as quantified by the negativity,the entanglement dynamical property of the mixed entangled state of cavity photons is investigated.It is found that the three cavity photons can exhibit the phenomenon of entanglement sudden death(ESD).However,compared with the evolution of a generalized three-qubit GHZ state which has the equal initial entanglement,the ESD time of mixed states is later than that of the pure state.Finally,we discuss the entanglement distribution in the multipartite system,and point out the intrinsic relation between the ESD of cavity photons and the entanglement sudden birth of reservoirs.     

Entanglement dynamics of two-bipartite system under the influence of dissipative environments

An experimental scheme is suggested that permits a direct measure of entanglement in a two-qubit cavity system. It is realized in the cavity-QED technology utilizing atoms as flying qubits. With this scheme we generate two different measures of entanglement, namely logarithmic negativity and concurrence. The phenomenon of sudden death entanglement (ESD) in a bipartite system subjected to dissipative environment is examined. We show that the sudden death time of the entangled states depends on the initial preparation of the entangled state and the temperature of the reservoir.     

Secure key from bound entanglement

We characterize the set of shared quantum states which contain a cryptographically private key. This allows us to recast the theory of privacy as a paradigm closely related to that used in entanglement manipulation. It is shown that one can distill an arbitrarily secure key from bound entangled states. There are also states that have less distillable private keys than the entanglement cost of the state. In general, the amount of distillable key is bounded from above by the relative entropy of entanglement. Relationships between distillability and distinguishability are found for a class of states which have Bell states correlated to separable hiding states. We also describe a technique for finding states exhibiting irreversibility in entanglement distillation.     

三量子比特Dicke模型中的两体和三体纠缠动力学

本文利用绝热近似方法和精确对角化方法研究三量子比特Dicke模型中的纠缠动力学.处于两种典型的纠缠态GHZ态和W态上的量子比特在时间演化过程中与辐射光场发生强耦合作用,在各种子系统间产生纠缠,通过分析这些纠缠的演化特性发现初始GHZ态的三体纠缠鲁棒性比W态强,这与旋波近似结论一致.与旋波近似下结果不同的是,两种态中任意...