Entanglement dynamics of multiqubit system in Markovian and non-Markovian reservoirs

We study the entanglement dynamics of three qubits in contact with independent Markovian or non-Markovian reservoirs. The qubits are prepared in two types of GHZ-like or W-like states distinguished by initial excited-state populations. Though belonging to the same GHZ or W class of entanglement, the states with different initial excitations exhibit strikingly different dynamics. In addition, we show that the non-Markovian reservoirs can recover the multiqubit entanglement at instantaneous points or after a finite interval of entanglement disappearance. We also investigate the protection of multiqubit entanglement by the control of excitation emission via the detuning.     

Non-Markovian Effects on Entanglement Dynamics of Three Qubits

We investigate entanglement dynamics of three independent qubits each locally interacting with a zero-temperature non-Markovian reservoir. The effects of environment's amount of non-Markovianity or parameters in initial states on the three-qubit entanglement dynamics are presented in detail. It is found that the entanglement of such a system revives after a finite dark period when a proper degree of non-Markovian is present. A deep comparison to that in two-qubit system is also made.     

Entanglement Dynamics of Two Coupled Spins in a Spin Star Environment

We theoretically study the entanglement dynamics of two coupled spins in a spin star environment, whose elements are coupled to local bosonic baths. It is shown that the dynamics of the entanglement depends on the initial state of the system and the coupling strength between the two coupled central spins, the interactions between the central system and the environment, as well as interactions between the bath spin and the reservoir. We also investigate the effect of non-Markovian dynamics in contrast with the Markovian case. It is found that the non-Markovian dynamics has a significant effect on the disentanglement between the two central spins.     

Entanglement for Two-Qubit Extended Werner-Like States: Effect of Non-Markovian Environments

We investigate the sudden birth and sudden death of entanglement of two qubits interacting with uncorrelated structured reservoirs. The system is initially prepared in two-qubit extended Werner-like state. We work out the dependence of the entanglement dynamics on both non-Markovian environments and the purity of initial state, and show that non-Markovian environments and the purity can control the time of the two-qubit entanglement sudden death and the reservoirs' entanglement sudden birth.Furthermore, under the conditions of different purity and initial entanglement, the revival of qubits' entanglement can manifest before, simultaneously or even after the disentanglement of their corresponding reservoirs.     

Non-Markovian entanglement transfer to distant atoms in a coupled superconducting resonator

We investigate the non-Markovian effects on the entanglement transfer to the distant non-interacting atom qubits,which are embedded in a coupled superconducting resonator. The master equation governing the dynamics of the system is derived by the non-Markovian quantum state diffusion(NMQSD) method. Based on the solution, we show that the memory effect of the environment can lead to higher entanglement revival and make the entanglement last for a longer time. That is to say, the non-Markovian environment can enhance the entanglement transfer. It is also found that the maximum entanglement transferred to distant atoms can be modified by appropriately selecting the frequency of the modulated intercavity coupling. Moreover, with the initial anti-correlated state, the entanglement between the cavity fields can be almost completely transferred to the separated atoms. Lastly, we show that the memory effect has a significant impact on the generation of entanglement from the initial non-entangled states.     

Dynamics of genuine multipartite entanglement under local non-Markovian dephasing

We study dynamics of genuine entanglement for quantum states of three and four qubits under non-Markovian dephasing. Using a computable entanglement monotone for multipartite systems, we find that the GHZ state is quite resilient state whereas the W state is the most fragile. We compare dynamics of chosen quantum states with dynamics of random pure states and weighted graph states.     

非马尔科夫环境下耦合超导量子系统纠缠演化的数值研究

基于耦合超导量子比特系统模型下,在非马尔科夫环境中利用共生纠缠的方法分析了耦合系统纠缠的产生及其动力学的演化。研究了不同初始纠缠态下的纠缠猝死(ESD)和纠缠再生(ESB)现象;主要分析了系统耦合强度、库的截止频率与系统的振荡频率间的比值、温度和约瑟夫森能级差对纠缠演化的影响。结果表明:系统纠缠取决于初始纠缠态和系统的耦合强度J,并且通过调节以上非马尔科夫环境的相干参数可以延长解纠缠时间来确保量子计算过程中的应用和量子信息的实现。     

Quantum Entanglement in a Structured Reservoir

We study the entanglement dynamics of two-level atoms interacting in independent structured non-Markovian reservoirs. The atoms are initially prepared in a pure W state and the reservoir is in the vacuum. We have shown that the degree of entanglement of the initial states, Markovian environments can control the time of the two qubit entanglement sudden death and the reservoirs’ entanglement sudden birth. We show the dependence of entanglement dynamics on the non-Markovianity. When the initial state of atoms is in a pure W state, the entanglement will decay asymptotically.     

Quantum and classical correlations in a classical dephasing environment

We calculate the non-Markovian dynamics of quantum correlations, including entanglement and discord, and classical correlation in a two-qubit system with Ornstein-Uhlenbeck noise and discuss the relations in these correlations. It?s found that the initial-state parameters and the non-Markovian properties play an important role in these dynamics behaviors.     

Entanglement evolution in a non-Markovian environment

We extend recent theoretical studies of entanglement dynamics in the presence of environmental noise, following the long-time interest of Krzysztof Wodkiewicz in the effects of stochastic models of noise on quantum optical coherences. We investigate the quantum entanglement dynamics of two spins in the presence of classical Ornstein-Uhlenbeck noise, obtaining exact solutions for evolution dynamics. We consider how entanglement can be affected by non-Markovian noise, and discuss several limiting cases.     

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.     

Dynamics of Quantum Entanglement in Reservoir with Memory Effects

The non-Markovian dynamics of quantum entanglement is studied by the Shabani-Lidar master equation when one of entangled quantum systems is coupled to a local reservoir with memory effects.The completely positive reduced dynamical map can be constructed in the Kraus representation.Quantum entanglement decays more slowly in the non-Markovian environment.The decoherence time for quantum entanglement can be markedly increased with the change of the memory kernel.It is found out that the entanglement sudden death between quantum systems and entanglement sudden birth between the system and reservoir occur at different instants.     

Quantum correlation dynamics of three non-coupled two-level atoms in different reservoirs

Time evolution dynamics of three non-coupled two-level atoms independently interacting with their reservoirs is solved exactly by considering a damping Lorentzian spectral density.For three atoms initially prepared in Greenberger-Horne-Zeilinger-type state,quantum correlation dynamics in a Markovian reservoir is compared with that in a nonMarkovian reservoir.By increasing detuning quantity in the non-Markovian reservoir,three-atom correlation dynamics measured by negative eigenvalue presents a trapping phenomenon which provides long-time quantum entanglement.Then we compare the correlation dynamics of three atoms with that of two atoms,measured by quantum entanglement and quantum discord for an initial robuster-entangled type state.The result further confirms that quantum discord is indeed different from quantum entanglement in identifying quantum correlation of many bodies.     

Dynamics of entanglement protection of two qubits using a driven laser field and detunings:Independent and common,Markovian and/or non-Markovian regimes

Preventing quantum entanglement from decoherence effect is of theoretical and practical importance in the quantum information processing technologies.In this regard,we consider the entanglement dynamics of two identical qubits where the qubits which are coupled to two independent(Markovian and/or non-Markovian) as well as a common reservoir at zero temperature are further interacted with a classical driving laser field.Then,we study the preservation of generated two-qubit entanglement in various situations using the concurrence measure.It is shown that by applying the classical driving field and so the possibility of controlling the Rabi frequency,the amount of entanglement of the two-qubit system is improved in the off-resonance condition between the qubit and the central cavity frequencies(central detuning) in both non-Markovian and Markovian reservoirs.While the central detuning has a constructive role,the detuning between the qubit and the classical field(laser detuning) affects negatively on the entanglement protection.The obtained results show that long-living entanglement in the non-Markovian reservoir is more accessible than in the Markovian reservoir.We demonstrate that,in a common reservoir non-zero stationary entanglement is achievable whenever the two-qubit system is coupled to the reservoir with appropriate values of relative coupling strengths.     

Quantum correlations in non-Markovian environments

We have studied the analytical Markovian and non-Markovian dynamics of quantum correlations, such as entanglement, quantum discord and Bell nonlocalities for three noisy qubits. Quantum correlation as measured by quantum discord is found to be immune to death contrary to entanglement and Bell nonlocality for initial GHZ- or W-type mixed states.     

Correlation Dynamics of Three-Qubit System Under a Classical Dephasing Environment

By starting from the stochastic Hamiltonian of the three correlated spins and modeling their frequency fluctuations as caused by dephasing noisy environments described by Ornstein-Uhlenbeck (OU) processes, we study the dynamics of quantum correlations, including entanglement and quantum discord. Of course, in this article, we use two definitions for the quantum discord (global quantum discord and quantum dissension). We prepared initially our open system with the Greenberger-Horne-Zeilinger (GHZ) and W states and present the exact solutions for evolution dynamics of entanglement and quantum discord between three spins under both Markovian and non-Markovian regime of this classical noise. By comparison the dynamics of entanglement with that of quantum discord we find that entanglement can be more robust than quantum discord against this noise. It is shown that by considering non-Markovian extensions the survival time of correlations prolong. Also, we compare the results of two definitions of the quantum discord and show that the quantum dissension is equal to the global quantum discord for GHZ state, but they are unequal for the W state.     

Entanglement Evolution and Transfer in Non-Markovian Reservoirs

We study the dynamics of two entangled two-level atoms A and B which locally interact with independent reservoirs a and b, respectively. We consider the non-Markovian effects of reservoirs on the entanglement revival for the remote parties AB, ab, Ab and Ba after a simultaneous entanglement sudden death. In addition, we investigate the dynamics of multipartite entanglement that is created along with the decay of pairwise entanglement.     

Entanglement and non-Markovianity of a multi-level atom decaying in a cavity

We present a paradigmatic method for exactly studying non-Markovian dynamics of a multi-level V-type atom interacting with a zero-temperature bosonic bath. Special attention is paid to the entanglement evolution and the dynamical nonMarkovianity of a three-level V-type atom. We find that the entanglement negativity decays faster and non-Markovianity is smaller in the resonance regions than those in the non-resonance regions. More importantly, the quantum interference between the dynamical non-Markovianities induced by different transition channels is manifested, and the frequency domains for constructive and destructive interferences are found.     

Classical-driving-assisted coherence dynamics and its conservation

We investigate the quantum coherence and quantum entanglement dynamics of a classical driven single atom coupled to a single-mode cavity. It is shown that the transformation between the atomic coherence and the atom-field entanglement exists, and can be improved by adjusting the classical driving field. The joint evolution of two identical single-body systems is also studied. The results show the quantum coherence transfers among composite subsystems, and the coherence conservation of composite subsystems is obtained. Moreover, the classical driving field can be used to suppress the decay of the coherence and entanglement, owing to considering the leaky cavity. The non-Markovian dynamics of the system is also discussed finally.     

Non-Markovian dynamics of spin squeezing

We evaluate the spin squeezing dynamics of N independent spin-1/2 particles with exchange symmetry. Each particle couples to an individual and identical reservoir. We study the time evolution of spin squeezing under the influence of different decoherence. The spin squeezing property vanishes with evolution time under Markovian decoherence, while it collapses quickly and revives under non-Markovian decoherence. As spin squeezing can be regarded as a witness of multipartite entanglement, our scheme shows the collapses and revivals of multipartite entanglement under the influence of non-Markovian decoherence.