Generation of maximally entangled atom pairs in driven dissipative cavity QED systems

We investigate the entanglement of an open tripartite system where a cavity field mode in thermal equilibrium is off-resonantly coupled with two atoms that are simultaneously driven by a resonant coherent field. For moderately detuned atom-field coupling and strong atomic driving we show the generation, at given interaction times and for low enough cavity decay rates, of atomic Bell states and of Bell state superpositions relevant for quantum gates implementation. The system can oscillate between bi-separable and fully separable states. Also we describe the distribution of quantum correlations between the atom-atom and the two atom-field subsystems. In the dispersive coupling regime with strongly driven atoms we show the generation of nearly stationary Bell states which remain protected from cavity dissipation.     

Kerr相互作用下量子相干性分布和量子信息流动

本文针对Kerr相互作用下系统中量子相干性的动力学分布进行了研究.所讨论系统包含两个没有相互作用的原子,每个原子都被囚禁在各自的光腔中,同时光腔被充满了非线性Kerr介质.研究发现非线性Kerr相互作用能够增加两原子间的量子相干性,而且增大的幅度会随着Kerr相互作用强度的增加而得以提高.其次,借助迹距离的方法,还探讨了非线性Kerr相互作用对于原子与光腔之间的量子信息流动的影响,发现Kerr相互作用可以加快量子信息回流到原子子系统中,抑制原子子系统与其余子系统间的量子信息交换,阻碍量子信息在系统中不同子系统间的流动,从而保护原子子系统中拥有的量子信息.     

利用腔QED实现量子态转移

利用两个二能级原子和用光纤联接的两个单模光腔构成的系统,给出了实现量子态转移的方案。该方案中两个二能级原子分别处于用光纤联接的单模腔中,并同时与光场发生共振相互作用。通过控制原子与光场的相互作用时间,实现量子态的转移。     

利用腔QED实现量子态转移

利用两个二能级原子和用光纤联接的两个单模光腔构成的系统,给出了实现量子态转移的方案。该方案中两个二能级原子分别处于用光纤联接的单模腔中,并同时与光场发生共振相互作用。通过控制原子与光场的相互作用时间,实现量子态的转移。     

Entanglement evolution and transfer in a double Tavis--Cumming model in cavity QED

We have studied entanglement evolution and transfer in a double Tavis--Cumming model where two pairs of entangled two-level atoms AB and CD interact with two single-mode cavity fields a and b. We show that the Bell-like initial state of atoms AB can exhibit entanglement sudden death which should be independent of the initial entanglement of atoms CD. Also, we show that the initial entanglement of one atomic pair can be transferred into another pair, as well as the possible subsystems, that become entangled during evolution.     

用腔场QED技术实现量子信息转移

提出了一种量子信息转移方案,它是基于两个耦合的二能级原子同时与单模腔场发生大失谐相互作用实现的.通过控制腔场与双原子的相互作用时间,量子信息可以从一个原子转移到另一个原子,或从单模腔场转移到双原子纠缠态上,而包含在欲转移量子态上的信息被完全檫除. 关键词： 大失谐Jaynes Cummings模型 量子信息转移 偶极 偶极相互作用     

Detecting Quantum Dissonance and Discord in Exact Dynamics of qubit Systems

In this paper, we evaluate the quantum and classical correlations in exact dynamics of qubit systems interacting with a common dephasing environment. We show the existence of a sharp transition between the classical and quantum loss of correlations during the time evolution. We show that it is possible to exploit a large class of initial states in different tasks of quantum information and processing without any perturbation of the correlations from the environment noisy for large time intervals. On the other hand, we include the dynamics of a new kind of correlation so-called quantum dissonance, which contains the rest of the nonclassical correlations. We show that the quantum dissonance can be considered as an indicator to expect the behavior of the dynamics of classical and quantum correlations in composite open quantum systems.     

Quantum correlations between two cavity QED systems coupled by a mechanical resonator

Achieving quantum correlations between two distant systems is a desirable feature for quantum networking. In this work, we study a system composed of two quantum emitter-cavity subsystems spatially separated. A mechanical resonator couples to either both quantum emitters or both cavities leading to quantum correlations between both subsystems such as non-local light-matter dressed states and cavity–cavity normal mode splitting. These indirect couplings can be explained by an effective Hamiltonian for large energy detuning between the mechanical resonator and the atoms/cavities. Moreover, it is found that the optimal conditions of the physical parameters maximize the entanglement of phonon-mediated couplings.     

Efficient Scheme for One-Way Quantum Computing in Thermal Cavities

We propose a practical scheme for one-way quantum computing based on efficient generation of 2D cluster state in thermal cavities. We achieve a controlled-phase gate that is neither sensitive to cavity decay nor to thermal field by adding a strong classical field to the two-level atoms. We show that a 2D cluster state can be generated directly by making every two atoms collide in an array of cavities, with numerically calculated parameters and appropriate operation sequence that can be easily achieved in practical Cavity QED experiments. Based on a generated cluster state in Box⁽⁴⁾ configuration, we then implement Grover’s search algorithm for four database elements in a very simple way as an example of one-way quantum computing.     

The Spectra of Quantum States and the Kronecker Coefficients of the Symmetric Group

Determining the relationship between composite systems and their subsystems is a fundamental problem in quantum physics. In this paper we consider the spectra of a bipartite quantum state and its two marginal states. To each spectrum we can associate a representation of the symmetric group defined by a Young diagram whose normalised row lengths approximate the spectrum. We show that, for allowed spectra, the representation of the composite system is contained in the tensor product of the representations of the two subsystems. This gives a new physical meaning to representations of the symmetric group. It also introduces a new way of using the machinery of group theory in quantum informational problems, which we illustrate by two simple examples.     

Dynamics of quantum discord in two Tavis-Cummings models with classical driving fields

We investigate the dynamics of quantum discord in a system consisting of two Tavis-Cummings models, each of which contains two atoms driven by a classical field. We compare the dynamics of quantum discord for the system with that of entanglement and show that quantum discord vanishes only asymptotically although entanglement disappears suddenly during the time evolution. Furthermore, we examine the influence of the initial states and the classical field on the discord dynamics and find that the value of quantum discord can be improved by adjusting the classical driving field. Finally, the quantum discord of two atoms in dissipative cavity is also discussed.     

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。     

Atomic Bell states generation in an open driven cavity QED system

We show that two uncorrelated two-level atoms can become maximally entangled if they are both off-resonantly coupled to a dissipative cavity mode, initially in the vacuum state, and strongly driven by a resonant coherent field. For moderate atom-field detuning we find that the quantum correlations in the tripartite system can alternatively concentrate either in the atom-atom subsystem or in the two atom-field subsystems. In the first case Bell states as well as their superpositions are generated for low enough cavity decay rates. In a dispersive coupling regime the atomic entanglement grows up monotonically to the maximum value where it remains nearly stationary without being affected by cavity dissipation.     

里德伯钠原子经绝热快速通道的布居数跃迁相干控制

运用含时多态展开方法和B-样条函数研究了啁啾频率微波场中里德伯钠原子的量子态之间的布居数迁移.计算了里德伯钠原子n=70-77的开普勒频率.计算了在不同的微波场中六个态的布居数从n=70到n=77随时间的迁移,布居数跃迁到最终态n=77达到了98%,这可以通过连续的单光子跃迁来实现.结果表明,通过优化微波脉冲参数可以实现从低态到较高态的布居跃迁的相干控制.     

Quantum information transfer between topological and conventional charge qubits

We propose a scheme to realize coherent quantum information transfer between topological and conventional charge qubits. We first consider a hybrid system where a quantum dot(QD) is tunnel-coupled to a semiconductor Majorana-hosted nanowire(MNW) via using gated control as a switch, the information encoded in the superposition state of electron empty and occupied state can be transferred to each other through choosing the proper interaction time to make measurements.Then we consider another system including a double QDs and a pair of parallel MNWs, it is shown that the entanglement information transfer can be realized between the two kinds of systems. We also realize long distance quantum information transfer between two quantum dots separated by an MNW, by making use of the nonlocal fermionic level formed with the pared Majorana feimions(MFs) emerging at the two ends of the MNW. Furthermore, we analyze the teleportationlike electron transfer phenomenon predicted by Tewari et al. [Phys. Rev. Lett. 100, 027001(2008)] in our considered system.Interestingly, we find that this phenomenon exactly corresponds to the case that the information encoded in one QD just returns back to its original place during the dynamical evolution of the combined system from the perspective of quantum state transfer.     

Entanglement Dynamics of Two Atoms in a Double Damping Jaynes-Cummings System

The entanglement between two stationary qubits is a kind of valuable quantum resources in quantum information or quantum network. This paper investigates the time evolution of the entanglement between two atoms, which are initially prepared in the Bell states and each of which interacts with its own cavity field in the identical and non-identical double damping Jaynes-Cummings (J-C) system. It mainly considers the effect of the atomic spontaneous decay Γ and the decay of cavity field κ on the two-qubit entanglement in such system. While causing the decay of entanglement, Γ and κ can also play a positive role in the entanglement evolution, which may imply a way to better control and maintain the entanglement. What is more, the rules governing the transfer of entanglement between two-qubit subsystems in strong coupling regime are finally studied by taking Γ and κ into consideration.     

Transfer of quantum correlations in nonunitary evolution

A generalized Lindblad equation has been derived for describing the evolution of two dynamical systems interacting with a bath formed by two broadband modes of squeezed light in an entangled state. The transfer of quantum correlations, in particular, entanglement between the bath and dynamic systems, which are taken in the form of two electromagnetic field modes separated by two high-Q cavities, two atoms, and an atom and a mode, has been analyzed. It has been found that the entanglement of the bath is transferred both to two modes and to two atoms, which can form an almost perfect Einstein-Podolsky-Rosen pair. It has been shown that the interaction of the bath with the system consisting of an atom and a mode for which collective boson operators are introduced leads to the appearance of coherent and squeezed states.     

Quantum discord between two moving two-level atoms

Considering a double JC model, this paper investigates the quantum discord dynamics of two isolated moving two-level atoms each interacting with a single-mode thermal cavity field, and studies the effect of the atomic motion and the field-mode structure on quantumdiscord. The results show that, on the one hand the quantum discord evolves periodically with time and the periods are affected by the atomic motion and the field-mode structure; on the other hand, the quantum discord still can capture the quantum correlation between the two atoms when the entanglement is zero. It is interesting to note that the quantum discord can be effectively preserved by controlling the field-mode structure parameter     

Influences of Detuning on Geometrical Quantum Discord in Coupled Cavities System

Geometrical quantum discord (GQD) is adopted to quantify the degree of correlation between two subsystems. We consider the situation that two two-level atoms are separately trapped in coupled single-mode cavities, and each atom non-resonantly interacts with cavity via a one-photon hopping. GQD dynamic between atoms and that between cavities are studied. The influences of detuning on GQD dynamics are discussed. The results obtained by the numerical method show that GQD between atoms is strengthened with the increase of the detuning. Contrarily, GQD between cavities is weakened with the increase of the detuning.