相位阻尼腔中依赖强度Jaynes-Cummings模型的线性熵

在大失谐近似和腔场与库之间耦合假设存在相位阻尼的条件下，通过展示原子、场和原子-场系统的线性熵研究了由含任意强度耦合的Jaynes-Cummings模型描述的量子系统演化规律，讨论了相位阻尼对系统的纠缠及相干性丢失效应。     

The physical transient spectrum for a V-type three-level atom interacting with a binomial field via multi-photon process and nonlinearities

We study the interaction of a multi-photon three-level atom with a single mode field in a cavity, taking explicitly into account the existence of forms of nonlinearities of both the field and the intensitydependent atom-field coupling. The analytical form of the emission spectrum is calculated using the dressed states of the system. The effects of photon multiplicities, mean photon number, detuning, Kerr-like medium, and the intensity-dependent coupling functional on the emission spectrum are analyzed.     

Two-Qubit Local Fisher Information Correlation beyond Entanglement in a Nonlinear Generalized Cavity with an Intrinsic Decoherence

In this paper, we study a Hamiltonian system constituted by two coupled two-level atoms (qubits) interacting with a nonlinear generalized cavity field. The nonclassical two-qubit correlation dynamics are investigated using Bures distance entanglement and local quantum Fisher information under the influences of intrinsic decoherence and qubit–qubit interaction. The effects of the superposition of two identical generalized coherent states and the initial coherent field intensity on the generated two-qubit correlations are investigated. Entanglement of sudden death and sudden birth of the Bures distance entanglement as well as the sudden changes in local Fisher information are observed. We show that the robustness, against decoherence, of the generated two-qubit correlations can be controlled by qubit–qubit coupling and the initial coherent cavity states.     

Entanglement of a General Formalism V-Type Three-Level Atom Interacting with a Single-Mode Field in the Presence of Nonlinearities

We investigate the evolution of the atomic quantum entropy and the atom-field entanglement in a system of a V-configuration three-level atom interacting with a single-mode field with additional forms of nonlinearities of both the field and the intensity-dependent atom-field coupling. With the derivation of the unitary operator within the frame of the dressed state and the exact results for the state of the system we perform a careful investigation of the temporal evolution of the entropy. A factorization of the initial density operator is assumed, considering the field to be initially in a squeezed coherent or binomial state. The effects of the mean photon number, detuning, Kerr-like medium and the intensity-dependent coupling functional on the entropy are analyzed.     

Collapse-revival phenomenon for different configurations of a three-level atom interacting with a field via multi-photon process and nonlinearities

General formalisms of a three-level atom interacting with quantized fields under the mechanism of the multi-photon transition are investigated. The wave function is calculated in the context of the framework of the dressed states. The collapse-revival phenomenon dependence on the photon number is discussed. The influences of detuning, Kerr-like, coupling constants and various forms of the intensity-dependent coupling functional are analyzed. General conclusions reached are illustrated through numerical results.     

Entropy and entanglement in the mixed state for a dispersive JC model in a phase-damped cavity

Temporal evolution is studied for total entropy, the entropy difference and the sum of negative eigenvalues of the partially transposed density matrix as quantitative entanglement measurements for JC model in a phase-damped cavity in the dispersive approximation. The cavity field is assumed to be coupled to a reservoir with a phase-damping coupling. The case of a statistical mixture (SM) of coherent states is considered as initial field state. The effects of cavity phase damping on the entanglement between the field and the atom are studied.     

Entanglement of a multi-photon three-level atom interacting with a single-mode field in the presence of nonlinearities

General formalisms of a three-level atom in different configurations (namely, V, ??, and ?? configurations) interacting with multi-photon process of a single-mode field are investigated. Analytical expressions of the unitary operator within the framework of the dressed states and density operators of the consideration systems are derived. The temporal evolution of atomic quantum entropy when the field is initially in the binomial state and the atom is initially in its upper most state is considered. The effect of multiplicity, Kerr-like medium, detuning and different forms of intensity-dependent coupling functional on the degree of entanglement (DEM) are discussed. Details of the phenomenon differ from one configuration to the other.     

Entanglement Dynamics of Linear and Nonlinear Interaction of Two Two-Level Atoms with a Quantized Phase-Damped Field in the Dispersive Regime

In this paper we study the linear and nonlinear (intensity-dependent) interactions of two two-level atoms with a single-mode quantized field far from resonance, while the phase-damping effect is also taken into account. To find the analytical solution of the atom-field state vector corresponding to the considered model, after deducing the effective Hamiltonian we evaluate the time-dependent elements of the density operator using the master equation approach and superoperator method. Consequently, we are able to study the influences of the special nonlinearity function \(f (n) = \sqrt {n}\), the intensity of the initial coherent state field and the phase-damping parameter on the degree of entanglement of the whole system as well as the field and atom. It is shown that in the presence of damping, by passing time, the amount of entanglement of each subsystem with the rest of system, asymptotically reaches to its stationary and maximum value. Also, the nonlinear interaction does not have any effect on the entanglement of one of the atoms with the rest of system, but it changes the amplitude and time period of entanglement oscillations of the field and the other atom. Moreover, this may cause that, the degree of entanglement which may be low (high) at some moments of time becomes high (low) by entering the intensity-dependent function in the atom-field coupling.     

Entanglement in a general formalism of a V -type three-level atom interacting with a correlated two-mode cavity field in the presence of nonlinearities

We consider a V-configuration three-level atom interacting with two modes of light in a cavity with arbitrary nonlinearities of both the fields and the intensity-dependent atom?Cfield coupling. We assume a factorized initial-density operator, with the privileged field modes being in a pair-coherent state. We analyze the effects of the mean photon number, detuning, Kerr-like medium, and the intensitydependent coupling functional on the entropy.     

Entanglement Dynamics in a Model Tripartite Quantum System

A Λ-type atom interacting with two radiation fields exhibits electromagnetically induced transparency and other nonclassical effects that appear in the entanglement dynamics of the atomic subsystem and in appropriate field observables. Both EIT and field-atom entanglement are important for quantum information processing. We investigate the roles played by specific initial field states, detuning parameters, field nonlinearities and intensity-dependent field-atom couplings on EIT and the entanglement between subsystems. Departure from coherence of the initial field states produces significant effects. We investigate these aspects in a model that exhibits the salient features of entangled tripartite systems. For initial photon-added coherent states, collapses and revivals of the atomic subsystem von Neumann entropy appear as the intensity parameter varies over a narrow range of values. These features could be useful in enabling entanglement.     

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。     

Quantum Entropy of a Four-Level Atom with Arbitrary Nonlinearities

General formalisms of a four-level atom in different configurations interacting with a single mode quantized electromagnetic field under multi-photon process with additional forms of nonlinearities of both the field and the intensity-dependent atom-field coupling are investigated. Analytical expressions for the time unitary evolution operator and density operator are obtained. The atom is prepared in its upper most and the field is prepared in a binomial state. The effects of the mean photon number, photon multiplicity, detuning, Kerr-like medium and the intensity-dependent coupling functional on the entropy are considered. General conclusions reached are illustrated by numerical results.     

Symmetric structure of the field and atomic squeezing in a quantum optical model

At resonance, the symmetric structure of the field and atomic squeezing has been exposed in the Jaynes-Cummings model when it is restricted to the following initial condition: the atom in the ground state and the field in the superposition of the vacuum and one-photon state. The influence of the detuning, the virtual-photon processes, intensity-dependent coupling and the presence of a Kerr-like medium on the symmetric structure has also been discussed.     

利用依赖强度的非共振相互作用实现纠缠信息的完全交换

利用全量子理论,分析了多个原子-腔场构成的联合系统中原子与腔场依赖强度的非共振相互作用过程.结果表明:通过控制原子与腔场相互作用时间,并对原子状态进行测量,原子最大纠缠态与类奇偶相干态光场的最大纠缠态可以相互转换;对失谐量的限制,使得二者之间完全交换,进一步证明封闭系统中的演化是可逆的.     

Non-Markovian effects on entanglement dynamics in lossy cavities

We consider the non-markovian entanglement dynamics of two independent atoms, each off-resonantly coupling with a zero temperature reservoir. For two types of initial entanglement, corresponding to spin correlated and anti-correlated Bell-like states |φ〉 and |ψ〉, we study the dependence of the two-qubit entanglement transfer on both the off-resonant interactions and the cavity pseudomode decay. The speed of the entanglement transfer is related to the choice of the atom detuning from the cavity pseudomode, the cavity pseudomode decay and the relative coupling. Furthermore, compared to the ideal cavities, entanglement transfer and sudden death can not be prevented using off-resonant interactions in the lossy cavities, and the conservation rules are always satisfied in the off-resonant and lossy system.     

Continuous-Variable Entanglement Generation from a Four-State Atom under Raman Excitation

We investigate the generation and the evolution of continuous-variable (CV) entanglement from a laser-driven four-state atom inside a doubly resonant cavity under Raman excitation. Two transitions in the four-state atom independently interact with the two cavity modes, while two other transitions are driven by coupling laser fields. By including the atomic relaxation as well as cavity losses, we show that the CV entanglement with large mean number of
photons can be generated in our scheme. We also show that the intensity of the coupling laser fields can influence effectively the entanglement period of the cavity field. Different from the conventional resonant excitation scheme where zero one-photon detuning are required, it is found that the intensity and period of entanglement between the two cavity modes as well as the total mean photon number of the cavity field can be adjusted by properly
modulating the frequency detuning.     

Entanglement Between Two Dipole-Coupled Qubits Interacting with Two Independent Slightly Detuned Cavity Modes

Considering the generalized double Jaynes-Cummings model, we examine the entanglement between two non-identical dipole-dipole coupled qubits interacting with two independent detuned vacuum cavity modes. We calculate the negativity as a measure of qubits entanglement. We find that entanglement parameter evolve periodically with time and the period are affected by the model parameters and initial states of qubits. For unentangled initial states the detuning and dipole-dipole interaction affect only the period of entanglement oscillations, not the maximum value of entanglement. For entangled states the detuning stabilizes the entanglement parameter oscillations. According to choice of initial entangled state the dipole-dipole strength is greatly enhances or weakens the oscillations of the entanglement parameter.

     

Dynamical creation of entanglement versus disentanglement in a system of three-level atoms with vacuum-induced coherences

The dynamics of entanglement between three-level atoms coupled to the common vacuum is investigated. We show that the collective effects such as collective damping, dipole-dipole interaction and the cross coupling between orthogonal dipoles, play a crucial role in the process of creation of entanglement. In particular, the additional cross coupling enhances the production of entanglement. For the specific initial states we find that the effect of delayed sudden birth of entanglement, recently invented by Ficek and Tana? [Ficek, R. Tana?, Phys. Rev. A 77 (2008) 054301] in the case of two-level atoms, can also be observed in the system. When the initial state is entangled, the process of spontaneous emission causes destruction of correlations and its disentanglement. We show that the robustness of initial entanglement against the noise can be changed by local operations performed on the state.     

Control and Transfer of Entanglement between Two Atoms Driven by Classical Fields under Dressed-State Representation

We have studied the dynamics and transfer of the entanglement of the two identical atoms simultaneously interacting with vacuum field by employing the dressed-state representation. The two atoms are driven by classical fields. The influence of the initial entanglement degree of two atoms, the coupling strength between the atom and the classical field and the detuning between the atomic transition frequency and the frequency of classical field on the entanglement and atomic linear entropy is discussed. The initial entanglement of the two atoms can be transferred into the entanglement between the atom and cavity field when the dissipation is neglected. The maximally entangled state between the atoms and cavity field can be obtained under some certain conditions. The time of disentanglement of two atoms can be controlled and manipulated by adjusting the detuning and classical driving fields. Moreover, the larger the cavity decay rate is, the more quickly the entanglement of the two atoms decays.     

Linear entropy in the Jaynes-Cummings model with a Kerr nonlinearity

The dynamical properties of quantum entanglement in the integrable Jaynes-Cummings model with a Kerr nonlinearity are studied in terms of the reduced-density linear entropy with various Kerr coupling parameters and initial states, where the initial states are prepared by the coherent states placed in the corresponding phase space described in terms of canonical variables. The mean entanglement averaged over time is employed to investigate the behavior of entanglement of those coherent states. It is shown that the mean entanglement of the coherent states put near the centers of periodic orbits, both with a strong Kerr coupling and without a Kerr coupling, tends to be the minimal, and that the mean entanglement of the coherent states centered near the boundary with a strong Kerr coupling is the minimal while that without Kerr coupling is the maximal.