Cross correlation between the two modes in two-photon Jaynes-Cummings model in the presence of a classical homogeneous gravitational field

The temporal evolution of both the atomic population inversion of an effective two-level atom and the cross correlation between the two modes in two-photon Jaynes-Cummings model in the presence of a classical homogeneous gravitational field are investigated. To analyse the dynamical evolution of the atom-radiation system a quantum treatment of the internal and external dynamics of the atom is presented based on an alternative su(2) dynamical algebraic structure. By solving the Schr?dinger equation in the interaction picture, the evolving state of the system is found by which the influence of the gravitational field on the dynamical behavior of both the atomic population inversion of an effective two-level atom and the cross correlation between the two modes of the radiation field are explored. Assuming that initially the radiation field is prepared in the coherent state for each mode and an effective two-level atom is in a coherent superposition of the excited and ground states, the influence of gravity on both the atomic population inversion of an effective two-level atom and the cross correlation between the two modes of the radiation field are studied.     

Gravitational Jaynes–Cummings model beyond the rotating wave approximation

In this paper, the quantum properties of a two-level atom and the cavity-field in the Jaynes?CCummings model with the gravity beyond the rotating wave approximation are investigated. For this purpose, by solving the Schr?dinger equation in the interaction picture, the evolving state of the system is found by which the influence of the counter-rotating terms on the dynamical behaviour of atomic population inversion and the probability distribution of the cavity-field as quantum properties is explored. The results in the atom?Cfield system beyond the rotating wave approximation with the gravity show that the quantum properties are not completely suppressed under certain conditions.     

Monte Carlo wavefunction approach to the dissipative quantum-phase dynamics of two-component Bose-Einstein condensates

We investigate the relaxation effects on the dynamics of two-component dilute gas Bose-Einstein condensates (BEC) with relatively different two-body interactions and Josephson couplings between the two components. Three types of relaxation effects, i.e., one- and three-body losses and a pure phase relaxation caused by elastic two-body collision between condensed and noncondensed atoms, are examined on the dynamical behavior of a macroscopic superposition, i.e., Schr?dinger cat state, of two states with atom-number differences between the two components, which is known to be created by the time evolution in certain parameter regimes. Although three-body losses show a relatively large suppression of the revival behavior of Schr?dinger cat state and the Pegg-Barnett phase-difference distribution between the two components for a small-size Schr?dinger cat state, one- and three-body loss effects are not shown to directly depend on the size of Schr?dinger cat state. In contrast, the pure-phase relaxation effects, causing a reduction of phase-difference distribution and then decaying the Schr?dinger cat state, significantly increase with the increase of the size of Schr?dinger cat state. These features suggest that a detection of damped collapse-revival behavior is highly possible for medium-size Schr?dinger cat states in small-size two-component BECs.     

Cosmology with inhomogeneous magnetic fields

We review spacetime dynamics in the presence of large-scale electromagnetic fields and then consider the effects of the magnetic component on perturbations to a spatially homogeneous and isotropic universe. Using covariant techniques, we refine and extend earlier work and provide the magnetohydrodynamic equations that describe inhomogeneous magnetic cosmologies in full general relativity. Specialising this system to perturbed Friedmann–Robertson–Walker models, we examine the effects of the field on the expansion dynamics and on the growth of density inhomogeneities, including non-adiabatic modes. We look at scalar perturbations and obtain analytic solutions for their linear evolution in the radiation, dust and inflationary eras. In the dust case we also calculate the magnetic analogue of the Jeans length. We then consider the evolution of vector perturbations and find that the magnetic presence generally reduces the decay rate of these distortions. Finally, we examine the implications of magnetic fields for the evolution of cosmological gravitational waves.     

Dynamic properties of wehrl information entropy and wehrl phase distribution for a moving four-level atom

We study the dynamics of the von Neumann entropy, Wehrl entropy, and Wehrl phase distribution for a single four-level ladder-type atom interacting with a one-mode cavity field taking into account the atomic motion. We obtain the exact solution of the model using the Schr¨odinger equation under specific initial conditions. Also we investigate the quantum and classical quantifiers of this system in the nonresonant case. We examine the effects of detuning and the atomic motion parameter on the entropies and their density operators. We observe an interesting monotonic relation between the different physical quantities in the case of nonmoving and moving atoms during the time evolution. We show that both the detuning and the atomic motion play important roles in the evolution of the Wehrl entropy, its marginal distributions, entanglement, and atomic populations.     

Atomic Entropy in the Gravitational Jaynes-Cummings Model with Respect to Counter-Rotating Terms

In this paper, the dynamical evolution of the entanglement of gravitational Jaynes-Cummings model with respect to counter-rotating terms is examined. First, in the gravitational the Jaynes-Cummings model with respect to counter-rotating terms the effective Hamiltonian of the Schr?dinger equation in the interaction picture is obtained. Then, by transforming the Schr?dinger equation to two differential equations, the amplitudes of probability are obtained. In this case, by obtaining the entanglement of the system, its time evolution in the presence of certain parameters is investigated.     

耗散腔中Λ型原子与光场Raman相互作用体系的线性熵

为了研究耗散腔中原子与光场Raman相互作用体系中子系统间的熵交换,利用超算符方法通过对系统主方程求解,讨论了光场强度、腔的耗散系数及原子两能级的Stark位移对线性熵的影响.结果表明：光场越强,光场与其它子系统进行熵交换的时间越长|腔耗散系数越大,熵交换时间越短|改变两能级间的Stark位移使原子和场之间的耦合增强,而系统的耗散系数不变,此时,系统的熵交换加快且其稳态值变小.     

Preparation and decoherence of superpositions of electromagnetic field states

In a recent experiment the progressive decoherence of a mesoscopic superposition of two coherent field states in a high-Q cavity, known as Schr?dinger cat state, has been measured for the first time [Brune et al., Phys. Rev. Lett. 77, 4887 (1996)]. Here, the full master equation governing the coupled dissipative dynamics of the atom-field system studied in the experiment is formulated and solved numerically for the experimental parameters. The model simulated avoids the approximations underlying an analytically solvable model which is based on a harmonic expansion of the energies of the dressed atomic states and on a treatment of their dynamics within the adiabatic approximation. In particular, the numerical simulations reveal that the coupling of the cavity field mode to its environment causes important decoherence effects already during the initial preparation phase of the Schr?dinger cat state. This phenomenon is investigated in detail with the help of a measure for the purity of states. Moreover, the Hilbert-Schmidt distance of the intended target state, the Schr?dinger cat, to the state that is actually prepared in the experiment is determined. Received 13 September 2000 and Received in final form 22 December 2000     

Influence of a Classical Homogeneous Gravitational Field on Dissipative Dynamics of the Phase Damped Jaynes–Cummings Model under the Markovian Approximation

In this paper, we study the dissipative dynamics of the phase damped Jaynes–Cummings model under the Markovian approximation in the presence of a classical homogeneous gravitational field. The model consists of a moving two-level atom simultaneously exposed to the gravitational field and a single-mode traveling radiation field in the presence of a phase damping mechanism. We first present the master equation for the reduced density operator of the system under the Markovian approximation in terms of a Hamiltonian describing the atom-field interaction in the presence of a homogeneous gravitational field. Then, by making use of the super-operator technique, we obtain an exact solution of the master equation. Assuming that initially the radiation field is prepared in a Glauber coherent state and the two-level atom is in the excited state, we investigate the influence of gravity on the temporal evolution of collapses and revivals of the atomic population inversion, atomic dipole squeezing, atomic momentum diffusion, photon counting statistics and quadrature squeezing of the radiation field in the presence of phase damping.     

Entropy squeezing for a two-level atom in two-mode Raman coupled model with intrinsic decoherence

In this paper, we investigate the entropy squeezing for a two-level atom interacting with two quantized fields through Raman coupling. We obtain the dynamical evolution of the total system under the influence of intrinsic decoherence when the two quantized fields are prepared in a two-mode squeezing vacuum state initially. The effects of the field squeezing factor, the two-level atomic transition frequency, the second field frequency and the intrinsic decoherence on the entropy squeezing are discussed. Without intrinsic decoherence, the increase of field squeezing factor can break the entropy squeezing. The two-level atomic transition frequency changes only the period of oscillation but not the strength of entropy squeezing. The influence of the second field frequency is complicated. With the intrinsic decoherence taken into consideration, the results show that the stronger the intrinsic decoherence is, the more quickly the entropy squeezing will disappear. The increase of the atomic transition frequency can hasten the disappearance of entropy squeezing.     

Atom-field entanglement in two-atom Jaynes-Cummings model with nondegenerate two-photon transitions

An exact solution of the problem of two two-level atoms with nondegenerate two-photon transitions and nondegenerate Raman transitions interacting with two-mode radiation field is presented. Asymptotic solutions for system state vectors are obtained in the approximation of large initial coherent fields. The atom-field entanglement is investigated on the basis of the reduced atomic entropy dynamics. The possibility of the system being initially in a pure disentangled state to revive into this state during the evolution process for both models is shown. Conditions and times of disentanglement are derived.     

重力场中的熵产生研究

重力场中的大气处于非平衡态，其温度是空间的函数，不同的等温面之间要产生热流，从而改变熵的空间分布。本文推导出重力场中的熵产生公式，并描绘出熵产生随高度变化的近似曲线。     

Effects of bias on dynamics of an AC-driven two-electron quantum-dot molecule

The effects of bias on the dynamical localization of two interacting electrons in a pair of coupled quantum dots driven by external AC fields have been numerically investigated. With an effective two-site model and Floquet formalism,the time-dependent Schroedinger equation is numerically solved and the Pmin, the minimum of the population evolution of the initial state within a certain time period, is used to quantify the degree of the dynamical localization. Results indicate that the bias can change the energy of the initial state and break the dynamical symmetry of the system with a pure AC field. And the amplitude of the AC field with dynamical localization phenomenon changes with bias. All the numerical results are explained by the perturbation theory and two-level approximation.     

Relativistic Dynamics of Vector Bosons in the Field of Gravitational Radiation

We consider a model of the state evolution of relativistic vector bosons, which includes both the dynamical equations for the particle four-velocity and the equations for the polarization four-vector evolution in the field of a nonlinear plane gravitational wave. In addition to the gravitational minimal coupling, tidal forces linear in curvature tensor are suggested to drive the particle state evolution. The exact solutions of the evolutionary equations are obtained. Birefringence and tidal deviations from the geodesic motion are discussed.     

Linear Entropy and Entanglement in Two-Charge-Qubit Circuits

We consider a model that contains two coupled superconducting charge qubits by sharing a large Josephson junction. We examine the dynamical properties of the linear entropy of two qubits and the probability of both qubits being in an excited state. The results show that the initial mean photon number, the initial phase of the field and the relative phase of the two qubits＇ levels play an important role in the evolution of the linear entropy of the two qubits and the probability.     

Quantum Phase and Field Purification for Quantum System in Coherent States Based on Generalized Heisenberg Algebra

In this paper, we consider the interaction between the two-level atom and the electromagnetic field modes initially prepared in coherent states associated with the generalized Heisenberg algebra (GHA). We investigate the dynamical behavior of the field purity, Pancharatnam phase, and atomic-population inversion. Based on the GHA, we study the statistical properties of the field state through the evolution of the Mandel parameter and examine the effects of the initial atomic state setting and the number of transiting photons. The results show that the GHA-coherent-state strength has the potential to affect the time evolution of the field purification, the Pancharatnam phase, and the Mandel parameter.     

Entanglement and Pancharatnam Phase of a Four-Level Atom in Coherent States Within Generalized Heisenberg Algebra

We consider a four-level atom (FLA) interacting with a field mode that is initially in a coherent state associated with a generalized Heisenberg algebra (CSGHA). The dynamical behavior of quantum entropy, the Pancharatnam phase, and the Mandel parameter are investigated. The statistical and nonclassical properties of the field in regard to its CSGHA are discussed through the evolution of the Mandel parameter, and the effects of the initial atomic state position and time-dependent coupling given in terms of atomic speed and acceleration are examined. The results show that the CSGHA strength and time-dependent coupling based on the atomic speed and acceleration have the potential to affect the time evolution of the entanglement, the Pancharatnam phase, and the Mandel parameter.     

Influence of Lamb Shift Parameter on Dissipative Dynamics of the Phase Damped Jaynes–Cummings Model with Gravity Under Markovian Approximation

In this paper, we study the dissipative dynamics of the phase damped Jaynes–Cummings model with gravity under Markovian approximation in the presence of the Lamb shift parameter. The model consists of a moving two-level atom simultaneously exposed to the gravitational field and a single-mode traveling radiation field in the presence of a phase damping mechanism. We first present the master equation for the reduced density operator of the system under Markovian approximation in terms of a Hamiltonian describing the atom-field interaction with gravity in the presence of Lamb-shift parameter. Then, by making use of the super-operator technique, we obtain an exact solution of the master equation. Assuming that initially the radiation field is prepared in a Glauber coherent state and the two-level atom is in the excited state, we investigate the influence of Lamb shift parameter on the temporal evolution of collapses and revivals of the atomic population inversion, atomic dipole squeezing and atomic momentum diffusion in the presence of phase damping.     

On entropy production

We investigate the case of a dynamical system when irreversible time evolution is generated by a nonHermitian superoperator on the states of the system. We introduce a generalized scalar product which can be used to construct a monotonically changing functional of the state, a generalized entropy. This will depend on the level of system dynamics described by the evolution equation. In this paper we consider the special case when the irreversibility derives from imbedding the system of interest into a thermal reservoir. The ensuing time evolution is shown to be compatible both with equilibrium thermodynamics and the entropy production near the final steady state. In particular, Prigogine’s principle of minimum entropy production is discussed. Also the limit of zero temperature is considered. We present comments on earlier treatments.