Nonstationary effects in the system of coupled quantum dots influenced by Coulomb correlations

We investigate the time evolution of filling numbers of localized electrons in the system of two coupled single-level quantum dots (QDs) connected with the continuous-spectrum states in the presence of Coulomb interaction. We consider correlation functions of all orders for electrons in the QDs by decoupling higher-order correlations between localized and band electrons in the reservoir. We analyze different initial charge configurations and consider Coulomb correlations between localized electrons both within the dots and between the different dots. We reveal the presence of a dynamical charge trapping effect in the first QD in the situation where both dots are occupied at the initial instant. We also find an analytic solution for the time-dependent filling numbers of the localized electrons for a particular configuration of the dots.     

A parity conserving dimer model with infinitely many absorbing states

We propose and study a model where two aspects are present: parity conservation and infinitely many absorbing states. Whereas steady-state simulations show that the static critical behaviour is not affected by the presence of multiple absorbing configurations, the influence of the initial state associated with the presence of slowly decaying memory effects is clearly displayed in time dependent simulations. We report results of a detailed investigation of the dependence of critical spreading exponents on the initial particle density. Received 13 January 1999 and Received in final form 7 April 1999     

Nature of quantum recurrences in coupled higher dimensional systems

We investigate recurrence phenomena in coupled two degrees of freedom systems. It is shown that an initial well localized wave packet displays recurrences even in the presence of coupling in these systems. We discuss the interdependence of time scales namely classical period and quantum revival time and explain the significance of initial conditions.     

The role of Hubbard-like interaction in the dynamics of two interacting electrons

We study the effects of a Hubbard-like interaction on the dynamics of two electrons restricted to move in a linear chain. Our calculations suggest that the presence of bounded two-electron states in the initial Gaussian wave-packet plays significative roles on both unbiased and the electric-field biased wave-packet dynamics.     

Influence of Intrinsic Decoherence in the Presence of Stark Shift on Nonclassical Properties of the Two-Mode JCM

We study the influence of intrinsic decoherence in the presence of Stark shift for the two-mode Jaynes—Cummings model (JCM). An analytic solution of the Milburn equation for the multiquant two-mode JCM Hamiltonian is obtained. We use this solution to investigate the influence of intrinsic decoherence and Stark shift on nonclassical properties of the system, for the resonant and the off-resonant cases. We compare the behavior of the system in the case of having a coherent superposition state and a statistical mixture of coherent states as an initial field.     

Quenching dynamics of a quantum XY spin-1/2 chain in the presence of transverse field by the application of a generalized Landau-Zener formula

In this paper we review the quenching dynamics of a quantum XY spin-1/2 chain in the presence of a transverse field, when the transverse field or the anisotropic interaction is quenched at a slow but uniform rate. We also extend the results to the cases in which the system starts with any arbitrary initial condition as opposed to the initial fully magnetically aligned state which has been extensively studied earlier. The evolution is non-adiabatic in the time interval when the parameters are close to their critical values, and is adiabatic otherwise. The density of defects produced due to nonadiabatic transitions is calculated by mapping the many-particle system to an equivalent Landau-Zener problem. We show that in one dimension the density of defects in the final state scales as 1/√τ irrespective of the initial condition, where τ is the quenching time-scale. However, the magnitude of density of defects is found to depend on the initial condition.      

Thermal Entanglement Between a Jaynes-Cummings Atom and an Isolated Atom

We studied the entanglement of a quantum system consisting of a Jaynes-Cummings atom, thermal lossless cavity and an isolated atom. The analytical expressions of the atom-atom negativity for separable and entangled initial atomic states were obtained. The influence of a detuning between the atomic transition frequency and the field frequency and direct dipole-dipole interaction on an atom-atom entanglement is examined. We showed that for a separable initial atomic states a detuning might cause high atom-atom entanglement in the presence of the dipole-dipole interaction. We also obtained that for an entangled initial atomic state a detuning causes a stabilization of an entanglement oscillations both for model with dipole-dipole interaction and model without such interaction.     

Nonlinear development of the dust acoustic instability in acollisional dusty plasma

We study the nonlinear behavior of the low-frequency dust acoustic instability in a collisional dusty plasma by means of particle simulations. The instability arises due to the streaming of plasma ions and neutrals relative to charged dust grains. According to linear theory, the presence of collisions between the plasma ions and a neutral gas background reduces the growth rate of the instability. Nonlinearly, however, the presence of drifting neutrals maintains the initial relative drift between plasma and dust ions until the unstable waves grow to large amplitude and collisions due to wave-particle interactions exceed the neutral collisions. As a result, stronger nonlinear effects, as manifested by enhanced fluctuations, larger amounts of plasma and dust heating, and a temporary reduction of the relative drift velocity, can occur in the presence of collisions     

Self-consistency of the quantum billiard problem in wormhole spacetimes

A wormhole can be made to function as a time machine. In the context of the quantum billiard problem in the presence of a wormhole we examine whether this is compatible with the self-consistency of physics. We derive a self-consistency condition in which the classical limit corresponds to known results for the (classical) billiard problem in a wormhole space-time and that suggests that some fine-tuning of initial conditions might be necessary.     

Quantum Field Theory and Dense Measurement

We show, using quantum field theory (QFT), that performing a large number of identical repetitions of the same measurement does not only preserve the initial state of the wave function (the Zeno effect), but also produces additional physicaleffects. We first discuss the Zeno effect in the framework of QFT, that is, as a quantum field phenomenon. We then derive it from QFT for the general case in which the initial and final states are different. We use perturbation theory and Feynman diagrams and refer to the measurement act as an external constraint upon the system that corresponds to the perturbative diagram that denotes this constraint. The basic physical entities dealt with in this work are not the conventional once-perfomed physical processes, but their n times repetition where n tends to infinity. We show that the presence of these repetitions entails the presence of additional excited state energies, and the absence of them entails the absence of these excited energies.     

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.     

Dynamics of Spin-2 Bose-Einstein Condensates

We numerically simulate the dynamics of a spin-2 Bose-Einstein condensate. We find that the initial phase plays an important role in the spin component oscillations. The spin mixing processes can fully cancel out due to quantum interference when taking some initial special phase. In all the spin mixing processes, the total spin is conversed. When the initial population is mainly occupied by a component with the maximal or minimal magnetic quantum number, the oscillations of spin components cannot happen due to the total spin conversation. The presence of quadratic Zeeman energy terms suppresses some spin mixing processes so that the oscillations of spin components are suppressed in some initial spin configuration. However, the linear Zeeman energy terms have no effects on the spin mixing processes.     

Chaplygin gas quantum universe in the presence of the cosmological constant

We present a Chaplygin gas Friedmann-Robertson-Walker quantum cosmological model in the presence of the cosmological constant. We apply the Schutz’s variational formalism to recover the notion of time, and this gives rise to Wheeler-DeWitt equation for the scale factor. We study the early and late time universes and show that the presence of the Chaplygin gas leads to an effective positive cosmological constant for the late times. This suggests the possibility of changing the sign of the effective cosmological constant during the transition from the early times to the late times. For the case of an effective negative cosmological constant for both epoches, we solve the resulting Wheeler-DeWitt equation using the Spectral Method and find the eigenvalues and eigenfunctions for positive, zero, and negative constant spatial curvatures. Then, we use the eigenfunctions in order to construct wave packets for each case and obtain the time-dependent expectation value of the scale factors, which are found to oscillate between finite maximum and minimum values. Since the expectation value of the scale factors never tend to the singular point, we have an initial indication that this model may not have singularities at the quantum level.     

Atomic dynamics in the mode－mode competition system

The atomic dynamical properties in the system with competing k-photon and l-photon transitions are studied fully by means of quantum theory. We discuss the influences of the mode－mode competition, the relative competing strengths of the atom and the two-mode field, and the initial state of the system on the atomic dynamics. We show that the presence of the mode－mode competition can result in quite a periodical collapses-revivals of the atomic inversion and the increase of the initial photons of the system can lead to the collapse－revival phenomenon and prolong the revival time of the atomic inversion.     

Internal mode mechanism for collective energy transport in extended systems

We study directed energy transport in homogeneous nonlinear extended systems in the presence of homogeneous ac forces and dissipation. We show that the mechanism responsible for unidirectional motion of topological excitations is the coupling of their internal and translation degrees of freedom. Our results lead to a selection rule for the existence of such motion based on resonances that explain earlier symmetry analysis of this phenomenon. The direction of motion is found to depend both on the initial and the relative phases of the two harmonic drivings, even in the presence of noise.     

Stability of an impulsively accelerated density interface in magnetohydrodynamics

In the framework of ideal incompressible magnetohydrodynamics, we examine the stability of an impulsively accelerated, sinusoidally perturbed density interface in the presence of a magnetic field that is parallel to the acceleration. This is accomplished by analytically solving the linearized initial value problem, which is a model for the Richtmyer-Meshkov instability. We find that the initial growth rate of the interface is unaffected by the presence of a magnetic field, but for a finite magnetic field the interface amplitude asymptotes to a constant value. Thus the instability of the interface is suppressed. The interface behavior from the analytical solution is compared to the results of both linearized and nonlinear compressible numerical simulations.     

Superfluidlike motion of vortices in light condensates

We demonstrate, through numerical simulations, the generation of stable vortex lattices in light condensates. This can be achieved by propagating several concentric laser beams with nested vortices of different topological charges in an optical material with a cubic-quintic nonlinearity. We have considered several initial conditions, and in all the cases the net topological charges of the resulting lattice is equal to the topological charge of the initial outer vortex. The lattice exhibits rotation similar to vortex motion in superfluids. These vortex arrays could be used to implement all-optical photonic crystal fibers. Our results also apply to Bose-Einstein condensates in the presence of three-body elastic interactions.     

Squeezing Effects of a Mesoscopic Dissipative Coupled Circuit

We study the quantum effect of a mesoscopic dissipative-coupled RLC circuit of the capacitances. We find that if the quantum dissipative system is in the vacuum state at the initial time, it will evolve to a squeezed coherent state under the effect of an external pulse source because of the presence of the coupling and damping.     

Pancharatnam and total phases for one-dimensional photonic band gaps

We study the time evolution of the total and Pancharatnam phase of four-level atoms in the presence of a one-dimensional photonic-band-gap material. We obtain analytical and numerical results under certain parametric conditions and analyze the effect of a Kerr-like medium and the detuning parameter on the dynamics of the Pancharatnam phase for the initial atomic position. We observe an interesting feature of the Pancharatnam phase for the one-dimensional photonic-band-gap material.