Showing papers by "Kazimierz Rzazewski published in 2000"

Bose-Einstein condensation with magnetic dipole-dipole forces

Abstract: Ground-state solutions in a dilute gas interacting via contact and magnetic dipole-dipole forces are investigated. To the best of our knowledge, it is the first example of studies of Bose-Einstein condensation in a system with realistic long-range interactions. We find that for the magnetic moment of, e.g., chromium $(6{\ensuremath{\mu}}_{B}),$ and a typical value of the scattering length, all solutions are stable and only differ in size from condensates without long-range interactions. By lowering the value of the scattering length we find a region of unstable solutions. In the neighborhood of this region, the ground-state wave functions show internal structures that we believe have not been seen before in condensates. Finally, we find an analytic estimate for the characteristic length appearing in these solutions.

Structure of binary Bose-Einstein condensates

Abstract: We identify all possible classes of solutions for two-component Bose-Einstein condensates (BECs) within the Thomas-Fermi (TF) approximation and check these results against numerical simulations of the coupled Gross-Pitaevskii equations (GPEs). We find that they can be divided into two general categories. The first class contains solutions with a region of overlap between the components. The other class consists of non-overlapping wavefunctions and also contains solutions that do not possess the symmetry of the trap. The chemical potential and average energy can be found for both classes within the TF approximation by solving a set of coupled algebraic equations representing the normalization conditions for each component. A ground state minimizing the energy (within both classes of states) is found for a given set of parameters characterizing the scattering length and confining potential. In the TF approximation, the ground state always shares the symmetry of the trap. However, a full numerical solution of the coupled GPEs, incorporating the kinetic energy of the BEC atoms, can sometimes select a broken-symmetry state as the ground state of the system. We also investigate effects of finite-range interactions on the structure of the ground state.

Quantum Anti-Zeno Effect

Abstract: We demonstrate that near-threshold decay processes may be accelerated by repeated measurements. Examples include near-threshold photodetachment of an electron from a negative ion, and spontaneous emission in a cavity close to the cutoff frequency or in a photon band-gap material.

Probing the statistical properties of Bose-Einstein condensates with light

Abstract: A scattering of short, weak, nonresonant laser pulses on a Bose-Einstein condensate is proposed as a tool for studying its statistical properties. We show in particular that the variance of the number of scattered photons may distinguish between the Poisson and microcanonical statistics.

Structure of binary Bose-Einstein condensates

Abstract: We identify all possible classes of solutions for two-component Bose-Einstein condensates (BECs) within the Thomas-Fermi (TF) approximation, and check these results against numerical simulations of the coupled Gross-Pitaevskii equations (GPEs). We find that they can be divided into two general categories. The first class contains solutions with a region of overlap between the components. The other class consists of non-overlapping wavefunctions, and contains also solutions that do not possess the symmetry of the trap. The chemical potential and average energy can be found for both classes within the TF approximation by solving a set of coupled algebraic equations representing the normalization conditions for each component. A ground state minimizing the energy (within both classes of the states) is found for a given set of parameters characterizing the scattering length and confining potential. In the TF approximation, the ground state always shares the symmetry of the trap. However, a full numerical solution of the coupled GPEs, incorporating the kinetic energy of the BEC atoms, can sometimes select a broken-symmetry state as the ground state of the system. We also investigate effects of finite-range interactions on the structure of the ground state.

Multi-mode description of an interacting Bose-Einstein condensate

Abstract: We study the equilibrium dynamics of a weakly interacting Bose-Einstein condensate trapped in a box. In our approach we use a semiclassical approximation similar to the description of a multi-mode laser. In dynamical equations derived from a full N-body quantum Hamiltonian we substitute all creation (and annihilation) operators (of a particle in a given box state) by appropriate c-number amplitudes. The set of nonlinear equations obtained in this way is solved numerically. We show that on the time scale of a few miliseconds the system exhibits relaxation - reaches an equilibrium with populations of different eigenstates fluctuating around their mean values.

Probe-field reflection on a plasma surface driven by a strong electromagnetic field

Abstract: We develop a theoretical approach to characterize the dynamics of a plasma surface irradiated by a high-intensity electromagnetic wave. The method is based on the analysis of the harmonic content in the reflection of a probe field, which is aimed at the plasma simultaneously with the strong field. In particular, a explicit formula for the angles of reflection of these harmonics is derived, showing a particular distribution directly related to the frequency of oscillation of the vacuum-plasma interface. Also, a system of equations for the reflected field amplitudes is formulated, and solved numerically in some particular cases. The experimental implementation of this scheme would provide a direct test of the so-called moving mirror models, which presently provide a basis for the understanding of the intense field-plasma interaction.

Finite temperature oscillations of a Bose-Einstein condensate in a two-gas model

Abstract: The temperature dependence of the frequencies of a Bose-Einstein condensate obtained in experiment has not been fully understood theoretically. In this paper we present a simplified version of a two-gas model. A numerically-found ground state of the system is used for the small-oscillations analysis. In the case of spherical symmetry a full spectrum of frequencies is found for low orbital quantum numbers. Avoided crossings that appear in the spectrum might be the reason for experimentally observed frequency shifts.