arXiv subjects

Abdelaali Boudjemaa

Publications and source records attributed to Abdelaali Boudjemaa.

45 records · Page 3Linked to original sources

arXiv2016

Collective modes of a one-dimensional trapped Bose gas in the presence of the anomalous density

We study the collective modes of a one-dimensional harmonically trapped Bose-Einstein condensate in the presence of the anomalous density using the time-dependent Hartree-Fock-Bogoliubov theory. Within the hydrodynamic equations, we derive analytical expressions for the mode frequencies and the density fluctuations of the anomalous density which constitutes the minority component at very low temperature and feels an effective external potential exerted by the majority component, i.e., the condensate. On the other hand, we numerically examine the temperature dependence of the breathing mode oscillations of the condensate at finite temperature in the weak-coupling regime. At zero temperature, we compare our predictions with available experimental data, theoretical treatments, and Monte carlo simulations in all interaction regimes and the remaining hindrances are emphasized. We show that the anomalous correlations have a non-negligible role on the collective modes at both zero and finite temperatures.

cond-mat.quant-gas↗

arXiv2016

Many-soliton bound states in dispersion-managed optical fiber: Possibility of fiber-optic transmission of three bits per clock period

We study the stability and the dynamics of many-soliton molecules in dispersion-managed (DM) optical fibers with focus on five-and seven-soliton molecules by analytical and numerical means. In particular we calculate the binding force, pulse durations and equilibrium separations using a variational approach. Predicted pulse shapes are in good agreement with those found by numerical simulations of the underlying nonlinear Schrödinger equation. Within limitations soliton molecules with up to seven solitons possibly allow to encode three bits of data per clock period.

nlin.PS↗

arXiv2016

Properties of dipolar bosonic quantum gases at finite temperatures

The properties of ultracold quantum gases of bosons with dipole-dipole interaction is investigated at finite temperature in the frame of the representative ensembles theory. Self-consistent coupled equations of motion are derived for the condensate and the non-condensate components. Corrections due to the dipolar interaction to the condensate depletion, the anomalous density and thermodynamic quantities such as the ground state energy, the equation of state, the compressibility and the presure are calculated in the homogeneous case at both zero and finite temperatures. Effects of interaction and temperature on the structure factor are also discussed. Within the realm of the local density approximation, we generalize our results to the case of a trapped dipolar gas.

cond-mat.quant-gas↗

arXiv2016

Thermodynamics of a two-dimensional dipolar Bose gas with correlated disorder in the roton regime

We sudy the impact of a weak random potential with a Gaussian correlation function on the thermodynamics of a two-dimensional (2D) dipolar bosonic gas. Analytical expressions for the quantum depletion, anomalous density, the ground state energy, the equation of state and the sound velocity are derived in the roton regime within the framework of the Bogoliubov theory. Surprisingly, we find that the condensate depletion and the anomalous density are comparable. The structure factor and the superfluid fraction are also obtained analytically and numerically. We show that these quantities acquire dramatically modified profiles when the roton is close to zero yielding the transition to an unusual quantum state.

cond-mat.dis-nn↗

arXiv2015

Spontaneous formation of bright solitons in self-localized impurities in Bose-Einstein condensate

We study the formation of bright solitons in the impurity component of Bose-Einstein condensate (BEC)-impurity mixture by using the time-dependent Hartree-Fock-Bogoliubov theory. While we assume the boson-boson and impurity-boson interactions to be effectively repulsive, their character can be changed spontaneously from repulsive to attractive in the presence of strong anomalous correlations. In such a regime the impurity component becomes a system of effectively attractive atoms leading automatically to the generation of bright solitons. We find that this soliton decays at higher temperatures due to the dissipation induced by the impurity-host and host-host interactions. We show that after a sudden increase of the impurity-boson strength a train of bright solitons is produced and this can be interpreted in terms of the modulational instability (MI) of the time-dependent impurity wave function.

cond-mat.quant-gas↗

arXiv2015

Superfluidity and Bose-Einstein condensation in a dipolar Bose gas with weak disorder

We investigate the properties of a three-dimensional homogeneous dipolar Bose gas in a weak random potential with a Gaussian correlation function at finite temperature. Using the Bogoliubov theory (beyond the mean field), we calculate the superfluid and the condensate fractions in terms of the interaction strength on the one hand and in terms of the width and the strength of the disorder on the other. The influence of the disordered potential on the second order correlation function, the ground state energy and the chemical potential is also analyzed. We find that for fixed strength and correlation length of the disorder potential, the dipole-dipole interaction leads to modify both the condensate and the superfluid fractions. We show that for a strong disorder strength the condensed fraction becomes larger than the superfluid fraction. We discuss the effect of the trapping potential on a disordered dipolar Bose in the regime of large number of particles.

cond-mat.dis-nn↗

arXiv2015

Two-dimensional dipolar bosons with weak disorder

We consider two-dimensional dipolar bosonic gas with dipoles oriented perpendicularly to the plane in a weak random potential. We investigate analytically and numerically the condensate depletion, the one-body density-matrix, the ground state energy, the sound velocity and the superfluid fraction. Concentrating on the regime where a rotonlike excitation spectrum forms, our results show that the superfluidity disappears below a critical value of disorder strength yielding the transition to a non-trivial quantum regime.

cond-mat.dis-nn↗

arXiv2015

Dipolar Bose gas in a weak isotropic speckle disorder

We investigate the properties of a homogeneous dipolar Bose gas in a weak three-dimensional (3D) isotropic speckle disorder at finite temperature. By using the Bogoliubov theory (beyond the mean field), we calculate the condensate and the superfluid fractions as a function of density and strengths of disorder and interaction. The influence of disorder on the anomalous density, the chemical potential and the ground state energy is also analyzed. We show that the peculiar interplay of the DDI and weak disorder makes the superfluid fraction and sound velocity anisotropic.

cond-mat.dis-nn↗

arXiv2014

Theory of excitations of dipolar Bose-Einstein condensate at finite temperature

We present a systematic study of dilute three-dimensional dipolar Bose gas employing a finite temperature perturbation theory (beyond the mean field). We analyze in particular the behavior of the anomalous density, we find that this quantity has a finite value in the limit of weak interactions at both zero and finite temperatures. We show that the presence of the dipole-dipole interaction (DDI) enhances fluctuations, the second order correlation function and thermodynamic quantities such as the chemical potential, the ground state energy, the compressibility and the superfluid fraction. We identify the validity criterion of the small parameter of the theory for Bose-condensed dipolar gases.

cond-mat.quant-gas↗