arXiv subjects

Tarik Yefsah

Publications and source records attributed to Tarik Yefsah.

22 records · Page 2Linked to original sources

arXiv2011

Exploring the thermodynamics of a two-dimensional Bose gas

Using \emph{in situ} measurements on a quasi two-dimensional, harmonically trapped $^{87}$Rb gas, we infer various equations of state for the equivalent homogeneous fluid. From the dependence of the total atom number and the central density of our clouds with the chemical potential and temperature, we obtain the equations of state for the pressure and the phase-space density. Then using the approximate scale invariance of this two-dimensional system, we determine the entropy per particle. We measure values as low as $0.06\,\kB$ in the strongly degenerate regime, which shows that a 2D Bose gas can constitute an efficient coolant for other quantum fluids. We also explain how to disentangle the various contributions (kinetic, potential, interaction) to the energy of the trapped gas using a time-of-flight method, from which we infer the reduction of density fluctuations in a non fully coherent cloud.

cond-mat.quant-gas↗

arXiv2010

The equilibrium state of a trapped two-dimensional Bose gas

We study experimentally and numerically the equilibrium density profiles of a trapped two-dimensional $^{87}$Rb Bose gas, and investigate the equation of state of the homogeneous system using the local density approximation. We find a clear discrepancy between in-situ measurements and Quantum Monte Carlo simulations, which we attribute to a non-linear variation of the optical density of the atomic cloud with its spatial density. However, good agreement between experiment and theory is recovered for the density profiles measured after time-of-flight, taking advantage of their self-similarity in a two-dimensional expansion.

cond-mat.quant-gas↗

arXiv2009

Practical scheme for a light-induced gauge field in an atomic Bose gas

We propose a scheme to generate an Abelian gauge field in an atomic gas using two crossed laser beams. If the internal atomic state follows adiabatically the eigenstates of the atom-laser interaction, Berry's phase gives rise to a vector potential that can nucleate vortices in a Bose gas. The present scheme operates even for a large detuning with respect to the atomic resonance, making it applicable to alkali-metal atoms without significant heating due to spontaneous emission. We test the validity of the adiabatic approximation by integrating the set of coupled Gross-Pitaevskii equations associated with the various internal atomic states, and we show that the steady state of the interacting gas indeed exhibits a vortex lattice, as expected from the adiabatic gauge field.

cond-mat.str-el↗

arXiv2008

Geometric potentials in quantum optics: A semi-classical interpretation

We propose a semi-classical interpretation of the geometric scalar and vector potentials that arise due to Berry's phase when an atom moves slowly in a light field. Starting from the full quantum Hamiltonian, we turn to a classical description of the atomic centre-of-mass motion while still treating the internal degrees of freedom as quantum variables. We show that the scalar potential can be identified as the kinetic energy of an atomic micro-motion caused by quantum fluctuations of the radiative force, and that the Lorentz-type force appears as a result of the motion-induced perturbation of the internal atomic state. For a specific configuration involving two counter-propagating Gaussian laser beams, we relate the geometric forces to the radiation pressure and dipole forces known from quantum optics. The simple physical pictures provided by the present analysis may help for the design and the implementation of novel geometric forces.

cond-mat.other↗