No Arabic abstract
We use the T-matrix approach for studying highly polarized homogeneous Fermi gases in one dimension with repulsive or attractive contact interactions. Using this approach, we compute ground state energies and values for the contact parameter that show excellent agreement with exact and other numerical methods at zero temperature, even in the strongly interacting regime. Furthermore, we derive an exact expression for the value of the contact parameter in one dimension at zero temperature. The model is then extended and used for studying the temperature dependence of ground state energies and the contact parameter.
Quantum Monte Carlo (QMC) techniques are used to provide an approximation-free investigation of the phases of the one-dimensional attractive Hubbard Hamiltonian in the presence of population imbalance. The temperature at which the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase is destroyed by thermal fluctuations is determined as a function of the polarization. It is shown that the presence of a confining potential does not dramatically alter the FFLO regime, and that recent experiments on trapped atomic gases likely lie just within the stable temperature range.
We analyze phase interferometry realized with a bosonic Josephson junction made of trapped dilute and ultracold atoms. By using a suitable phase sensitivity indicator we study the zero temperature junction states useful to achieve sub shot-noise precisions. Sub shot-noise phase shift sensitivities can be reached even at finite temperature under a suitable choice of the junction state. We infer a scaling law in terms of the size system (that is, the number of particles) for the temperature at which the shot-noise limit is not overcome anymore
We present a study of how macroscopic flow can be produced in Bose-Einstein condensate confined in a racetrack potential by stirring with a wide rectangular barrier. This potential consists of two half-circle channels separated by straight channels of length $L$ and is a ring potential if $L=0$. We present the results of a large set of simulations where racetrack condensates stirred with a barrier under varying conditions of barrier height, stir speed, racetrack geometry, and temperature. We found that stirring was readily able to produce circulation in ring and non-ring geometries but that the exact amount of flow produced was complicated. We therefore also studied the mechanism by which flow was produced in the stirring process. We found that circulation was induced by the swap of a vortex/anti-vortex pair that was initially created by backflow of the condensate in the region of depressed density by the barrier. When the barrier strength reached a critical value a number of these vortex-swap events occurred in rapid succession so that flow speed of the circulation produced was enough to exceed the stir speed of the barrier. Flow that was initially localized in the vortices involved in the vortex swap was converted into macroscopic flow around the racetrack by pairs of disturbances each generated during the vortex swap. Each pair consisted of a vortex/anti-vortex pair moving in the anti-stir direction and a compression wave moving in the stir direction. This picture of the mechanism for making flow will enable the design of stirring schedules that create a desired amount of flow.
We scrutinize the hydrodynamic approach for calculating dynamical correlations in one-dimensional superfluids near integrability and calculate the characteristic time scale {tau} beyond which this approach is valid. For time scales shorter than {tau} hydrodynamics fails and we develop an approach based on kinetics of fermionic quasiparticles described as mobile impurities. New universal results for the dynamical structure factor relevant to experiments in ultracold atomic gases are obtained.
We develop a finite-temperature hydrodynamic approach for a harmonically trapped one-dimensional quasicondensate and apply it to describe the phenomenon of frequency doubling in the breathing-mode oscillations of its momentum distribution. The doubling here refers to the oscillation frequency relative to the oscillations of the real-space density distribution, invoked by a sudden confinement quench. We find that the frequency doubling is governed by the quench strength and the initial temperature, rather than by the crossover from the ideal Bose gas to the quasicondensate regime. The hydrodynamic predictions are supported by the results of numerical simulations based on a finite-temperature c-field approach, and extend the utility of the hydrodynamic theory for low-dimensional quantum gases to the description of finite-temperature systems and their dynamics in momentum space.