We investigate the particle-number fluctuations of condensate due to collective excitations for trapped two-dimensional (2D) and quasi-2D Bose gases at low temperature. We show that the fluctuations of the condensate are proportional to the square of the total particle number of the system. For a quasi-2D Bose gas the fluctuations are also proportional to the square root of the trapping frequen...

Influence of the damping on collective oscillations of a one-dimensional trapped Bose gas in the mean field regime has been studied. Using the phenomenological damping approach developed by L.P. Pitaevskii, modified variational equations for the parameters of the condensate wave function is derived. Analytical expressions for the condensate parameters in equilibrium state have been obtained. Bi...

We study the quantum and the mean-field Gross-Pitaevskii (GP) dynamics of a Bose-Einstein condensate gas confined in a toroidal trap. According to GP, if the interatomic interaction is attractive, the rotational states of the system can be dynamically stable or unstable depending on the strength of the mean-field energy. The full quantum analysis, however, reveals that the condensate is always ...

We report on the single-atom-resolved measurement of the distribution of momenta ℏk in a weakly interacting Bose gas after a 330 ms time of flight. We investigate it for various temperatures and clearly separate two contributions to the depletion of the condensate by their k dependence. The first one is the thermal depletion. The second contribution falls off as k^{-4}, and its magnitude increa...

We study the temperature evolution of the 〈q̄q〉 condensate below the chiral phase transition. The hadronic gas is described using a virial expansion within Generalized Chiral Perturbation Theory. In such way, we can implement both the large or small chiral condensate scenarios and analyze the condensate dependence on the values of the lightest quark masses. PACS:11.30.Rd, 12.39.Fe, 21.65.+f, 51....

We study a Bose-Einstein condensate of a dilute gas with dipolar interactions, at finite temperature, using the Hartree-Fock-Bogoliubov theory within the Popov approximation. An additional approximation involving the dipolar exchange interaction is made to facilitate the computation. We calculate the temperature dependence of the condensate fraction of a condensate confined in a cylindrically s...

We study theoretically superfluidity in a driven-dissipative Bose gas out of thermal equilibrium, and discuss the relation with conventional superfluids. We show how the superfluid behavior is characterized by a dramatic increase in the lifetime of a quantized vortex and point out the influence of the spatial geometry of the condensate. We apply our study to a condensate of polaritons in a semi...

Collective excitations of a dilute Bose gas were probed above and below the Bose-Einstein condensation temperature. The temperature dependencies of the frequency and damping rates of condensate oscillations indicate significant interactions between the condensate and the thermal cloud. Hydrodynamic oscillations of the thermal cloud analogous to first sound were observed. An outof-phase dipolar ...