Density fluctuations in a very elongated Bose gas : crossover from weakly to strongly interacing regimes and 1D-3D dimensionnal crossover

Nick P. Proukakis

Isabelle Bouchoule, Julien Armijo, T. Jacqmin +1 more

In this seminar, we present results obtained on our atom-chip setup. Measuring in situ density fluctuations in very elongated gases we probe the physics of 1D Bose gases with repulsive interactions. We investigate the crossover from weakly to strongly interacting gases. For weakly interacting gases, we probed the transition from 1D physics to 3D physics.

Isabelle Bouchoule, Julien Armijo, T. Jacqmin +1 more

By measuring the density fluctuations in a highly elongated weakly interacting Bose gas, we observe and quantify the transition from the ideal gas to a quasi-condensate regime throughout the dimensional crossover from a purely 1D to an almost 3D gas. We show that that the entire transition region and the dimensional crossover are described surprisingly well by the modified Yang-Yang model. Furthermore, we find that at low temperatures the linear density at the quasi-condensate transition scales according to an interaction-driven scenario of a longitudinally uniform 1D Bose gas, whereas at high temperatures it scales according to the degeneracy-driven critical scenario of transverse condensation of a 3D ideal gas. We also perform measurements of the third moment of atom number fluctuations. We find a positive skewness of the atom number distribution in the ideal gas regime and a reduced skewness compatible with zero in the quasi-condensate regime. For our parameters, the third moment is a thermodynamic quantity whose measurement constitutes a sensitive test of the equation of state and our results are in agreement with a modified Yang-Yang thermodynamic prediction. Moreover, we show that the measured skewness reveals the presence of true three body correlations in the system.

J. Lauwers, André F. Verbeure

E.L. Hazlett, Li-Chung Ha, Logan W. Clark +1 more

Julien Armijo, T. Jacqmin, Karen V. Kheruntsyan +1 more

By measuring the density fluctuations in a highly elongated weakly interacting Bose gas, we observe and quantify the transition from the ideal gas to a quasi-condensate regime throughout the dimensional crossover from a purely 1D to an almost 3D gas. We show that that the entire transition region and the dimensional crossover are described surprisingly well by the modified Yang-Yang model. Furthermore, we find that at low temperatures the linear density at the quasi-condensate transition scales according to an interaction-driven scenario of a longitudinally uniform 1D Bose gas, whereas at high temperatures it scales according to the degeneracy-driven critical scenario of transverse condensation of a 3D ideal gas.