Simon Richard

Momentum Spectroscopy of 1D Phase Fluctuations in Bose-Einstein Condensates

We measure the axial momentum distribution of Bose-Einstein condensates with an aspect ratio of 152 using Bragg spectroscopy. We observe the Lorentzian momentum distribution characteristic of one-dimensional phase fluctuations. The temperature dependence of the width of this distribution provides a quantitative test of quasicondensate theory. In addition, we observe a condensate length consistent with the suppression of density fluctuations, even when phase fluctuations are large.

Critical temperature of a trapped, weakly interacting Bose gas.

We report on measurements of the critical temperature of a harmonically trapped, weakly interacting Bose gas as a function of atom number. Our results exclude ideal-gas behavior by more than two standard deviations, and agree quantitatively with mean-field theory. At our level of sensitivity, we find no additional shift due to critical fluctuations. In the course of this measurement, the onset of hydrodynamic expansion in the thermal component has been observed. Our thermometry method takes this feature into account.

Experimental study of the thermodynamics of an interacting trapped Bose-Einstein condensed gas

We have investigated experimentally the finite-temperature properties of a Bose-Einstein condensed cloud of

Momentum distribution and correlation function of quasicondensates in elongated traps

^{87}

Momentum Spectroscopy of Phase Fluctuations of an Elongated Bose-Einstein Condensate

Rb atoms in a harmonic trap. Focusing primarily on condensed fraction and expansion energy, we measure unambiguous deviations from ideal-gas thermodynamics, and obtain good agreement with a Hartree-Fock description of the mixed cloud. Our results offer for the first time clear evidence of the mutual interaction between the condensed and thermal components. To probe the low-temperature region unaccessible to the usual time-of-flight technique, we use coherent Bragg scattering as a filtering technique for the condensate. This allows us to separate spatially the condensed and normal components in time of flight, and to measure reliably temperatures as low as

Experimental study of coupling Bose–Einstein condensates into weakly non-trapping and trapping states

0.2 T_{\rm c}^0

Coherence length of an elongated condensate - A study by matter-wave interferometry

and thermal fractions as low as 10%.Finally, we observe evidence for the limitations of the usual image analysis procedure, pointing out to the need for a more elaborate model of the expansion of the mixed cloud.

One-dimensional behavior of elongated Bose-Einstein condensates

We calculate the spatial correlation function and momentum distribution of a phase-fluctuating, elongated three-dimensional condensate in a trap and in free expansion. We take the inhomogeneous density profile into account via a local-density approximation. We find an almost Lorentzian momentum distribution, in stark contrast with a Heisenberg-limited Thomas-Fermi condensate.

Production of CW and mode-locked atom lasers

We have measured the momentum distribution of an elongated BEC (aspect ratio of 152), for temperatures below the critical temperature. The corresponding coherence length is significantly smaller than the condensate length in a wide range of temperature, in quantitative agreement with theoretical predictions. The Lorentzian shape of the momentum spectrum supports the image of a phase fluctuating quasicondensate.

Coherent matter wave inertial sensors for precision measurements in space

Abstract We study the production of an atom laser from a Bose–Einstein condensate using radio-frequency out-coupling. Single frequency coupling from the Bose–Einstein condensate leads to unstable production of an atom laser due to the extreme sensitivity of this process to magnetic field fluctuations. The extent of this experimental instability is quantified. Stable, repeatable production of an atom laser is achieved by the frequency modulation of the coupling, which forms a frequency comb across the condensate. Different regimes of modulated coupling are discussed. In addition the coupling of atoms into a weakly trapping state is studied. The oscillation frequency of this state in the vertical direction is measured. Preliminary results indicating qualitative difference between condensate and thermal cloud coupling are presented.