The rapidly developing field of optomechanics aims at the combined control of optical and mechanical (solid-state or atomic) modes. In particular, laser cooled atoms have been used to exploit optomechanical coupling for self-organization in a variety
of schemes where the accessible length scales are constrained by a combination of pump modes and those associated to a second imposed axis, typically a cavity axis. Here, we consider a system with many spatial degrees of freedom around a single distinguished axis, in which two symmetries - rotations and translations in the plane orthogonal to the pump axis - are spontaneously broken. We observe the simultaneous spatial structuring of the density of a cold atomic cloud and an optical pump beam. The resulting patterns have hexagonal symmetry. The experiment demonstrates the manipulation of matter by opto-mechanical self-assembly with adjustable length scales and can be potentially extended to quantum degenerate gases.
We study experimentally and numerically the quasi-bidimensional transport of a $^{87}$Rb Bose-Einstein condensate launched with a velocity $v_0$ inside a disordered optical potential created by a speckle pattern. A time-of-flight analysis reveals a p
ronounced enhanced density peak in the backscattering direction $-v_0$, a feature reminiscent of coherent backscattering. Detailed numerical simulations indicate however that other effects also contribute to this enhancement, including a backscattering echo due to the position-momentum correlations of the initial wave packet.
We show that, for a near-resonant propagating beam, a large cloud of cold 87Rb atoms acts as a saturable Kerr medium and produces self-trapping of light. By side fluorescence imaging we monitor the transverse size of the beam and, depending on the si
gn of the laser detuning with respect to the atomic transition, we observe self-focusing or -defocusing, with the waist remaining stationary for an appropriate choice of parameters. We analyze our observations by using numerical simulations based on a simple 2-level atom model.
We present an investigation of the fast decompression of a three-dimensional (3D) Bose-Einstein condensate (BEC) at finite temperature using an engineered trajectory for the harmonic trapping potential. Taking advantage of the scaling invariance prop
erties of the time-dependent Gross-Pitaevskii equation, we exhibit a solution yielding a final state identical to that obtained through a perfectly adiabatic transformation, in a much shorter time. Experimentally, we perform a large trap decompression and displacement within a time comparable to the final radial trapping period. By simultaneously monitoring the BEC and the non-condensed fraction, we demonstrate that our specific trap trajectory is valid both for a quantum interacting many-body system and a classical ensemble of non-interacting particles.
