Search results for "Einstein"
showing 10 items of 246 documents
Weakly Interacting Bose-Einstein Condensates under Rotation: Mean-Field versus Exact Solutions
2000
We consider a weakly-interacting, harmonically-trapped Bose-Einstein condensed gas under rotation and investigate the connection between the energies obtained from mean-field calculations and from exact diagonalizations in a subspace of degenerate states. From the latter we derive an approximation scheme valid in the thermodynamic limit of many particles. Mean-field results are shown to emerge as the correct leading-order approximation to exact calculations in the same subspace.
Singularity formation in the Gross-Pitaevskii equation and collapse in Bose-Einstein condensates
2004
We study the mechanisms of collapse of the condensate wave function in the Gross-Pitaevskii theory with attractive interparticle interaction. We reformulate the Gross-Pitaevskii equation as Newton's equations for a flux of particles, and introduce the collapsing fraction of particles. We assume that this collapsing fraction is expelled from the condensate due to dissipation. Using this hypothesis we analyze the dependence of the collapse behavior on the initial conditions. We find that, for a properly chosen negative scattering length, the remnant fraction of atoms becomes larger when the initial aspect ratio of the condensate is increased.
Ultracold atoms in optical lattices
2007
This article focuses on the characteristics and properties ultracold atoms in optical lattices.
Experiments on the dynamics of the Bose–Einstein condensate at finite temperatures
2009
This paper presents the results of our recent experiments on the finite-temperature Bose?Einstein condensate of 87Rb atoms in a magnetic trap, and is devoted to the study of the hydrodynamic properties and dynamics of an ultra-cold atomic gas near the critical temperature. Measurements of the aspect ratio of an expanding atomic cloud allow for verification of the condensate models and study of the interaction between condensed and non-condensed fractions of a finite-temperature sample.
Roton-roton crossover in strongly correlated dipolar Bose-nonstnon condensates
2011
We study the pair correlations and excitations of a dipolar Bose gas layer. The anisotropy of the dipole-dipole interaction allows us to tune the strength of pair correlations from strong to weak perpendicular and weak to strong parallel to the layer by increasing the perpendicular trap frequency. This change is accompanied by a roton-roton crossover in the spectrum of collective excitations, from a roton caused by the head-to-tail attraction of dipoles to a roton caused by the side-by-side repulsion, while there is no roton excitation for intermediate trap frequencies. We discuss the nature of these two kinds of rotons and the relation to instabilities of dipolar Bose gases. In both regime…
Probing number squeezing of ultracold atoms across the superfluid-Mott insulator transition.
2005
The evolution of on-site number fluctuations of ultracold atoms in optical lattices is experimentally investigated by monitoring the suppression of spin-changing collisions across the superfluid-Mott insulator transition. For low atom numbers, corresponding to an average filling factor close to unity, large on-site number fluctuations are necessary for spin-changing collisions to occur. The continuous suppression of spin-changing collisions is thus a direct evidence for the emergence of number-squeezed states. In the Mott insulator regime, we find that spin-changing collisions are suppressed until a threshold atom number, consistent with the number where a Mott plateau with doubly-occupied …
Nonequilibrium effective temperature of superfluid vortex tangle
2006
An effective nonequilibrium temperature in counterflow superfluid turbulence is proposed, as a parameter characterizing a canonical probability distribution function of vortex orientation, and relating the diffusion coefficient of vortex lines to the vortex friction through an Einstein relation.
Subdiffractive solitons in bose-einstein condensates
2005
We predict the disappearance of diffraction (the increase of the mass) of Bose-Einstein condensates in counter-moving periodic potentials. We demonstrate subdiffractive solitons (stable droplets of the condensate) in the vicinity of this zero diffraction point.
Finite boson and fermion systems under extreme rotation: edge reconstruction and vortex formation
2006
Vortices can form when finite quantal systems are set rotating. In the limit of small particle numbers, the vortex formation in a harmonically trapped fermion system, with repulsively interacting particles, shows similarities to the corresponding boson system, with vortices entering the rotating cloud for increasing rotation. For a larger number of fermions, N greater than or similar to 15, the fermion vortices compete and co-exist with (Chamon-Wen) edge-reconstructed ground states, forcing some ground states, as for example the central single vortex, into the spectrum of excited states. Experimentally, the fermion system could, for instance, be electrons in a semiconductor heterostructure,…
Exploring quantum matter with ultracold atoms in optical lattices
2005
Seventy years after Einstein's prediction, the seminal achievement of Bose–Einstein condensation in dilute atomic gases in 1995 has provided us with a new form of quantum matter. Such quantum matter can be described as a single giant matter wave. By loading it into an artificial periodic potential formed by laser light—a so-called optical lattice—it has become possible to probe matter far beyond the wave-like description. In a review of a series of experiments with ultracold quantum gases in optical lattices, we show that the granularity of the matter wave field, caused by the discreteness of atoms, gives rise to effects going beyond the simple single matter wave description. Bose–Einstein …