One-dimensional description of a Bose-Einstein condensate in a rotating closed-loop waveguide

We propose a general procedure for reducing the three-dimensional Schrodinger equation for atoms moving along a strongly confining atomic waveguide to an effective one-dimensional equation. This procedure is applied to the case of a rotating closed-loop waveguide. The possibility of including mean-field atomic interactions is presented. Application of the general theory to characterize a new concept of atomic waveguide based on optical tweezers is finally discussed

Macroscopic dynamics of a trapped Bose-Einstein condensate in the presence of 1D and 2D optical lattices

The hydrodynamic equations of superfluids for a weakly interacting Bose gas are generalized to include the effects of periodic optical potentials produced by stationary laser beams. The new equations are characterized by a renormalized interaction coupling constant and by an effective mass accounting for the inertia of the system along the laser direction. For large laser intensities the effective mass is directly related to the tunneling rate between two consecutive wells. The predictions for the frequencies of the collective modes of a condensate confined by a magnetic harmonic trap are discussed for both 1D and 2D optical lattices and compared with recent experimental data.Comment: 4 pages, 2 postscript figure

Observation of Spin Superfluidity in a Bose Gas Mixture

The spin dynamics of a harmonically trapped Bose-Einstein condensed binary mixture of sodium atoms is experimentally investigated at finite temperature. In the collisional regime the motion of the thermal component is shown to be damped because of spin drag, while the two condensates exhibit a counter flow oscillation without friction, thereby providing direct evidence for spin superfluidity. Results are also reported in the collisionless regime where the spin components of both the condensate and thermal part oscillate without damping, their relative motion being driven by a mean field effect. We also measure the static polarizability of the condensed and thermal parts and we find a large increase of the condensate polarizability with respect to the T=0 value, in agreement with the predictions of theory.Comment: 6 pages, 4 figures + Suppl. Mat. (2 pages, 1 figure

Nonlinear Dynamics of a Bose Condensed Gas

We investigate the dynamic behavior of a Bose-condensed gas of alkali atoms interacting with repulsive forces and confined in a magnetic trap at zero temperature. Using the Thomas-Fermi approximation, we rewrite the Gross-Pitaevskii equation in the form of the hydrodynamic equations of superfluids. We present solutions describing large amplitude oscillations of the atomic cloud as well as the expansion of the gas after switching off the trap. We compare our theoretical predictions with the recent experimental data obtained at Jila and MIT.Comment: 5 pages, REVTeX, 4 postscript figures, available also at http://anubis.science.unitn.it/~dalfovo/papers/papers.htm

Scissors mode and superfluidity of a trapped Bose-Einstein condensed gas

We investigate the oscillation of a dilute atomic gas generated by a sudden rotation of the confining trap (scissors mode). This oscillation reveals the effects of superfluidity exhibited by a Bose-Einstein condensate. The scissors mode is investigated also in a classical gas above T_c in various collisional regimes. The crucial difference with respect to the superfluid case arises from the occurence of low frequency components, which are responsible for the rigid value of the moment of inertia. Different experimental procedures to excite the scissors mode are discussed.Comment: 4 pages, 3 figure

Fermi Gases in Slowly Rotating Traps: Superfluid vs Collisional Hydrodynamics

The dynamic behavior of a Fermi gas confined in a deformed trap rotating at low angular velocity is investigated in the framework of hydrodynamic theory. The differences exhibited by a normal gas in the collisional regime and a superfluid are discussed. Special emphasis is given to the collective oscillations excited when the deformation of the rotating trap is suddenly removed or when the rotation is suddenly stopped. The presence of vorticity in the normal phase is shown to give rise to precession and beating phenomena which are absent in the superfluid phase.Comment: 4 pages, 2 figure

Moment of Inertia and Superfluidity of a Trapped Bose Gas

The temperature dependence of the moment of inertia of a dilute Bose gas confined in a harmonic trap is determined. Deviations from the rigid value, due to the occurrence of Bose-Einstein condensation, reveal the superfluid behaviour of the system. In the noninteracting gas these deviations become important at temperatures of the order of $T_c N^{-1/12}$. The role of interactions is also discussed.Comment: 10 pages, REVTEX, 1 figure attached as postscript fil

Quasi 2D Bose-Einstein condensation in an optical lattice

We study the phase transition of a gas of Rb atoms to quantum degeneracy in the combined potential of a harmonically confining magnetic trap and the periodic potential of an optical lattice. For high optical lattice potentials we observe a significant change in the temperature dependency of the population of the ground state of the system. The experimental results are explained by the subsequent formation of quasi 2D condensates in the single lattice sites.Comment: 7 pages (including 3 figures

Sensitive measurement of forces at micron scale using Bloch oscillations of ultracold atoms

We show that Bloch oscillations of ultracold fermionic atoms in the periodic potential of an optical lattice can be used for a sensitive measurement of forces at the micrometer length scale, e.g. in the vicinity of dielectric surface. In particular, the proposed approach allows to perform a local and direct measurement of the Casimir-Polder force which is, for realistic experimental parameters, as large as 10^-4 gravity

Hydrodynamic modes of a 1D trapped Bose gas

We consider two regimes where a trapped Bose gas behaves as a one-dimensional system. In the first one the Bose gas is microscopically described by 3D mean field theory, but the trap is so elongated that it behaves as a 1D gas with respect to low frequency collective modes. In the second regime we assume that the 1D gas is truly 1D and that it is properly described by the Lieb-Liniger model. In both regimes we find the frequency of the lowest compressional mode by solving the hydrodynamic equations. This is done by making use of a method which allows to find analytical or quasi-analytical solutions of these equations for a large class of models approaching very closely the actual equation of state of the Bose gas. We find an excellent agreement with the recent results of Menotti and Stringari obtained from a sum rule approach.Comment: 15 pages, revtex, 1 figure