Anharmonic parametric excitation in optical lattices

We study both experimentally and theoretically the losses induced by parametric excitation in far-off-resonance optical lattices. The atoms confined in a 1D sinusoidal lattice present an excitation spectrum and dynamics substantially different from those expected for a harmonic potential. We develop a model based on the actual atomic Hamiltonian in the lattice and we introduce semiempirically a broadening of the width of lattice energy bands which can physically arise from inhomogeneities and fluctuations of the lattice, and also from atomic collisions. The position and strength of the parametric resonances and the evolution of the number of trapped atoms are satisfactorily described by our model.Comment: 7 pages, 5 figure

Motional Squashed States

We show that by using a feedback loop it is possible to reduce the fluctuations in one quadrature of the vibrational degree of freedom of a trapped ion below the quantum limit. The stationary state is not a proper squeezed state, but rather a ``squashed'' state, since the uncertainty in the orthogonal quadrature, which is larger than the standard quantum limit, is unaffected by the feedback action.Comment: 8 pages, 2 figures, to appear in the special Issue "Quantum Correlations and Fluctuations" of J. Opt.

All Optical Formation of an Atomic Bose-Einstein Condensate

We have created a Bose-Einstein condensate of 87Rb atoms directly in an optical trap. We employ a quasi-electrostatic dipole force trap formed by two crossed CO_2 laser beams. Loading directly from a sub-doppler laser-cooled cloud of atoms results in initial phase space densities of ~1/200. Evaporatively cooling through the BEC transition is achieved by lowering the power in the trapping beams over ~ 2 s. The resulting condensates are F=1 spinors with 3.5 x 10^4 atoms distributed between the m_F = (-1,0,1) states.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let

Evanescent-wave trapping and evaporative cooling of an atomic gas near two-dimensionality

A dense gas of cesium atoms at the crossover to two-dimensionality is prepared in a highly anisotropic surface trap that is realized with two evanescent light waves. Temperatures as low as 100nK are reached with 20.000 atoms at a phase-space density close to 0.1. The lowest quantum state in the tightly confined direction is populated by more than 60%. The system offers intriguing prospects for future experiments on degenerate quantum gases in two dimensions

Fictitious Magnetic Resonance by Quasi-Electrostatic Field

We propose a new kind of spin manipulation method using a {\it fictitious} magnetic field generated by a quasi-electrostatic field. The method can be applicable to every atom with electron spins and has distinct advantages of small photon scattering rate and local addressability. By using a $\rm{CO_2}$ laser as a quasi-electrostatic field, we have experimentally demonstrated the proposed method by observing the Rabi-oscillation of the ground state hyperfine spin F=1 of the cold $\rm{^{87}Rb}$ atoms and the Bose-Einstein condensate.Comment: 5 pages, 5 figure

Cooling atoms in an optical trap by selective parametric excitation

We demonstrate the possibility of energy-selective removal of cold atoms from a tight optical trap by means of parametric excitation of the trap vibrational modes. Taking advantage of the anharmonicity of the trap potential, we selectively remove the most energetic trapped atoms or excite those at the bottom of the trap by tuning the parametric modulation frequency. This process, which had been previously identified as a possible source of heating, also appears to be a robust way for forcing evaporative cooling in anharmonic traps.Comment: 5 pages, 5 figure

Nonperturbative and perturbative treatments of parametric heating in atom traps

We study the quantum description of parametric heating in harmonic potentials both nonperturbatively and perturbatively, having in mind atom traps. The first approach establishes an explicit connection between classical and quantum descriptions; it also gives analytic expressions for properties such as the width of fractional frequency parametric resonances. The second approach gives an alternative insight into the problem and can be directly extended to take into account nonlinear effects. This is specially important for shallow traps.Comment: 12 pages, 2 figure

Entanglement of atoms via cold controlled collisions

We show that by using cold controlled collisions between two atoms one can achieve conditional dynamics in moving trap potentials. We discuss implementing two qubit quantum--gates and efficient creation of highly entangled states of many atoms in optical lattices.Comment: 4 pages 3 figure

All-Optical Production of a Degenerate Fermi Gas

We achieve degeneracy in a mixture of the two lowest hyperfine states of $^6$Li by direct evaporation in a CO$_2$ laser trap, yielding the first all-optically produced degenerate Fermi gas. More than $10^5$ atoms are confined at temperatures below $4 \mu$K at full trap depth, where the Fermi temperature for each state is $8 \mu$K. This degenerate two-component mixture is ideal for exploring mechanisms of superconductivity ranging from Cooper pairing to Bose condensation of strongly bound pairs.Comment: 4 pgs RevTeX with 2 eps figs, to be published in Phys. Rev. Let