Lattice supersolid phase of strongly correlated bosons in an optical cavity

We numerically simulate strongly correlated ultracold bosons coupled to a high-finesse cavity field, pumped by a laser beam in the transverse direction. Assuming a weak classical optical lattice added in the cavity direction, we model this system by a generalized Bose-Hubbard model, which is solved by means of bosonic dynamical mean-field theory. The complete phase diagram is established, which contains two novel self-organized quantum phases, lattice supersolid and checkerboard solid, in addition to conventional phases such as superfluid and Mott insulator. At finite but low temperature, thermal fluctuations are found to enhance the buildup of the self-organized phases. We demonstrate that cavity-mediated long-range interactions can give rise to stable lattice supersolid and checkerboard solid phases even in the regime of strong s-wave scattering. In the presence of a harmonic trap, we discuss coexistence of these self-organized phases, as relevant to experiments.Comment: 4 pages, 3 figure

Dynamic Kosterlitz-Thouless transition in 2D Bose mixtures of ultra-cold atoms

We propose a realistic experiment to demonstrate a dynamic Kosterlitz-Thouless transition in ultra-cold atomic gases in two dimensions. With a numerical implementation of the Truncated Wigner Approximation we simulate the time evolution of several correlation functions, which can be measured via matter wave interference. We demonstrate that the relaxational dynamics is well-described by a real-time renormalization group approach, and argue that these experiments can guide the development of a theoretical framework for the understanding of critical dynamics.Comment: 5 pages, 6 figure

Finite temperature analysis of a quasi2D dipolar gas

We present finite temperature analysis of a quasi2D dipolar gas. To do this, we use the Hartree Fock Bogoliubov method within the Popov approximation. This formalism is a set of non-local equations containing the dipole-dipole interaction and the condensate and thermal correlation functions, which are solved self-consistently. We detail the numerical method used to implement the scheme. We present density profiles for a finite temperature dipolar gas in quasi2D, and compare these results to a gas with zero-range interactions. Additionally, we analyze the excitation spectrum and study the impact of the thermal exchange

Observation of Bose-Einstein Condensation of Molecules

We have observed Bose-Einstein condensation of molecules. When a spin mixture of fermionic Li-6 atoms was evaporatively cooled in an optical dipole trap near a Feshbach resonance, the atomic gas was converted into Li_2 molecules. Below 600 nK, a Bose-Einstein condensate of up to 900,000 molecules was identified by the sudden onset of a bimodal density distribution. This condensate realizes the limit of tightly bound fermion pairs in the crossover between BCS superfluidity and Bose-Einstein condensation.Comment: 4 pages, 3 figure

Fifty-fold improvement in the number of quantum degenerate fermionic atoms

We have produced a quantum degenerate Li-6 Fermi gas with up to 7 x 10^7 atoms, an improvement by a factor of fifty over all previous experiments with degenerate Fermi gases. This was achieved by sympathetic cooling with bosonic Na-23 in the F=2, upper hyperfine ground state. We have also achieved Bose-Einstein condensation of F=2 sodium atoms by direct evaporation

Contrast Interferometry Using Bose-Einstein Condensates to Measure h/m and the Fine Structure Constant

The kinetic energy of an atom recoiling due to absorption of a photon was measured as a frequency using an interferometric technique called ``contrast interferometry''. Optical standing wave pulses were used as atom-optical elements to create a symmetric three-path interferometer with a Bose-Einstein condensate. The recoil phase accumulated in different paths was measured using a single-shot detection technique. The scheme allows for additional photon recoils within the interferometer and its symmetry suppresses several random and systematic errors including those from vibrations and ac Stark shifts. We have measured the photon recoil frequency of sodium to $7$ppm precision, using a simple realization of this scheme. Plausible extensions should yield a sufficient precision to bring within reach a ppb-level determination of $h/m$ and the fine structure constant $\alpha$

Collisional properties of ultracold K-Rb mixtures

We determine the inter-species s-wave triplet scattering length a3 for all K-Rb isotopic mixtures by measuring the cross-section for collisions between 41K and 87Rb in different temperature regimes. The positive value a3=+163(+57,-12)a0 ensures the stability of binary 41K-87Rb Bose-Einstein condensates. For the fermion-boson mixture 40K-87Rb we obtain a large and negative scattering length which implies an efficient sympathetic cooling of the fermionic species down to the degenerate regime.Comment: 4 pages, 4 figures; revised version (references added and small changes

Competition between Vortex Unbinding and Tunneling in an Optical Lattice

We study a system of two-dimensional Bose gases trapped in minima of a deep one-dimensional optical lattice potential. Increasing the tunneling amplitude between adjacent gases drives a deconfinement transition to a phase where coherence is established between neighboring two-dimensional gases. We compute the signature of this transition in the interference pattern of the system as well as in its rotational response, which provides a direct measurement of the superfluidity in the system.Comment: 4+ pages, 1 figur

Boson-fermion demixing in a cloud of lithium atoms in a pancake trap

We evaluate the equilibrium state of a mixture of 7Li and 6Li atoms with repulsive interactions, confined inside a pancake-shaped trap under conditions such that the thickness of the bosonic and fermionic clouds is approaching the values of the s-wave scattering lengths. In this regime the effective couplings depend on the axial confinement and full demixing can become observable by merely squeezing the trap, without enhancing the scattering lengths through recourse to a Feshbach resonance.Comment: 11 pages, 3 figures, to appear in Phys. Lett.