Quantum Phase Transitions in Cold Atoms and Low Temperature Solids

David C. McKay, Matt White, Matthew Pasienski +1 more

We have observed a metallic-like state, which persists to the zerotemperature limit, in a 3D Bose-Hubbard system of ultra-cold atoms trapped in an optical lattice. The damping rate of atomic motion— the analog of electrical resistance in a solid—in the confining parabolic potential fits well to a model that includes finite damping at zero temperature. The low-temperature behavior is consistent with the theory of quantum tunneling of phase slips, while at higher temperatures a cross-over consistent with the transition between quantum tunneling and thermal activation of phase slips is evident. The existence of a metallic phase in a bosonic system may have implications for the unusual dissipative phases apparent in solid-state superconducting films. The ground state of a system of bosons is predicted to be either superconducting or insulating (1). However, experiments on superconducting films have shown that a dissipative phase can exist to the lowest temperatures attainable. For example, experiments on

Hans Peter Büchler

Anatoli Polkovnikov

Masatoshi Kajita

As an introduction, the states of atoms and molecules are introduced. At room temperature, gaseous atoms and molecules move very fast. We imagine that the gaseous phase is transformed to liquid or solid phase by cooling, but it is possible only with high density of atoms and molecules. With low densities, atoms and molecules also stay in the gaseous state at low temperature. Research using cold atoms and molecules, trapped by electric or magnetic field, give important information to develop new physics.

Brent T. Fultz

Dmitry Solenov, Dmitry Mozyrsky

We study the kinetics of the first order phase separation transition in boson-fermion cold-atom mixtures. At sufficiently low temperatures such a transition is driven by quantum fluctuations responsible for the formation of critical nuclei of a stable phase. Based on a microscopic description of interacting boson-fermion mixtures we derive an effective action for the critical droplet and obtain an asymptotic expression for the nucleation rate in the vicinity of the phase transition and near the spinodal instability of the mixed phase. We also discuss effects of dissipation which play a dominant role close to the transition point, and identify the regimes where quantum nucleation can be experimentally observed in cold-atom systems.