Localized states and interaction-induced delocalization in Bose gases with quenched disorder (original) (raw)
Spatial Dependence of Entropy in Trapped Ultracold Bose Gases
2009
We find a new physical regime in the trapped Bose-Hubbard Hamiltonian using time-evolving block decimation. Between Mott-insulating and superfluid phases, the latter induced by trap compression, a spatially self-organized state appears in which non-local entropy signals entanglement between spatially distant superfluid shells. We suggest a linear rather than harmonic potential as an ideal way to observe such a self-organized system. We also explore both quantum information and thermal entropies in the superfluid regime, finding that while the former follows the density closely the latter can be strongly manipulated with the mean field.
Effects of Interactions and Temperature in Disordered Ultra-Cold Bose Gases
Journal of Modern Physics, 2014
We simulate ultra-cold interacting Bosons in quasi-one-dimensional, incommensurate optical lattices. In the tight-binding limit, these lattices have pseudo-random on-site energies and thus can potentially lead to Anderson localization. We explore the parameter regimes that lead to Anderson localization and investigate the role of repulsive interactions, harmonic confinement and finite temperature. We find that interactions can obscure the exponential localization characteristic of Anderson localization, thus impeding the direct observation of this phenomenon when interactions are present.
Weakly interacting Bose gas in a random environment
Physical Review B, 2009
Zero temperature properties of a dilute weakly interacting d-dimensional Bose gas in a random potential are studied. We calculate geometrical and energetic characteristics of the localized state of a gas confined in a large box or in a harmonic trap. Different regimes of the localized state are found depending on the ratio of two characteristic length scales of the disorder, the Larkin length and the disorder correlation length. Repulsing bosons confined in a large box with average density n well below a critical value n c are trapped in deep potential wells of extension much smaller than distance between them. Tunneling between these wells is exponentially small. The ground state of such a gas is a random singlet with no long-range phase correlation For n > n c repulsion between particles overcomes the disorder and the gas transits from the localized to a coherent superfluid state. The critical density n c is calculated in terms of the disorder parameters and the interaction strength. For atoms in traps four different regimes are found, only one of it is superfluid. The theory is extended to lower (1 and 2) dimensions. Its quantitative predictions can be checked in experiments with ultracold atomic gases and other Bose-systems.
Superfluidity and phase transitions in a resonant Bose gas
Annals of Physics, 2008
The atomic Bose gas is studied across a Feshbach resonance, mapping out its phase diagram, and computing its thermodynamics and excitation spectra. It is shown that such a degenerate gas admits two distinct atomic and molecular superfluid phases, with the latter ...
Disorder-induced phase control in superfluid Fermi-Bose mixtures
EPL (Europhysics Letters), 2009
We consider a mixture of a superfluid Fermi gas of ultracold atoms and a Bose-Einstein condensate of molecules possessing a continuous U (1) (relative phase) symmetry. We study the effects that a spatially random photo-associative-dissociative symmetry breaking coupling of the systems. Such coupling allows to control the relative phase between a superfluid order parameter of the Fermi system and the condensate wavefunction of molecules for temperatures below the BCS critical temperature. The presented mechanism of phase control belongs to the general class of disorderinduced order phenomena that rely on breaking of continuous symmetry.
Localization of Bose–Einstein Condensation by Disorder
Journal of Low Temperature Physics, 2006
Recent experiments suggest that Bose-Einstein condensation (BEC) in liquid 4 He can be localized when the liquid is confined in porous media. We demonstrate in a simple model of hard core bosons using Monte Carlo that the condensate can be separated into two parts. The two regions of condensate are separated by a region of uncondensed fluid that forms in response to a local attractive external potential. The aim is to illustrate that separated condensates, and therefore localized BEC, can be created in porous media.
Physical Review Letters, 2004
We investigate two-dimensional Bose system with the long range interactions in the presence of disorder. Formation of the bound states at strong impurity sites gives rise to an additional depletion of the superfluid density ns. We demonstrate the existence of the intermediate superfluid state where the condensate and localized bosons present simultaneously. We find that interactions suppress localization and that with the increase of the boson density the system experiences a sharp delocalization crossover into a state where all bosons are delocalized. We map our results onto the three dimensional system of vortices in type II superconductors in the presence of columnar defects; the intermediate superfluid state maps to an intermediate vortex liquid where vortex liquid neighbors pinned vortices. We predict the depinning transition within the vortex liquid and depinning induced vortex lattice/Bose glass melting.
Bose condensed gas in strong disorder potential with arbitrary correlation length
Applied Physics B, 2007
We study the properties of a dilute Bose condensed gas at zero temperature in the presence of a strong random potential with arbitrary correlation length. Starting from the underlying Gross-Pitaevskii equation, we use the random phase approximation in order to get a closed integral equation for the averaged density distribution which allows the determination of the condensate and the superfluid density. The obtained results generalize those of Huang and Meng (HM) to strong disorder. In particular, we find the critical value of the disorder strength, where the superfluid phase disappears by a first-order phase transition. We show how this critical value changes as a function of the correlation length.
Disorder-induced shift of condensation temperature for dilute trapped Bose gases
Europhysics Letters (EPL), 2006
We determine the leading shift of the Bose-Einstein condensation temperature for an ultracold dilute atomic gas in a harmonic trap due to weak disorder by treating both a Gaussian and a Lorentzian spatial correlation for the quenched disorder potential. Increasing the correlation length from values much smaller than the geometric mean of the trap scale and the mean particle distance to much larger values leads first to an increase of the positive shift to a maximum at this critical length scale and then to a decrease.
Order via Nonlinearity in Randomly Confined Bose Gases
International Journal of Bifurcation and Chaos, 2009
A Hartree–Fock mean-field theory of a weakly interacting Bose-gas in a quenched white noise disorder potential is presented. A direct continuous transition from the normal gas to a localized Bose-glass phase is found which has localized short-lived excitations with a gapless density of states and vanishing superfluid density. The critical temperature of this transition is as for an ideal gas undergoing Bose–Einstein condensation. Increasing the particle-number density a first-order transition from the localized state to a superfluid phase perturbed by disorder is found. At intermediate number densities both phases can coexist.