36 research outputs found
Emergence of a new pair-coherent phase in many-body quenches of repulsive bosons
We investigate the dynamical mode population statistics and associated first-
and second-order coherence of an interacting bosonic two-mode model when the
pair-exchange coupling is quenched from negative to positive values. It is
shown that for moderately rapid second-order transitions, a new pair-coherent
phase emerges on the positive coupling side in an excited state, which is not
fragmented as the ground-state single-particle density matrix would prescribe
it to be.Comment: 4 pages of RevTex4-1, 4 figures; Rapid Communication in Physical
Review
Dynamical mean-field theory for bosons
We discuss the recently developed bosonic dynamical mean-field (B-DMFT)
framework, which maps a bosonic lattice model onto the selfconsistent solution
of a bosonic impurity model with coupling to a reservoir of normal and
condensed bosons. The effective impurity action is derived in several ways: (i)
as an approximation to the kinetic energy functional of the lattice problem,
(ii) using a cavity approach, and (iii) by using an effective medium approach
based on adding a one-loop correction to the selfconsistently defined
condensate. To solve the impurity problem, we use a continuous-time Monte Carlo
algorithm based on a sampling of a perturbation expansion in the hybridization
functions and the condensate wave function. As applications of the formalism we
present finite temperature B-DMFT phase diagrams for the bosonic Hubbard model
on a 3d cubic and 2d square lattice, the condensate order parameter as a
function of chemical potential, critical exponents for the condensate, the
approach to the weakly interacting Bose gas regime for weak repulsions, and the
kinetic energy as a function of temperature.Comment: 26 pages, 19 figure
Unified picture of superfluidity: From Bogoliubov's approximation to Popov's hydrodynamic theory
Using a non-perturbative renormalization-group technique, we compute the
momentum and frequency dependence of the anomalous self-energy and the
one-particle spectral function of two-dimensional interacting bosons at zero
temperature. Below a characteristic momentum scale , where the Bogoliubov
approximation breaks down, the anomalous self-energy develops a square root
singularity and the Goldstone mode of the superfluid phase (Bogoliubov sound
mode) coexists with a continuum of excitations, in agreement with the
predictions of Popov's hydrodynamic theory. Thus our results provide a unified
picture of superfluidity in interacting boson systems and connect Bogoliubov's
theory (valid for momenta larger than ) to Popov's hydrodynamic approach.Comment: v2) 4 pages, 4 figures v3) Revised title + minor change
Phase separation of Bose-Einstein condensates
The zero-temperature system of two dilute overlapping Bose-Einstein
condensates is unstable against long wavelength excitations if the interaction
strength between the distinguishable bosons exceeds the geometric mean of the
like-boson interaction strengths. If the condensates attract each other, the
instability is similar to the instability of the negative scattering length
condensates. If the condensates repel, they separate spatially into condensates
of equal pressure. We estimate the boundary size, surface tension and energy of
the phase separated condensate system and we discuss the implications for
double condensates in atomic traps.Comment: 11 pages, 1 figur