34 research outputs found
Non-Gibbs states on a Bose-Hubbard lattice
We study the equilibrium properties of the repulsive quantum Bose-Hubbard
model at high temperatures in arbitrary dimensions, with and without disorder.
In its microcanonical setting the model conserves energy and particle number.
The microcanonical dynamics is characterized by a pair of two densities: energy
density and particle number density . The macrocanonical Gibbs
distribution also depends on two parameters: the inverse nonnegative
temperature and the chemical potential . We prove the existence of
non-Gibbs states, that is, pairs which cannot be mapped onto
. The separation line in the density control parameter space
between Gibbs and non-Gibbs states corresponds to
infinite temperature . The non-Gibbs phase cannot be cured into a
Gibbs one within the standard Gibbs formalism using negative temperatures.Comment: 8 pages, 1 figure, misprints correcte
Approximate expression for the dynamic structure factor in the Lieb-Liniger model
Recently, Imambekov and Glazman [Phys. Rev. Lett. 100, 206805 (2008)] showed
that the dynamic structure factor (DSF) of the 1D Bose gas demonstrates
power-law behaviour along the limiting dispersion curve of the collective modes
and calculated the corresponding exponents exactly. Combining these recent
results with a previously obtained strong-coupling expansion we present an
interpolation formula for the DSF of the 1D Bose gas. The obtained expression
is further consistent with exact low energy exponents from Luttinger liquid
theory and shows nice agreement with recent numerical results.Comment: 4 pages, 3 figure
Friction and diffusion of matter-wave bright solitons
We consider the motion of a matter-wave bright soliton under the influence of
a cloud of thermal particles. In the ideal one-dimensional system, the
scattering process of the quasiparticles with the soliton is reflectionless,
however, the quasiparticles acquire a phase shift. In the realistic system of a
Bose-Einstein condensate confined in a tight waveguide trap, the transverse
degrees of freedom generate an extra but small nonlinearity in the system which
gives rise to finite reflection and leads to dissipative motion of the soliton.
We calculate the velocity and temperature-dependent frictional force and
diffusion coefficient of a matter wave bright soliton immersed in a thermal
cloud
Decay of superfluid currents in the interacting one-dimensional Bose gas
We examine the superfluid properties of a 1D Bose gas in a ring trap based on
the model of Lieb and Liniger. While the 1D Bose gas has nonclassical
rotational inertia and exhibits quantization of velocities, the metastability
of currents depends sensitively on the strength of interactions in the gas: the
stronger the interactions, the faster the current decays. It is shown that the
Landau critical velocity is zero in the thermodynamic limit due to the first
supercurrent state, which has zero energy and finite probability of excitation.
We calculate the energy dissipation rate of ring currents in the presence of
weak defects, which should be observable on experimental time scales.Comment: 5 pages, 4 figure
The Dynamic Structure Factor of the 1D Bose Gas near the Tonks-Girardeau Limit
While the 1D Bose gas appears to exhibit superfluid response under certain
conditions, it fails the Landau criterion according to the elementary
excitation spectrum calculated by Lieb. The apparent riddle is solved by
calculating the dynamic structure factor of the Lieb-Liniger 1D Bose gas. A
pseudopotential Hamiltonian in the fermionic representation is used to derive a
Hartree-Fock operator, which turns out to be well-behaved and local. The
Random-Phase approximation for the dynamic structure factor based on this
derivation is calculated analytically and is expected to be valid at least up
to first order in , where is the dimensionless interaction
strength of the model. The dynamic structure factor in this approximation
clearly indicates a crossover behavior from the non-superfluid Tonks to the
superfluid weakly-interacting regime, which should be observable by Bragg
scattering in current experiments.Comment: 4 pages, 2 figures misprints in formulas correcte
Polarizability and dynamic structure factor of the one-dimensional Bose gas near the Tonks-Girardeau limit at finite temperatures
Correlation functions related to the dynamic density response of the
one-dimensional Bose gas in the model of Lieb and Liniger are calculated. An
exact Bose-Fermi mapping is used to work in a fermionic representation with a
pseudopotential Hamiltonian. The Hartree-Fock and generalized random phase
approximations are derived and the dynamic polarizability is calculated. The
results are valid to first order in 1/\gamma where \gamma is Lieb-Liniger
coupling parameter. Approximations for the dynamic and static structure factor
at finite temperature are presented. The results preclude superfluidity at any
finite temperature in the large-\gamma regime due to the Landau criterion. Due
to the exact Bose-Fermi duality, the results apply for spinless fermions with
weak p-wave interactions as well as for strongly interacting bosons.Comment: 13 pages, 5 figures, the journal versio