187 research outputs found
Scale Separation Scheme for Simulating Superfluid Turbulence: Kelvin-Wave Cascade
A Kolmogorov-type cascade of Kelvin waves--the distortion waves on vortex
lines--plays a key part in the relaxation of superfluid turbulence at low
temperatures. We propose an efficient numeric scheme for simulating the Kelvin
wave cascade on a single vortex line. The idea is likely to be generalizable
for a full-scale simulation of different regimes of superfluid turbulence. With
the new scheme, we are able to unambiguously resolve the cascade spectrum
exponent, and thus to settle the controversy between recent simulations [1] and
recently developed analytic theory [2].
[1] W.F. Vinen, M. Tsubota and A. Mitani, Phys. Rev. Lett. 91, 135301 (2003).
[2] E.V. Kozik and B.V. Svistunov, Phys. Rev. Lett. 92, 035301 (2004).Comment: 4 pages, RevTe
Comment on "Dispersive bottleneck delaying thermalization of turbulent Bose-Einstein Condensates" by Krstulovic and Brachet [arXiv:1007.4441]
We reveal the connection of the recent numerical observations of Krstulovic
and Brachet [arXiv:1007.4441] with the general theory of relaxation kinetics of
the strongly non-equilibrium Bose-Einstein condensates.Comment: comment on arXiv:1007.4441, published version, minor stylistic
change
Supercurrent Stability in a Quasi-1D Weakly Interacting Bose Gas
We discuss a possibility of observing superfluid phenomena in a quasi-1D
weakly interacting Bose gas at finite temperatures. The weakness of interaction
in combination with generic properties of 1D liquids can result in a situation
when relaxational time of supercurrent is essentially larger than the time of
experimental observation, and the behavior of the system is indistinguishable
from that of a genuine superfluid.Comment: Revtex, 4 pages, no figures; Submitted to Phys. Rev. A (Brief
Reports
Phase diagram and thermodynamics of the three-dimensional Bose-Hubbard model
We report results of quantum Monte Carlo simulations of the Bose-Hubbard
model in three dimensions. Critical parameters for the
superfluid-to-Mott-insulator transition are determined with significantly
higher accuracy than it has been done in the past. In particular, the position
of the critical point at filling factor n=1 is found to be at (U/t)_c =
29.34(2), and the insulating gap Delta is measured with accuracy of a few
percent of the hopping amplitude t. We obtain the effective mass of particle
and hole excitations in the insulating state--with explicit demonstration of
the emerging particle-hole symmetry and relativistic dispersion law at the
transition tip--along with the sound velocity in the strongly correlated
superfluid phase. These parameters are the necessary ingredients to perform
analytic estimates of the low temperature (T << Delta) thermodynamics in
macroscopic samples. We present accurate thermodynamic curves, including these
for specific heat and entropy, for typical insulating (U/t=40) and superfluid
(t/U=0.0385) phases. Our data can serve as a basis for accurate experimental
thermometry, and a guide for appropriate initial conditions if one attempts to
use interacting bosons in quantum information processing.Comment: 11 pages, 13 figure
Criticality in Trapped Atomic Systems
We discuss generic limits posed by the trap in atomic systems on the accurate
determination of critical parameters for second-order phase transitions, from
which we deduce optimal protocols to extract them. We show that under current
experimental conditions the in-situ density profiles are barely suitable for an
accurate study of critical points in the strongly correlated regime. Contrary
to recent claims, the proper analysis of time-of-fight images yields critical
parameters accurately.Comment: 4 pages, 3 figures; added reference
Comment on "Symmetries and Interaction Coefficients of Kelvin waves" [arXiv:1005.4575] by Lebedev and L'vov
We comment on the claim by Lebedev and L'vov [arXiv:1005.4575] that the
symmetry with respect to a tilt of a quantized vortex line does not yet
prohibit coupling between Kelvin waves and the large-scale slope of the line.
Ironically, the counterexample of an effective scattering vertex in the local
induction approximation (LIA) attempted by Lebedev and L'vov invalidates their
logic all by itself being a notoriously known example of how symmetries impose
stringent constraints on kelvon kinetics---not only the coupling in question
but the kinetics in general are absent within LIA. We further explain that the
mistake arises from confusing symmetry properties of a specific mathematical
representation in terms of the canonical vortex position field w(z) = x(z) +
iy(z), which explicitly breaks the tilt symmetry due to an arbitrary choice of
the z-axis, with those of the real physical system recovered in final
expressions.Comment: comment on arXiv:1005.4575, version accepted in JLTP with minimal
changes: abstract adde
Comment on "Direct Mapping of the Finite Temperature Phase Diagram of Strongly Correlated Quantum Models" by Q. Zhou, Y. Kato, N. Kawashima, and N. Trivedi, Phys. Rev. Lett. 103, 085701 (2009)
In their Letter, Zhou, Kato, Kawashima, and Trivedi claim that
finite-temperature critical points of strongly correlated quantum models
emulated by optical lattice experiments can generically be deduced from kinks
in the derivative of the density profile of atoms in the trap with respect to
the external potential, . In this comment we demonstrate
that the authors failed to achieve their goal: to show that under realistic
experimental conditions critical densities can be extracted from
density profiles with controllable accuracy.Comment: 1 page, 1 figur
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