13,535 research outputs found
Coherence and Josephson oscillations between two tunnel-coupled one-dimensional atomic quasicondensates at finite temperature
We revisit the theory of tunnel-coupled atomic quasicondensates in
double-well elongated traps at finite temperatures. Using the
functional-integral approach, we calculate the relative-phase correlation
function beyond the harmonic limit of small fluctuations of the relative phase
and its conjugate relative-density variable. We show that the thermal
fluctuations of the relative phase between the two quasicondensates decrease
the frequency of Josephson oscillations and even wash out these oscillations
for small values of the tunnel coupling.Comment: revtex4, 4 figures (.eps
Multiple colliding electromagnetic pulses: a way to lower the threshold of pair production from vacuum
The scheme of simultaneous multiple pulse focusing on one spot naturally
arises from the structural features of projected new laser systems, such as ELI
and HiPER. It is shown that the multiple pulse configuration is beneficial for
observing pair production from vacuum under the action of sufficiently
strong electromagnetic fields. The field of the focused pulses is described
using a realistic three-dimensional model based on an exact solution of the
Maxwell equations. The pair production threshold in terms of
electromagnetic field energy can be substantially lowered if, instead of one or
even two colliding pulses, multiple pulses focused on one spot are used. The
multiple pulse interaction geometry gives rise to subwavelength field features
in the focal region. These features result in the production of extremely short
bunches.Comment: 10 pages, 4 figure
From Popov-Fedotov trick to universal fermionization
We show that Popov-Fedotov trick of mapping spin-1/2 lattice systems on
two-component fermions with imaginary chemical potential readily generalizes to
bosons with a fixed (but not limited) maximal site occupation number, as well
as to fermionic Hamiltonians with various constraints on the site Fock states.
In a general case, the mapping---fermionization---is on multi-component
fermions with many-body non-Hermitian interactions. Additionally, the
fermionization approach allows one to convert large many-body couplings into
single-particle energies, rendering the diagrammatic series free of large
expansion parameters; the latter is essential for the efficiency and
convergence of the diagrammatic Monte Carlo method.Comment: 4 pages, no figures (v2 contains some improvements; the most
important one is the generic complex chemical potential trick for
spins/bosons
Gapless Hartree-Fock-Bogoliubov Approximation for Bose Gases
A dilute Bose system with Bose-Einstein condensate is considered. It is shown
that the Hartree-Fock-Bogolubov approximation can be made both conserving as
well as gapless. This is achieved by taking into account all physical
normalization conditions, that is, the normalization condition for the
condensed particles and that for the total number of particles. Two Lagrange
multipliers, introduced for preserving these normalization conditions, make the
consideration completely self-consistent.Comment: Latex file, 22 pages, 2 figure
Fermion Pair Production From an Electric Field Varying in Two Dimensions
The Hamiltonian describing fermion pair production from an arbitrarily
time-varying electric field in two dimensions is studied using a
group-theoretic approach. We show that this Hamiltonian can be encompassed by
two, commuting SU(2) algebras, and that the two-dimensional problem can
therefore be reduced to two one-dimensional problems. We compare the group
structure for the two-dimensional problem with that previously derived for the
one-dimensional problem, and verify that the Schwinger result is obtained under
the appropriate conditions.Comment: Latex, 14 pages of text. Full postscript version available via the
worldwide web at http://nucth.physics.wisc.edu/ or by anonymous ftp from
ftp://nucth.physics.wisc.edu:/pub/preprints
Multidimensional Worldline Instantons
We extend the worldline instanton technique to compute the vacuum pair
production rate for spatially inhomogeneous electric background fields, with
the spatial inhomogeneity being genuinely two or three dimensional, both for
the magnitude and direction of the electric field. Other techniques, such as
WKB, have not been applied to such higher dimensional problems. Our method
exploits the instanton dominance of the worldline path integral expression for
the effective action.Comment: 22 pages, 13 figure
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