861 research outputs found
Domain wall dynamics in a two-component Bose-Mott insulator
We model the dynamics of two species of bosonic atoms trapped in an optical
lattice within the Mott regime by mapping the system onto a spin model. A field
gradient breaks the cloud into two domains. We study how the domain wall
evolves under adiabatic and diabatic changes of this gradient. We determine the
timescales for adiabaticity, and study how temperature evolves for slow ramps.
We show that after large, sudden changes of the field gradient, the system does
not equilibrate on typical experimental timescales. We find interesting spin
dynamics even when the initial temperature is large compared to the
super-exchange energy. We discuss the implication of our results for
experiments wishing to use such a two-component system for thermometry, or as
part of a cooling scheme.Comment: 6 pages, 5 figures Minor typographical errors corrected. Figure
labels changed. Added concluding statement
Evolution of the Pseudogap in a polarized Fermi gas
We calculate the single particle spectral density of a normal
(non-superfluid) two component gas of fermions in the BCS-BEC crossover within
a T-matrix approximation. We review how non-condensed pairs lead to a spectral
density reminiscent of the ordered state, and explore how a gap-like feature in
the spectrum evolves as one changes the polarization of the gas. As the gas is
polarized we find that this pseudogap becomes more diffuse and moves away from
the Fermi level, reflecting the fact that fewer pairs are present but that they
still play an important role in the excitations.Comment: 7 pages, 6 figure
Complex Time Solutions with Nontrivial Topology and Multi Particle Scattering in Yang-Mills Theory
A classical solution to the Yang-Mills theory is given a new semiclassical
interpretation in terms of particle scattering. It solves the complex time
boundary value problem, which arises in the semiclassical approximation to a
multi particle transition probability in the one-instanton sector at fixed
energy. The imaginary part of the action of the solution on the complex time
contour and its topological charge obey the same relation as the self-dual
Euclidean configurations. Hence the solution is relevant for the problem of
tunneling with fermion number violation in the electroweak theory. It describes
transitions from an initial state with a smaller number of particles to a final
state with a larger number of particles. The implications of these results for
multi particle production in the electroweak theory are also discussed.Comment: 10 pgs. (LaTeX), JHU-TIPAC-93001
Quantum Scattering from Classical Field Theory
We show that scattering amplitudes between initial wave packet states and
certain coherent final states can be computed in a systematic weak coupling
expansion about classical solutions satisfying initial value conditions. The
initial value conditions are such as to make the solution of the classical
field equations amenable to numerical methods. We propose a practical procedure
for computing classical solutions which contribute to high energy two particle
scattering amplitudes. We consider in this regard the implications of a recent
numerical simulation in classical SU(2) Yang-Mills theory for multiparticle
scattering in quantum gauge theories and speculate on its generalization to
electroweak theory. The generalization of our results to complex trajectories
allows its application to it any wave packet to coherent state transition.
Finally, we discuss the relevance of these results to the issues of baryon
number violation and multiparticle scattering at high energies.Comment: 20 pages, JHU-TIPAC-940003, HUTP-A0/007, Latex, uses prepictex.tex,
pictex.tex, and postpictex.tex (available by ftp from [email protected]) to
produce figure
Exact Parent Hamiltonian for the Quantum Hall States in a Optical Lattice
We study lattice models of charged particles in uniform magnetic fields. We
show how longer range hopping can be engineered to produce a massively
degenerate manifold of single-particle ground states with wavefunctions
identical to those making up the lowest Landau level of continuum electrons in
a magnetic field. We find that in the presence of local interactions, and at
the appropriate filling factors, Laughlin's fractional quantum Hall
wavefunction is an exact many-body ground state of our lattice model. The
hopping matrix elements in our model fall off as a Gaussian, and when the flux
per plaquette is small compared to the fundamental flux quantum one only needs
to include nearest and next nearest neighbor hoppings. We suggest how to
realize this model using atoms in optical lattices, and describe observable
consequences of the resulting fractional quantum Hall physics.Comment: 4 pages, 3 figures. Published versio
Multiply-connected Bose-Einstein condensed alkali gases: Current-carrying states and their decay
The ability to support metastable current-carrying states in
multiply-connected settings is one of the prime signatures of superfluidity.
Such states are investigated theoretically for the case of trapped Bose
condensed alkali gases, particularly with regard to the rate at which they
decay via thermal fluctuations. The lifetimes of metastable currents can be
either longer or shorter than experimental time-scales. A scheme for the
experimental detection of metastable states is sketched.Comment: 4 pages, including 1 figure (REVTEX
Exact quantum Monte Carlo study of one dimensional trapped fermions with attractive contact interactions
Using exact continuous quantum Monte Carlo techniques, we study the zero and
finite temperature properties of a system of harmonically trapped one
dimensional spin 1/2 fermions with short range interactions. Motivated by
experimental searches for modulated Fulde-Ferrel-Larkin-Ovchinikov states, we
systematically examine the impact of a spin imbalance on the density profiles.
We quantify the accuracy of the Thomas-Fermi approximation, finding that for
sufficiently large particle numbers (N > 100) it quantitatively reproduces most
features of the exact density profile. The Thomas-Fermi approximation fails to
capture small Friedel-like spin and density oscillations and overestimates the
size of the fully paired region in the outer shell of the trap. Based on our
results, we suggest a range of experimentally tunable parameters to maximize
the visibility of the double shell structure of the system and the
Fulde-Ferrel-Larkin-Ovchinikov state in the one dimensional harmonic trap.
Furthermore, we analyze the fingerprints of the attractive contact interactions
in the features of the momentum and pair momentum distributions.Comment: 11 pages, 10 figure
Two-component Bose-Einstein Condensates with Large Number of Vortices
We consider the condensate wavefunction of a rapidly rotating two-component
Bose gas with an equal number of particles in each component. If the
interactions between like and unlike species are very similar (as occurs for
two hyperfine states of Rb or Na) we find that the two components
contain identical rectangular vortex lattices, where the unit cell has an
aspect ratio of , and one lattice is displaced to the center of the
unit cell of the other. Our results are based on an exact evaluation of the
vortex lattice energy in the large angular momentum (or quantum Hall) regime.Comment: 4 pages, 2 figures, RevTe
Fragmentation of Bose-Einstein Condensates
We present the theory of bosonic systems with multiple condensates, unifying
disparate models which are found in the literature, and discuss how
degeneracies, interactions, and symmetries conspire to give rise to this
unusual behavior. We show that as degeneracies multiply, so do the types of
fragmentation, eventually leading to strongly correlated states with no trace
of condensation.Comment: 16 pages, 1 figure, revtex
Climate, wildfire, and erosion ensemble foretells more sediment in western USA watersheds
The area burned annually by wildfires is expected to increase worldwide due to climate change. Burned areas increase soil erosion rates within watersheds, which can increase sedimentation in downstream rivers and reservoirs. However, which watersheds will be impacted by future wildfires is largely unknown. Using an ensemble of climate, fire, and erosion models, we show that postfire sedimentation is projected to increase for nearly nine tenths of watersheds by \u3e10% and for more than one third of watersheds by \u3e100% by the 2041 to 2050 decade in the western USA. The projected increases are statistically significant for more than eight tenths of the watersheds. In the western USA, many human communities rely on water from rivers and reservoirs that originates in watersheds where sedimentation is projected to increase. Increased sedimentation could negatively impact water supply and quality for some communities, in addition to affecting stream channel stability and aquatic ecosystems
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