1,302 research outputs found
Discerning Incompressible and Compressible Phases of Cold Atoms in Optical Lattices
Experiments with cold atoms trapped in optical lattices offer the potential
to realize a variety of novel phases but suffer from severe spatial
inhomogeneity that can obscure signatures of new phases of matter and phase
boundaries. We use a high temperature series expansion to show that
compressibility in the core of a trapped Fermi-Hubbard system is related to
measurements of changes in double occupancy. This core compressibility filters
out edge effects, offering a direct probe of compressibility independent of
inhomogeneity. A comparison with experiments is made
Thermalization of strongly interacting bosons after spontaneous emissions in optical lattices
We study the out-of-equilibrium dynamics of bosonic atoms in a 1D optical
lattice, after the ground-state is excited by a single spontaneous emission
event, i.e. after an absorption and re-emission of a lattice photon. This is an
important fundamental source of decoherence for current experiments, and
understanding the resulting dynamics and changes in the many-body state is
important for controlling heating in quantum simulators. Previously it was
found that in the superfluid regime, simple observables relax to values that
can be described by a thermal distribution on experimental time-scales, and
that this breaks down for strong interactions (in the Mott insulator regime).
Here we expand on this result, investigating the relaxation of the momentum
distribution as a function of time, and discussing the relationship to
eigenstate thermalization. For the strongly interacting limit, we provide an
analytical analysis for the behavior of the system, based on an effective
low-energy Hamiltonian in which the dynamics can be understood based on
correlated doublon-holon pairs.Comment: 8 pages, 5 figure
The use of data-mining for the automatic formation of tactics
This paper discusses the usse of data-mining for the automatic formation of tactics. It was presented at the Workshop on Computer-Supported Mathematical Theory Development held at IJCAR in 2004. The aim of this project is to evaluate the applicability of data-mining techniques to the automatic formation of tactics from large corpuses of proofs. We data-mine information from large proof corpuses to find commonly occurring patterns. These patterns are then evolved into tactics using genetic programming techniques
Ultracold atoms in one-dimensional optical lattices approaching the Tonks-Girardeau regime
Recent experiments on ultracold atomic alkali gases in a one-dimensional
optical lattice have demonstrated the transition from a gas of soft-core bosons
to a Tonks-Girardeau gas in the hard-core limit, where one-dimensional bosons
behave like fermions in many respects. We have studied the underlying many-body
physics through numerical simulations which accommodate both the soft-core and
hard-core limits in one single framework. We find that the Tonks-Girardeau gas
is reached only at the strongest optical lattice potentials. Results for
slightly higher densities, where the gas develops a Mott-like phase already at
weaker optical lattice potentials, show that these Mott-like short range
correlations do not enhance the convergence to the hard-core limit.Comment: 4 pages, 3 figures, replaced with published versio
Evidence for hard and soft substructures in thermoelectric SnSe
SnSe is a topical thermoelectric material with a low thermal conductivity
which is linked to its unique crystal structure. We use low-temperature heat
capacity measurements to demonstrate the presence of two characteristic
vibrational energy scales in SnSe with Debye temperatures thetaD1 = 345(9) K
and thetaD2 = 154(2) K. These hard and soft substructures are quantitatively
linked to the strong and weak Sn-Se bonds in the crystal structure. The heat
capacity model predicts the temperature evolution of the unit cell volume,
confirming that this two-substructure model captures the basic thermal
properties. Comparison with phonon calculations reveals that the soft
substructure is associated with the low energy phonon modes that are
responsible for the thermal transport. This suggests that searching for
materials containing highly divergent bond distances should be a fruitful route
for discovering low thermal conductivity materials.Comment: Accepted by Applied Physics Letter
Maximum occupation number for composite boson states
One of the major differences between fermions and bosons is that fermionic
states have a maximum occupation number of one, whereas the occupation number
for bosonic states is in principle unlimited. For bosons that are made up of
fermions, one could ask the question to what extent the Pauli principle for the
constituent fermions would limit the boson occupation number. Intuitively one
can expect the maximum occupation number to be proportional to the available
volume for the bosons divided by the volume occupied by the fermions inside one
boson, though a rigorous derivation of this result has not been given before.
In this letter we show how the maximum occupation number can be calculated from
the ground-state energy of a fermionic generalized pairing problem. A very
accurate analytical estimate of this eigenvalue is derived. From that a general
expression is obtained for the maximum occupation number of a composite boson
state, based solely on the intrinsic fermionic structure of the bosons. The
consequences for Bose-Einstein condensates of excitons in semiconductors and
ultra cold trapped atoms are discussed.Comment: 4 pages, Revte
Regularization of Diagrammatic Series with Zero Convergence Radius
The divergence of perturbative expansions for the vast majority of
macroscopic systems, which follows from Dyson's collapse argument, prevents
Feynman's diagrammatic technique from being directly used for controllable
studies of strongly interacting systems. We show how the problem of divergence
can be solved by replacing the original model with a convergent sequence of
successive approximations which have a convergent perturbative series. As a
prototypical model, we consider the zero-dimensional
theory.Comment: 4 pages, 3 figure
Dynamical mean field solution of the Bose-Hubbard model
We present the effective action and self-consistency equations for the
bosonic dynamical mean field (B-DMFT) approximation to the bosonic Hubbard
model and show that it provides remarkably accurate phase diagrams and
correlation functions. To solve the bosonic dynamical mean field equations we
use a continuous-time Monte Carlo method for bosonic impurity models based on a
diagrammatic expansion in the hybridization and condensate coupling. This
method is readily generalized to bosonic mixtures, spinful bosons, and
Bose-Fermi mixtures.Comment: 10 pages, 3 figures. includes supplementary materia
Supersolid phase with cold polar molecules on a triangular lattice
We study a system of heteronuclear molecules on a triangular lattice and
analyze the potential of this system for the experimental realization of a
supersolid phase. The ground state phase diagram contains superfluid, solid and
supersolid phases. At finite temperatures and strong interactions there is an
additional emulsion region, in contrast to similar models with short-range
interactions. We derive the maximal critical temperature and the
corresponding entropy for supersolidity and find feasible
experimental conditions for its realization.Comment: 4 pages, 4 figure
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