17,192 research outputs found
Interaction dependent temperature effects in Bose-Fermi mixtures in optical lattices
We present a quantitative finite temperature analysis of a recent experiment
with Bose-Fermi mixtures in optical lattices, in which the dependence of the
coherence of bosons on the inter-species interaction was analyzed. Our theory
reproduces the characteristics of this dependence and suggests that intrinsic
temperature effects play an important role in these systems. Namely, under the
assumption that the ramping up of the optical lattice is an isentropic process,
adiabatic temperature changes of the mixture occur that depend on the
interaction between bosons and fermions. Matching the entropy of two
regimes---no lattice on the one hand and deep lattices on the other---allows us
to compute the temperature in the lattice and the visibility of the
quasi-momentum distribution of the bosonic atoms, which we compare to the
experiment. We briefly comment on the remaining discrepancy between theory and
experiment, speculating that it may in part be attributed to the dependence of
the Bose-Fermi scattering length on the confinement of the atoms.Comment: 6 pages, 3 figure
Thermalization under randomized local Hamiltonians
Recently, there have been significant new insights concerning conditions
under which closed systems equilibrate locally. The question if subsystems
thermalize---if the equilibrium state is independent of the initial state---is
however much harder to answer in general. Here, we consider a setting in which
thermalization can be addressed: A quantum quench under a Hamiltonian whose
spectrum is fixed and basis is drawn from the Haar measure. If the Fourier
transform of the spectral density is small, almost all bases lead to local
equilibration to the thermal state with infinite temperature. This allows us to
show that, under almost all Hamiltonians that are unitarily equivalent to a
local Hamiltonian, it takes an algebraically small time for subsystems to
thermalize.Comment: published versio
A quantum central limit theorem for non-equilibrium systems: Exact local relaxation of correlated states
We prove that quantum many-body systems on a one-dimensional lattice locally
relax to Gaussian states under non-equilibrium dynamics generated by a bosonic
quadratic Hamiltonian. This is true for a large class of initial states - pure
or mixed - which have to satisfy merely weak conditions concerning the decay of
correlations. The considered setting is a proven instance of a situation where
dynamically evolving closed quantum systems locally appear as if they had truly
relaxed, to maximum entropy states for fixed second moments. This furthers the
understanding of relaxation in suddenly quenched quantum many-body systems. The
proof features a non-commutative central limit theorem for non-i.i.d. random
variables, showing convergence to Gaussian characteristic functions, giving
rise to trace-norm closeness. We briefly relate our findings to ideas of
typicality and concentration of measure.Comment: 27 pages, final versio
Quantifying coherence
We introduce a rigorous framework for the quantification of coherence and identify intuitive and easily computable measures of coherence. We achieve this by adopting the viewpoint of coherence as a physical resource. By determining defining conditions for measures of coherence we identify classes of functionals that satisfy these conditions and other, at first glance natural quantities, that do not qualify as coherence measures. We conclude with an outline of the questions that remain to be answered to complete the theory of coherence as a resource
Modeling material failure with a vectorized routine
The computational aspects of modelling material failure in structural wood members are presented with particular reference to vector processing aspects. Wood members are considered to be highly orthotropic, inhomogeneous, and discontinuous due to the complex microstructure of wood material and the presence of natural growth characteristics such as knots, cracks and cross grain in wood members. The simulation of strength behavior of wood members is accomplished through the use of a special purpose finite element/fracture mechanics routine, program STARW (Strength Analysis Routine for Wood). Program STARW employs quadratic finite elements combined with singular crack tip elements in a finite element mesh. Vector processing techniques are employed in mesh generation, stiffness matrix formation, simultaneous equation solution, and material failure calculations. The paper addresses these techniques along with the time and effort requirements needed to convert existing finite element code to a vectorized version. Comparisons in execution time between vectorized and nonvectorized routines are provided
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