3,060 research outputs found
Exploring the grand-canonical phase diagram of interacting bosons in optical lattices by trap squeezing
In this paper we theoretically discuss how quantum simulators based on
trapped cold bosons in optical lattices can explore the grand-canonical phase
diagram of homogeneous lattice boson models, via control of the trapping
potential independently of all other experimental parameters (trap squeezing).
Based on quantum Monte Carlo, we establish the general scaling relation linking
the global chemical potential to the Hamiltonian parameters of the Bose-Hubbard
model in a parabolic trap, describing cold bosons in optical lattices; we find
that this scaling relation is well captured by a modified Thomas-Fermi scaling
behavior - corrected for quantum fluctuations - in the case of high enough
density and/or weak enough interactions, and by a mean-field Gutzwiller Ansatz
over a much larger parameter range. The above scaling relation allows to
control experimentally the chemical potential, independently of all other
Hamiltonian parameters, via trap squeezing; given that the global chemical
potential coincides with the local chemical potential in the trap center,
measurements of the central density as a function of the chemical potential
gives access to the information on the bulk compressibility of the Bose-Hubbard
model. Supplemented with time-of-flight measurements of the coherence
properties, the measurement of compressibility enables one to discern among the
various possible phases realized by bosons in an optical lattice with or
without external (periodic or random) potentials -- e.g. superfluid, Mott
insulator, band insulator, and Bose glass. We theoretically demonstrate the
trap-squeezing investigation of the above phases in the case of bosons in a
one-dimensional optical lattice, and in a one-dimensional incommensurate
superlattice.Comment: 27 pages, 26 figures. v2: added references and further discussion of
the local-density approximation
Order in extremal trajectories
Given a chaotic dynamical system and a time interval in which some quantity
takes an unusually large average value, what can we say of the trajectory that
yields this deviation? As an example, we study the trajectories of the
archetypical chaotic system, the baker's map. We show that, out of all
irregular trajectories, a large-deviation requirement selects (isolated) orbits
that are periodic or quasiperiodic. We discuss what the relevance of this
calculation may be for dynamical systems and for glasses
Mode solutions for a Klein-Gordon field in anti-de Sitter spacetime with dynamical boundary conditions of Wentzell type
We study a real, massive Klein-Gordon field in the Poincar\'e fundamental
domain of the -dimensional anti-de Sitter (AdS) spacetime, subject to a
particular choice of dynamical boundary conditions of generalized Wentzell
type, whereby the boundary data solves a non-homogeneous, boundary Klein-Gordon
equation, with the source term fixed by the normal derivative of the scalar
field at the boundary. This naturally defines a field in the conformal boundary
of the Poincar\'e fundamental domain of AdS. We completely solve the equations
for the bulk and boundary fields and investigate the existence of bound state
solutions, motivated by the analogous problem with Robin boundary conditions,
which are recovered as a limiting case. Finally, we argue that both Robin and
generalized Wentzell boundary conditions are distinguished in the sense that
they are invariant under the action of the isometry group of the AdS conformal
boundary, a condition which ensures in addition that the total flux of energy
across the boundary vanishes.Comment: 12 pages, 1 figure. In V3: refs. added, introduction and conclusions
expande
The Exact Ground State of the Frenkel-Kontorova Model with Repeated Parabolic Potential: I. Basic Results
The problem of finding the exact energies and configurations for the
Frenkel-Kontorova model consisting of particles in one dimension connected to
their nearest-neighbors by springs and placed in a periodic potential
consisting of segments from parabolas of identical (positive) curvature but
arbitrary height and spacing, is reduced to that of minimizing a certain convex
function defined on a finite simplex.Comment: 12 RevTeX pages, using AMS-Fonts (amssym.tex,amssym.def), 6
Postscript figures, accepted by Phys. Rev.
Controlling Mixing Inside a Droplet by Time Dependent Rigid-body Rotation
The use of microscopic discrete fluid volumes (i.e., droplets) as
microreactors for digital microfluidic applications often requires mixing
enhancement and control within droplets. In this work, we consider a
translating spherical liquid droplet to which we impose a time periodic
rigid-body rotation which we model using the superposition of a Hill vortex and
an unsteady rigid body rotation. This perturbation in the form of a rotation
not only creates a three-dimensional chaotic mixing region, which operates
through the stretching and folding of material lines, but also offers the
possibility of controlling both the size and the location of the mixing. Such a
control is achieved by judiciously adjusting the three parameters that
characterize the rotation, i.e., the rotation amplitude, frequency and
orientation of the rotation. As the size of the mixing region is increased,
complete mixing within the drop is obtained.Comment: 6 pages, 6 figure
Retrieving time-dependent Green's functions in optics with low-coherence interferometry
We report on the passive measurement of time-dependent Green's functions in
the optical frequency domain with low-coherence interferometry. Inspired by
previous studies in acoustics and seismology, we show how the correlations of a
broadband and incoherent wave-field can directly yield the Green's functions
between scatterers of a complex medium. Both the ballistic and multiple
scattering components of the Green's function are retrieved. This approach
opens important perspectives for optical imaging and characterization in
complex scattering media.Comment: 5 pages, 4 figure
Finite-size effects in Anderson localization of one-dimensional Bose-Einstein condensates
We investigate the disorder-induced localization transition in Bose-Einstein
condensates for the Anderson and Aubry-Andre models in the non-interacting
limit using exact diagonalization. We show that, in addition to the standard
superfluid fraction, other tools such as the entanglement and fidelity can
provide clear signatures of the transition. Interestingly, the fidelity
exhibits good sensitivity even for small lattices. Effects of the system size
on these quantities are analyzed in detail, including the determination of a
finite-size-scaling law for the critical disorder strength in the case of the
Anderson model.Comment: 15 pages, 7 figure
On inward motion of the magnetopause preceding a substorm
Magnetopause inward motion preceding magnetic storms observed by means of OGO-E magnetomete
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