2,068 research outputs found
Bosons in one-dimensional incommensurate superlattices
We investigate numerically the zero-temperature physics of the
one-dimensional Bose-Hubbard model in an incommensurate cosine potential,
recently realized in experiments with cold bosons in optical superlattices L.
Fallani et al., Phys. Rev. Lett. 98, 130404, (2007)]. An incommensurate cosine
potential has intermediate properties between a truly periodic and a fully
random potential, displaying a characteristic length scale (the quasi-period)
which is shown to set a finite lower bound to the excitation energy of the
system at special incommensurate fillings. This leads to the emergence of
gapped incommensurate band-insulator (IBI) phases along with gapless Bose-glass
(BG) phases for strong quasi-periodic potential, both for hardcore and softcore
bosons. Enriching the spatial features of the potential by the addition of a
second incommensurate component appears to remove the IBI regions, stabilizing
a continuous BG phase over an extended parameter range. Moreover we discuss the
validity of the local-density approximation in presence of a parabolic trap,
clarifying the notion of a local BG phase in a trapped system; we investigate
the behavior of first- and second-order coherence upon increasing the strength
of the quasi-periodic potential; and we discuss the ab-initio derivation of the
Bose-Hubbard Hamiltonian with quasi-periodic potential starting from the
microscopic Hamiltonian of bosons in an incommensurate superlattice.Comment: 22 pages, 28 figure
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.
Localization of a Bose-Einstein condensate vortex in a bichromatic optical lattice
By numerical simulation of the time-dependent Gross-Pitaevskii equation we
show that a weakly interacting or noninteracting Bose-Einstein condensate (BEC)
vortex can be localized in a three-dimensional bichromatic quasi-periodic
optical-lattice (OL) potential generated by the superposition of two
standing-wave polarized laser beams with incommensurate wavelengths. This is a
generalization of the localization of a BEC in a one-dimensional bichromatic OL
as studied in a recent experiment [Roati et al., Nature 453, 895 (2008)]. We
demonstrate the stability of the localized state by considering its time
evolution in the form of a stable breathing oscillation in a slightly altered
potential for a large period of time. {Finally, we consider the localization of
a BEC in a random 1D potential in the form of several identical repulsive
spikes arbitrarily distributed in space
Extremely Low Loss Phonon-Trapping Cryogenic Acoustic Cavities for Future Physical Experiments
Low loss Bulk Acoustic Wave devices are considered from the point of view of
the solid state approach as phonon-confining cavities. We demonstrate effective
design of such acoustic cavities with phonon-trapping techniques exhibiting
extremely high quality factors for trapped longitudinally-polarized phonons of
various wavelengths. Quality factors of observed modes exceed 1 billion, with a
maximum -factor of 8 billion and product of at
liquid helium temperatures. Such high sensitivities allow analysis of intrinsic
material losses in resonant phonon systems. Various mechanisms of phonon losses
are discussed and estimated
Phases of Josephson Junction Ladders
We study a Josephson junction ladder in a magnetic field in the absence of
charging effects via a transfer matrix formalism. The eigenvalues of the
transfer matrix are found numerically, giving a determination of the different
phases of the ladder. The spatial periodicity of the ground state exhibits a
devil's staircase as a function of the magnetic flux filling factor . If the
transverse Josephson coupling is varied a continuous superconducting-normal
transition in the transverse direction is observed, analogous to the breakdown
of the KAM trajectories in dynamical systems.Comment: 12 pages with 3 figures, REVTE
Localization of a Bose-Einstein condensate in a bichromatic optical lattice
By direct numerical simulation of the time-dependent Gross-Pitaevskii
equation we study different aspects of the localization of a non-interacting
ideal Bose-Einstein condensate (BEC) in a one-dimensional bichromatic
quasi-periodic optical-lattice potential. Such a quasi-periodic potential, used
in a recent experiment on the localization of a BEC [Roati et al., Nature 453,
895 (2008)], can be formed by the superposition of two standing-wave polarized
laser beams with different wavelengths. We investigate the effect of the
variation of optical amplitudes and wavelengths on the localization of a
non-interacting BEC. We also simulate the non-linear dynamics when a
harmonically trapped BEC is suddenly released into a quasi-periodic potential,
{as done experimentally in a laser speckle potential [Billy et al., Nature 453,
891 (2008)]$ We finally study the destruction of the localization in an
interacting BEC due to the repulsion generated by a positive scattering length
between the bosonic atoms.Comment: 8 page
Enhanced soliton transport in quasi-periodic lattices with short-range aperiodicity
We study linear transmission and nonlinear soliton transport through
quasi-periodic structures, which profiles are described by multiple modulation
frequencies. We show that resonant scattering at mixed-frequency resonances
limits transmission efficiency of localized wave packets, leading to radiation
and possible trapping of solitons. We obtain an explicit analytical expression
for optimal quasi-periodic lattice profiles, where additional aperiodic
modulations suppress mixed-frequency resonances, resulting in dramatic
enhancement of soliton mobility. Our results can be applied to the design of
photonic waveguide structures, and arrays of magnetic micro-traps for atomic
Bose-Einstein condensates.Comment: 4 pages, 4 figure
Asymptotic entanglement in 1D quantum walks with a time-dependent coined
Discrete-time quantum walk evolve by a unitary operator which involves two
operators a conditional shift in position space and a coin operator. This
operator entangles the coin and position degrees of freedom of the walker. In
this paper, we investigate the asymptotic behavior of the coin position
entanglement (CPE) for an inhomogeneous quantum walk which determined by two
orthogonal matrices in one-dimensional lattice. Free parameters of coin
operator together provide many conditions under which a measurement perform on
the coin state yield the value of entanglement on the resulting position
quantum state. We study the problem analytically for all values that two free
parameters of coin operator can take and the conditions under which
entanglement becomes maximal are sought.Comment: 23 pages, 4 figures, accepted for publication in IJMPB. arXiv admin
note: text overlap with arXiv:1001.5326 by other author
Magnetization of two coupled rings
We investigate the persistent currents and magnetization of a mesoscopic
system consisting of two clean metallic rings sharing a single contact point in
a magnetic field. Many novel features with respect to the single-ring geometry
are underlined, including the explicit dependence of wavefunctions on the
Aharonov-Bohm fluxes, the complex pattern of twofold and threefold
degeneracies, the key role of length and flux commensurability, and in the case
of commensurate ring lengths the occurrence of idle levels which do not carry
any current. Spin-orbit interactions, induced by the electric fields of charged
wires threading the rings, give rise to a peculiar version of the
Aharonov-Casher effect where, unlike for a single ring, spin is not conserved.
Remarkably enough, this can only be realized when the Aharonov-Bohm fluxes in
both rings are neither integer nor half-integer multiples of the flux quantum.Comment: 27 pages, 10 figures, 4 tables. A few references added and other
minor change
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