2,740 research outputs found
Damping and decoherence of Fock states in a nanomechanical resonator due to two level systems
We numerically investigate the decay of initial quantum Fock states and their
superpositions for a mechanical resonator mode coupled to an environment
comprising interacting, damped tunneling two level system (TLS) defects. The
cases of one, three, and six near resonant, interacting TLS's are considered in
turn and it is found that the resonator displays Ohmic bath like decay behavior
with as few as three TLS's.Comment: 28 pages, 24 figures; submitted to Physical Review
Achievable Qubit Rates for Quantum Information Wires
Suppose Alice and Bob have access to two separated regions, respectively, of
a system of electrons moving in the presence of a regular one-dimensional
lattice of binding atoms. We consider the problem of communicating as much
quantum information, as measured by the qubit rate, through this quantum
information wire as possible. We describe a protocol whereby Alice and Bob can
achieve a qubit rate for these systems which is proportional to N^(-1/3) qubits
per unit time, where N is the number of lattice sites. Our protocol also
functions equally in the presence of interactions modelled via the t-J and
Hubbard models
Fast field-cycling NMR of cartilage : a way toward molecular imaging
Peer reviewedPublisher PD
Superfluid Fermi gas in a 1D optical lattice
We calculate the superfluid transition temperature for a two-component 3D
Fermi gas in a 1D tight optical lattice and discuss a dimensional crossover
from the 3D to quasi-2D regime. For the geometry of finite size discs in the 1D
lattice, we find that even for a large number of atoms per disc, the critical
effective tunneling rate for a quantum transition to the Mott insulator state
can be large compared to the loss rate caused by three-body recombination. This
allows the observation of the Mott transition, in contrast to the case of
Bose-condensed gases in the same geometry.Comment: 4 pages, 1 figur
From bcc to fcc: interplay between oscillating long-range and repulsive short-range forces
This paper supplements and partly extends an earlier publication, Phys. Rev.
Lett. 95, 265501 (2005). In -dimensional continuous space we describe the
infinite volume ground state configurations (GSCs) of pair interactions \vfi
and \vfi+\psi, where \vfi is the inverse Fourier transform of a nonnegative
function vanishing outside the sphere of radius , and is any
nonnegative finite-range interaction of range , where
. In three dimensions the decay of \vfi can be as slow
as , and an interaction of asymptotic form
is among the examples. At a dimension-dependent
density the ground state of \vfi is a unique Bravais lattice, and
for higher densities it is continuously degenerate: any union of Bravais
lattices whose reciprocal lattice vectors are not shorter than is a GSC.
Adding decreases the ground state degeneracy which, nonetheless, remains
continuous in the open interval , where is the
close-packing density of hard balls of diameter . The ground state is
unique at both ends of the interval. In three dimensions this unique GSC is the
bcc lattice at and the fcc lattice at .Comment: Published versio
Coherent phonon scattering effects on thermal transport in thin semiconductor nanowires
The thermal conductance by phonons of a quasi-one-dimensional solid with
isotope or defect scattering is studied using the Landauer formalism for
thermal transport. The conductance shows a crossover from localized to Ohmic
behavior, just as for electrons, but the nature of this crossover is modified
by delocalization of phonons at low frequency. A scalable numerical
transfer-matrix technique is developed and applied to model
quasi-one-dimensional systems in order to confirm simple analytic predictions.
We argue that existing thermal conductivity data on semiconductor nanowires,
showing an unexpected linear dependence, can be understood through a model that
combines incoherent surface scattering for short-wavelength phonons with nearly
ballistic long-wavelength phonons. It is also found that even when strong
phonon localization effects would be observed if defects are distributed
throughout the wire, localization effects are much weaker when defects are
localized at the boundary, as in current experiments.Comment: 13 page
Inherent Structures for Soft Long-Range Interactions in Two-Dimensional Many-Particle Systems
We generate inherent structures, local potential-energy minima, of the
"-space overlap potential" in two-dimensional many-particle systems using a
cooling and quenching simulation technique. The ground states associated with
the -space overlap potential are stealthy ({\it i.e.,} completely suppress
single scattering of radiation for a range of wavelengths) and hyperuniform
({\it i.e.,} infinite wavelength density fluctuations vanish). However, we show
via quantitative metrics that the inherent structures exhibit a range of
stealthiness and hyperuniformity depending on the fraction of degrees of
freedom that are constrained. Inherent structures in two dimensions typically
contain five-particle rings, wavy grain boundaries, and vacancy-interstitial
defects. The structural and thermodynamic properties of inherent structures are
relatively insensitive to the temperature from which they are sampled,
signifying that the energy landscape is relatively flat and devoid of deep
wells. Using the nudged-elastic-band algorithm, we construct paths from
ground-state configurations to inherent structures and identify the transition
points between them. In addition, we use point patterns generated from a random
sequential addition (RSA) of hard disks, which are nearly stealthy, and examine
the particle rearrangements necessary to make the configurations absolutely
stealthy. We introduce a configurational proximity metric to show that only
small local, but collective, particle rearrangements are needed to drive
initial RSA configurations to stealthy disordered ground states. These results
lead to a more complete understanding of the unusual behaviors exhibited by the
family of "collective-coordinate" potentials to which the -space overlap
potential belongs.Comment: 36 pages, 16 figure
Neutron specific heat in the crust of neutron stars from the nuclear band theory
The inner crust of neutron stars, formed of a crystal lattice of uclear
clusters immersed in a sea of unbound neutrons, may be the nique example of
periodic nuclear systems. We have calculated the neutron specific heat in the
shallow part of the crust using the band theory of solids with Skyrme
nucleon-nucleon interactions. We have also tested the validity of various
approximations. We have found that the neutron specific heat is well described
by that of a Fermi gas, while the motion of the unbound neutrons is strongly
affected by the nuclear lattice. These apparently contradictory results are
explained by the particular properties of the neutron Fermi surface
Bright gap solitons of atoms with repulsive interaction
We report on the first experimental observation of bright matter-wave
solitons for 87Rb atoms with repulsive atom-atom interaction. This counter
intuitive situation arises inside a weak periodic potential, where anomalous
dispersion can be realized at the Brillouin zone boundary. If the coherent
atomic wavepacket is prepared at the corresponding band edge a bright soliton
is formed inside the gap. The strength of our system is the precise control of
preparation and real time manipulation, allowing the systematic investigation
of gap solitons.Comment: 4 pages, 4 figure
Rare-gas solids under pressure: A path-integral Monte Carlo simulation
Rare-gas solids (Ne, Ar, Kr, and Xe) under hydrostatic pressure up to 30 kbar
have been studied by path-integral Monte Carlo simulations in the
isothermal-isobaric ensemble. Results of these simulations have been compared
with available experimental data and with those obtained from a quasiharmonic
approximation (QHA). This comparison allows us to quantify the overall
anharmonicity of the lattice vibrations and its influence on several structural
and thermodynamic properties of rare-gas solids. The vibrational energy
increases with pressure, but this increase is slower than that of the elastic
energy, which dominates at high pressures. In the PIMC simulations, the
vibrational kinetic energy is found to be larger than the corresponding
potential energy, and the relative difference between both energies decreases
as the applied pressure is raised. The accuracy of the QHA increases for rising
pressure.Comment: 9 pages, 6 figure
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