700 research outputs found
Analysis and Optimization of Mixed-Criticality Applications on Partitioned Distributed Architectures
Zeros of Rydberg-Rydberg Foster Interactions
Rydberg states of atoms are of great current interest for quantum
manipulation of mesoscopic samples of atoms. Long-range Rydberg-Rydberg
interactions can inhibit multiple excitations of atoms under the appropriate
conditions. These interactions are strongest when resonant collisional
processes give rise to long-range C_3/R^3 interactions. We show in this paper
that even under resonant conditions C_3 often vanishes so that care is required
to realize full dipole blockade in micron-sized atom samples.Comment: 10 pages, 4 figures, submitted to J. Phys.
Probing dipolar effects with condensate shape oscillation
We discuss the low energy shape oscillations of a magnetic trapped atomic
condensate including the spin dipole interaction. When the nominal isotropic
s-wave interaction strength becomes tunable through a Feshbach resonance (e.g.
as for Rb atoms), anisotropic dipolar effects are shown to be detectable
under current experimental conditions [E. A. Donley {\it et al.}, Nature {\bf
412}, 295 (2001)].Comment: revised version, submitte
Calculation of the interspecies s-wave scattering length in an ultracold Na-Rb vapor
We report the calculation of the interspecies scattering length for the
sodium-rubidium (Na-Rb) system. We present improved hybrid potentials for the
singlet and triplet ground states of the NaRb
molecule, and calculate the singlet and triplet scattering lengths and
for the isotopomers NaRb and NaRb. Using
these values, we assess the prospects for producing a stable two-species
Bose-Einstein condensate in the Na-Rb system.Comment: v2: report correct units in Table captions, fix error in conclusions
for NaRb TBEC. Otherwise, more concise presentation, typos
fixed. 6 pages, 1 figur
Low energy atomic collision with dipole interactions
We apply quantum defect theory to study low energy ground state atomic
collisions including aligned dipole interactions such as those induced by an
electric field. Our results show that coupled even () relative orbital
angular momentum partial wave channels exhibit shape resonance structures while
odd () channels do not. We analyze and interpret these resonances within the
framework of multichannel quantum defect theory (MQDT).Comment: 27 pages, 17 figures, an inadvertent typo correcte
Strong dipolar effects in a quantum ferrofluid
We report on the realization of a Chromium Bose-Einstein condensate (BEC)
with strong dipolar interaction. By using a Feshbach resonance, we reduce the
usual isotropic contact interaction, such that the anisotropic magnetic
dipole-dipole interaction between 52Cr atoms becomes comparable in strength.
This induces a change of the aspect ratio of the cloud, and, for strong dipolar
interaction, the inversion of ellipticity during expansion - the usual "smoking
gun" evidence for BEC - can even be suppressed. These effects are accounted for
by taking into account the dipolar interaction in the superfluid hydrodynamic
equations governing the dynamics of the gas, in the same way as classical
ferrofluids can be described by including dipolar terms in the classical
hydrodynamic equations. Our results are a first step in the exploration of the
unique properties of quantum ferrofluids.Comment: Final, published versio
Spin instabilities and quantum phase transitions in integral and fractional quantum Hall states
The inter-Landau-level spin excitations of quantum Hall states at filling
factors nu=2 and 4/3 are investigated by exact numerical diagonalization for
the situation in which the cyclotron (hbar*omega_c) and Zeeman (E_Z) splittings
are comparable. The relevant quasiparticles and their interactions are studied,
including stable spin wave and skyrmion bound states. For nu=2, a spin
instability at a finite value of epsilon=hbar*omega_c-E_Z leads to an abrupt
paramagnetic to ferromagnetic transition, in agreement with the mean-field
approximation. However, for nu=4/3 a new and unexpected quantum phase
transition is found which involves a gradual change from paramagnetic to
ferromagnetic occupancy of the partially filled Landau level as epsilon is
decreased.Comment: 4 pages, 5 figures, submitted to Phys.Rev.Let
Pair distribution function in a two-dimensional electron gas
We calculate the pair distribution function, , in a two-dimensional
electron gas and derive a simple analytical expression for its value at the
origin as a function of . Our approach is based on solving the
Schr\"{o}dinger equation for the two-electron wave function in an appropriate
effective potential, leading to results that are in good agreement with Quantum
Monte Carlo data and with the most recent numerical calculations of . [C.
Bulutay and B. Tanatar, Phys. Rev. B {\bf 65}, 195116 (2002)] We also show that
the spin-up spin-down correlation function at the origin, , is mainly independent of the degree of spin polarization of
the electronic system.Comment: 5 figures, pair distribution dependence with distance is calculate
Exploring a quantum degenerate gas of fermionic atoms
We predict novel phenomena in the behavior of an ultra- cold, trapped gas of
fermionic atoms. We find that quantum statistics radically changes the
collisional properties, spatial profile, and off-resonant light scattering
properties of the atomic fermion system, and we suggest how these effects can
be observed.Comment: 5 pages, 3 figure
The variable phase method used to calculate and correct scattering lengths
It is shown that the scattering length can be obtained by solving a Riccati
equation derived from variable phase theory. Two methods of solving it are
presented. The equation is used to predict how long-range interactions
influence the scattering length, and upper and lower bounds on the scattering
length are determined. The predictions are compared with others and it is shown
how they may be obtained from secular perturbation theory.Comment: 7 pages including 3 figure
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