70 research outputs found
Bose-enhanced chemistry: Amplification of selectivity in the dissociation of molecular Bose-Einstein condensates
We study the photodissociation chemistry of a quantum degenerate gas of
bosonic triatomic molecules, assuming two open rearrangement channels
( or ). The equations of motion are equivalent to those of a
parametric multimode laser, resulting in an exponential buildup of macroscopic
mode populations. By exponentially amplifying a small differential in the
single-particle rate-coefficients, Bose stimulation leads to a nearly complete
selectivity of the collective -body process, indicating a novel type of
ultra-selective quantum degenerate chemistry.Comment: 5 pages, 3 figure
Three-body recombination in Bose gases with large scattering length
An effective field theory for the three-body system with large scattering
length is applied to three-body recombination to a weakly-bound s-wave state in
a Bose gas. Our model independent analysis demonstrates that the three-body
recombination constant alpha is not universal, but can take any value between
zero and 67.9 \hbar a^4/m, where a is the scattering length. Other low-energy
three-body observables can be predicted in terms of a and alpha. Near a
Feshbach resonance, alpha should oscillate between those limits as the magnetic
field B approaches the point where a -> infinity. In any interval of B over
which a increases by a factor of 22.7, alpha should have a zero.Comment: 8 pages, RevTex, 3 postscript figures, uses epsf.sty, rotate.sty,
references added, discussion improve
Resonance Superfluidity: Renormalization of Resonance Scattering Theory
We derive a theory of superfluidity for a dilute Fermi gas that is valid when
scattering resonances are present. The treatment of a resonance in many-body
atomic physics requires a novel mean-field approach starting from an
unconventional microscopic Hamiltonian. The mean-field equations incorporate
the microscopic scattering physics, and the solutions to these equations
reproduce the energy-dependent scattering properties. This theory describes the
high- behavior of the system, and predicts a value of which is a
significant fraction of the Fermi temperature. It is shown that this novel
mean-field approach does not break down for typical experimental circumstances,
even at detunings close to resonance. As an example of the application of our
theory we investigate the feasibility for achieving superfluidity in an
ultracold gas of fermionic Li.Comment: 15 pages, 10 figure
Elastic and inelastic collisions of 6Li in magnetic and optical traps
We use a full coupled channels method to calculate collisional properties of
magnetically or optically trapped ultracold 6Li. The magnetic field dependence
of the s-wave scattering lengths of several mixtures of hyperfine states are
determined, as are the decay rates due to exchange collisions. In one case, we
find Feshbach resonances at B=0.08 T and B=1.98 T. We show that the exact
coupled channels calculation is well approximated over the entire range of
magnetic fields by a simple analytical calculation.Comment: 4 pages revtex including 4 figures, submitted to PR
Feshbach-Stimulated Photoproduction of a Stable Molecular Condensate
Photoassociation and the Feshbach resonance are, in principle, feasible means
for creating a molecular Bose-Einstein condensate from an
already-quantum-degenerate gas of atoms; however, mean-field shifts and
irreversible decay place practical constraints on the efficient delivery of
stable molecules using either mechanism alone. We therefore propose
Feshbach-stimulated Raman photoproduction, i.e., a combination of magnetic and
optical methods, as a viable means to collectively convert degenerate atoms
into a stable molecular condensate with near-unit efficiency.Comment: 5 pages, 3 figures, 1 table; v3 includes few-level diagram of scheme,
and added discussion; transferred to PR
High-precision calculations of dispersion coefficients, static dipole polarizabilities, and atom-wall interaction constants for alkali-metal atoms
The van der Waals coefficients for the alkali-metal atoms from Na to Fr
interacting in their ground states, are calculated using relativistic ab initio
methods. The accuracy of the calculations is estimated by also evaluating
atomic static electric dipole polarizabilities and coefficients for the
interaction of the atoms with a perfectly conducting wall. The results are in
excellent agreement with the latest data from ultra-cold collisions and from
studies of magnetic field induced Feshbach resonances in Na and Rb. For Cs we
provide critically needed data for ultra-cold collision studies
Stimulated Raman adiabatic passage from an atomic to a molecular Bose-Einstein condensate
The process of stimulated Raman adiabatic passage (STIRAP) provides a
possible route for the generation of a coherent molecular Bose-Einstein
condensate (BEC) from an atomic BEC. We analyze this process in a
three-dimensional mean-field theory, including atom-atom interactions and
non-resonant intermediate levels. We find that the process is feasible, but at
larger Rabi frequencies than anticipated from a crude single-mode lossless
analysis, due to two-photon dephasing caused by the atomic interactions. We
then identify optimal strategies in STIRAP allowing one to maintain high
conversion efficiencies with smaller Rabi frequencies and under experimentally
less demanding conditions.Comment: Final published versio
Stationary solutions of the one-dimensional nonlinear Schroedinger equation: II. Case of attractive nonlinearity
All stationary solutions to the one-dimensional nonlinear Schroedinger
equation under box or periodic boundary conditions are presented in analytic
form for the case of attractive nonlinearity. A companion paper has treated the
repulsive case. Our solutions take the form of bounded, quantized, stationary
trains of bright solitons. Among them are two uniquely nonlinear classes of
nodeless solutions, whose properties and physical meaning are discussed in
detail. The full set of symmetry-breaking stationary states are described by
the character tables from the theory of point groups. We make
experimental predictions for the Bose-Einstein condensate and show that, though
these are the analog of some of the simplest problems in linear quantum
mechanics, nonlinearity introduces new and surprising phenomena.Comment: 11 pages, 9 figures -- revised versio
Microscopic Dynamics in a Strongly Interacting Bose-Einstein Condensate
An initially stable 85Rb Bose-Einstein condensate (BEC) was subjected to a
carefully controlled magnetic field pulse in the vicinity of a Feshbach
resonance. This pulse probed the strongly interacting regime for the
condensate, with calculated values for the diluteness parameter (na^3) ranging
from 0.01 to 0.5. The field pulse was observed to cause loss of atoms from the
condensate on remarkably short time scales (>=10 microsec). The dependence of
this loss on magnetic field pulse shape and amplitude was measured. For
triangular pulses shorter than 1 ms, decreasing the pulse length actually
increased the loss, until extremely short time scales (a few tens of
microseconds) were reached. Such time scales and dependencies are very
different from those expected in traditional condensate inelastic loss
processes, suggesting the presence of new microscopic BEC physics.Comment: 4 pages in latex2E, 4 eps figures; revised Fig.1, revised
scatt.lengths, added discussion, new refs., resubmitted to PR
- …