154 research outputs found
Strongly enhanced inelastic collisions in a Bose-Einstein condensate near Feshbach resonances
The properties of Bose-Einstein condensed gases can be strongly altered by
tuning the external magnetic field near a Feshbach resonance. Feshbach
resonances affect elastic collisions and lead to the observed modification of
the scattering length. However, as we report here, this is accompanied by a
strong increase in the rate of inelastic collisions. The observed three-body
loss rate in a sodium Bose-Einstein condensation increased when the scattering
length was tuned to both larger or smaller values than the off-resonant value.
This observation and the maximum measured increase of the loss rate by several
orders of magnitude are not accounted for by theoretical treatments. The strong
losses impose severe limitations for using Feshbach resonances to tune the
properties of Bose-Einstein condensates. A new Feshbach resonance in sodium at
1195 G was observed.Comment: 4 pages, 3 figure
Three-body recombination of ultra-cold atoms to a weakly bound level
We discuss three-body recombination of ultra-cold atoms to a weakly bound
level. In this case, characterized by large and positive scattering length
for pair interaction, we find a repulsive effective potential for three-body
collisions, which strongly reduces the recombination probability and makes
simple Jastrow-like approaches absolutely inadequate. In the zero temperature
limit we obtain a universal relation, independent of the detailed shape of the
interaction potential, for the (event) rate constant of three-body
recombination: , where is the atom mass.Comment: 10 pages, 3 Postscript figure
Quantum Computing with Atomic Josephson Junction Arrays
We present a quantum computing scheme with atomic Josephson junction arrays.
The system consists of a small number of atoms with three internal states and
trapped in a far-off resonant optical lattice. Raman lasers provide the
"Josephson" tunneling, and the collision interaction between atoms represent
the "capacitive" couplings between the modes. The qubit states are collective
states of the atoms with opposite persistent currents. This system is closely
analogous to the superconducting flux qubit. Single qubit quantum logic gates
are performed by modulating the Raman couplings, while two-qubit gates result
from a tunnel coupling between neighboring wells. Readout is achieved by tuning
the Raman coupling adiabatically between the Josephson regime to the Rabi
regime, followed by a detection of atoms in internal electronic states.
Decoherence mechanisms are studied in detail promising a high ratio between the
decoherence time and the gate operation time.Comment: 7 figure
Atom loss from Bose-Einstein condensates due to Feshbach resonance
In recent experiments on Na Bose-Einstein condensates [S. Inouye et al,
Nature 392, 151 (1998); J. Stenger et al, Phys. Rev. Lett. 82, 2422 (1999)],
large loss rates were observed when a time-varying magnetic field was used to
tune a molecular Feshbach resonance state near the state of pairs of atoms
belonging to the condensate many-body wavefunction. A mechanism is offered here
to account for the observed losses, based on the deactivation of the resonant
molecular state by interaction with a third condensate atom.Comment: LaTeX, 4 pages, 4 PostScript figures, uses REVTeX and psfig,
submitted to Physical Review A, Rapid Communication
The homotopy theory of simplicial props
The category of (colored) props is an enhancement of the category of colored
operads, and thus of the category of small categories. In this paper, the
second in a series on "higher props," we show that the category of all small
colored simplicial props admits a cofibrantly generated model category
structure. With this model structure, the forgetful functor from props to
operads is a right Quillen functor.Comment: Final version, to appear in Israel J. Mat
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
Local Spin-Gauge Symmetry of the Bose-Einstein Condensates in Atomic Gases
The Bose-Einstein condensates of alkali atomic gases are spinor fields with
local ``spin-gauge" symmetry. This symmetry is manifested by a superfluid
velocity (or gauge field) generated by the Berry phase of the
spin field. In ``static" traps, splits the degeneracy of the
harmonic energy levels, breaks the inversion symmetry of the vortex nucleation
frequency , and can lead to {\em vortex ground states}. The
inversion symmetry of , however, is not broken in ``dynamic"
traps. Rotations of the atom cloud can be generated by adiabatic effects
without physically rotating the entire trap.Comment: Typos in the previous version corrected, thanks to the careful
reading of Daniel L. Cox. 13 pages + 2 Figures in uuencode + gzip for
Kripke Semantics for Martin-L\"of's Extensional Type Theory
It is well-known that simple type theory is complete with respect to
non-standard set-valued models. Completeness for standard models only holds
with respect to certain extended classes of models, e.g., the class of
cartesian closed categories. Similarly, dependent type theory is complete for
locally cartesian closed categories. However, it is usually difficult to
establish the coherence of interpretations of dependent type theory, i.e., to
show that the interpretations of equal expressions are indeed equal. Several
classes of models have been used to remedy this problem. We contribute to this
investigation by giving a semantics that is standard, coherent, and
sufficiently general for completeness while remaining relatively easy to
compute with. Our models interpret types of Martin-L\"of's extensional
dependent type theory as sets indexed over posets or, equivalently, as
fibrations over posets. This semantics can be seen as a generalization to
dependent type theory of the interpretation of intuitionistic first-order logic
in Kripke models. This yields a simple coherent model theory, with respect to
which simple and dependent type theory are sound and complete
Zero-temperature phase diagram of binary boson-fermion mixtures
We calculate the phase diagram for dilute mixtures of bosons and fermions at
zero temperature. The linear stability conditions are derived and related to
the effective boson-induced interaction between the fermions. We show that in
equilibrium there are three possibilities: a) a single uniform phase, b) a
purely fermionic phase coexisting with a purely bosonic one and c) a purely
fermionic phase coexisting with a mixed phase.Comment: 8 pages, revtex, 3 postscript figures; NORDITA-1999/71 C
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