8,483 research outputs found
Phase diagram for a Bose-Einstein condensate moving in an optical lattice
The stability of superfluid currents in a system of ultracold bosons was
studied using a moving optical lattice. Superfluid currents in a very weak
lattice become unstable when their momentum exceeds 0.5 recoil momentum.
Superfluidity vanishes already for zero momentum as the lattice deep reaches
the Mott insulator(MI) phase transition. We study the phase diagram for the
disappearance of superfluidity as a function of momentum and lattice depth
between these two limits. Our phase boundary extrapolates to the critical
lattice depth for the superfluid-to-MI transition with 2% precision. When a
one-dimensional gas was loaded into a moving optical lattice a sudden
broadening of the transition between stable and unstable phases was observed.Comment: 4 figure
About multiplicities and applications to Bezout numbers
Let denote a local Noetherian ring and
an ideal such that for a
finitely generated -module . Let \au = a_1,\ldots,a_d denote a system
of parameters of such that for . It follows that \chi := e_0(\au;M)
- c \cdot e_0(\mathfrak{q};M) \geq 0, where .
The main results of the report are a discussion when resp. to
describe the value of in some particular cases. Applications concern
results on the multiplicity e_0(\au;M) and applications to Bezout numbers.Comment: 11 pages, to appear Springer INdAM-Series, Vol. 20 (2017
Atomic Resonance and Scattering
Contains reports on three research projects.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E
Optical Weak Link between Two Spatially Separate Bose-Einstein Condensates
Two spatially separate Bose-Einstein condensates were prepared in an optical
double-well potential. A bidirectional coupling between the two condensates was
established by two pairs of Bragg beams which continuously outcoupled atoms in
opposite directions. The atomic currents induced by the optical coupling depend
on the relative phase of the two condensates and on an additional controllable
coupling phase. This was observed through symmetric and antisymmetric
correlations between the two outcoupled atom fluxes. A Josephson optical
coupling of two condensates in a ring geometry is proposed. The continuous
outcoupling method was used to monitor slow relative motions of two elongated
condensates and characterize the trapping potential.Comment: 4 pages, 5 figure
Double-impulse magnetic focusing of launched cold atoms.
We have theoretically investigated three-dimensional focusing of a launched cloud of cold atoms using a pair of magnetic lens pulses (the alternate-gradient method). Individual lenses focus radially and defocus axially or vice versa. The performance of the two possible pulse sequences are compared and found to be ideal for loading both 'pancake' and 'sausage' shaped magnetic/optical microtraps. It is shown that focusing aberrations are considerably smaller for double-impulse magnetic lenses compared to single-impulse magnetic lenses. An analysis of clouds focused by the double-impulse technique is presented
Low velocity quantum reflection of Bose-Einstein condensates
We studied quantum reflection of Bose-Einstein condensates at normal
incidence on a square array of silicon pillars. For incident velocities of
2.5-26 mm/s observations agreed with theoretical predictions that the
Casimir-Polder potential of a reduced density surface would reflect slow atoms
with much higher probability. At low velocities (0.5-2.5 mm/s), we observed
that the reflection probability saturated around 60% rather than increasing
towards unity. We present a simple model which explains this reduced
reflectivity as resulting from the combined effects of the Casimir-Polder plus
mean field potential and predicts the observed saturation. Furthermore, at low
incident velocities, the reflected condensates show collective excitations.Comment: 4 figure
Atomic Resonance and Scattering
Contains research objectives and reports on one research project.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 28-043-AMC-02536(E)U.S. Navy (Office of Naval Research) under Contract N00014-67-A-0204-0006Sloan Fund for Basic Research (M. I. T. Grant 170
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