60 research outputs found
Landau Damping of Spin Waves in Trapped Boltzmann Gases
A semiclassical method is used to study Landau damping of transverse
pseudo-spin waves in harmonically trapped ultracold gases in the collisionless
Boltzmann limit. In this approach, the time evolution of a spin is calculated
numerically as it travels in a classical orbit through a spatially dependent
mean field. This method reproduces the Landau damping results for spin-waves in
unbounded systems obtained with a dielectric formalism. In trapped systems, the
simulations indicate that Landau damping occurs for a given spin-wave mode
because of resonant phase space trajectories in which spins are "kicked out" of
the mode (in spin space). A perturbative analysis of the resonant and nearly
resonant trajectories gives the Landau damping rate, which is calculated for
the dipole and quadrupole modes as a function of the interaction strength. The
results are compared to a numerical solution of the kinetic equation by Nikuni
et al.Comment: 6 pages, 2 figure
A pulsed, low-temperature beam of supersonically cooled free radical OH molecules
An improved system for creating a pulsed, low-temperature molecular beam of
OH radicals has been developed. We use a pulsed discharge to create OH from
HO seeded in Xe during a supersonic expansion, where the high-voltage pulse
duration is significantly shorter than the width of the gas pulse. The pulsed
discharge allows for control of the mean speed of the molecular packet as well
as maintains a low temperature supersonic expansion. A hot filament is placed
in the source chamber to initiate the discharge for shorter durations and at
lower voltages, resulting in a translationally and rotationally colder packet
of OH molecules
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Drift waves in stellarator geometry
Drift waves are investigated in a real three-dimensional stellarator geometry. A linear system, based on the cold ion fluid model and a ballooning mode formalism, is solved numerically in the geometry of the stellarator H1-NF. The spectra of stable and unstable modes, as well as localization, are discussed. The dependence of the spectrum of the unstable modes on the wavevector, plasma density variation, and the location in the plasma is presented
Detecting Super-Counter-Fluidity by Ramsey Spectroscopy
Spatially selective Ramsey spectroscopy is suggested as a method for
detecting the super-counter-fluidity of two-component atomic mixture in optical
lattice.Comment: 3pages, no figures, replaced with revised version accepted by PRA.
Discussion of the Ramsey pattern specific for topological excitations is
adde
Spin dynamics of a trapped spin-1 Bose Gas above the Bose-Einstein transition temperature
We study collective spin oscillations in a spin-1 Bose gas above the
Bose-Einstein transition temperature. Starting from the Heisenberg equation of
motion, we derive a kinetic equation describing the dynamics of a thermal gas
with the spin-1 degree of freedom. Applying the moment method to the kinetic
equation, we study spin-wave collective modes with dipole symmetry. The dipole
modes in the spin-1 system are found to be classified into the three type of
modes. The frequency and damping rate are obtained as functions of the peak
density. The damping rate is characterized by three relaxation times associated
with collisions.Comment: 19 pages, 5 figur
Castaing Instability and Precessing Domains in Confined Alkali Gases
We explore analogy between two-component quantum alkali gases and
spin-polarized helium systems. Recent experiments in trapped gases are put into
the frame of the existing theory for Castaing instability in transverse channel
and formation of homogeneous precessing domains in spin-polarized systems.
Analogous effects have already been observed in spin-polarized and
mixtures systems. The threshold effect of the confining
potential on the instability is analyzed. New experimental possibilities for
observation of transverse instability in a trap are discussed.Comment: 6 RevTex pages, no figure
A slow gravity compensated Atom Laser
We report on a slow guided atom laser beam outcoupled from a Bose-Einstein
condensate of 87Rb atoms in a hybrid trap. The acceleration of the atom laser
beam can be controlled by compensating the gravitational acceleration and we
reach residual accelerations as low as 0.0027 g. The outcoupling mechanism
allows for the production of a constant flux of 4.5x10^6 atoms per second and
due to transverse guiding we obtain an upper limit for the mean beam width of
4.6 \mu\m. The transverse velocity spread is only 0.2 mm/s and thus an upper
limit for the beam quality parameter is M^2=2.5. We demonstrate the potential
of the long interrogation times available with this atom laser beam by
measuring the trap frequency in a single measurement. The small beam width
together with the long evolution and interrogation time makes this atom laser
beam a promising tool for continuous interferometric measurements.Comment: 7 pages, 8 figures, to be published in Applied Physics
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