12,352 research outputs found
A solvable model of a one-dimensional quantum gas with pair interaction
We propose a solvable model of a one-dimensional harmonic oscillator quantum
gas of two sorts of particles, fermions or bosons, which allows to describe the
formation of pairs due to a suitable pair interaction. These pairs we call
"pseudo-bosons" since the system can be approximated by an ideal bose gas for
low temperatures. We illustrate this fact by considering the specific heat and
the entropy function for N=8 pairs. The model can also be evaluated in the
thermodynamic limit if the harmonic oscillator potential is suitable scaled
Thermodynamic fermion-boson symmetry in harmonic oscillator potentials
A remarkable thermodynamic fermion-boson symmetry is found for the canonical
ensemble of ideal quantum gases in harmonic oscillator potentials of odd
dimensions. The bosonic partition function is related to the fermionic one
extended to negative temperatures, and vice versa.Comment: 7 pages, no figures, submitted to PHYSICA A. More information
available at http://www.physik.uni-osnabrueck.de/makrosysteme
Suppression of Kelvon-induced decay of quantized vortices in oblate Bose-Einstein Condensates
We study the Kelvin mode excitations on a vortex line in a three-dimensional
trapped Bose-Einstein condensate at finite temperature. Our stochastic
Gross-Pitaevskii simulations show that the activation of these modes can be
suppressed by tightening the confinement along the direction of the vortex
line, leading to a strong suppression in the vortex decay rate as the system
enters a regime of two-dimensional vortex dynamics. As the system approaches
the condensation transition temperature we find that the vortex decay rate is
strongly sensitive to dimensionality and temperature, observing a large
enhancement for quasi-two-dimensional traps. Three-dimensional simulations of
the recent vortex dipole decay experiment of Neely et al. [Phys. Rev. Lett.
104, 160401 (2010)] confirm two-dimensional vortex dynamics, and predict a
dipole lifetime consistent with experimental observations and suppression of
Kelvon-induced vortex decay in highly oblate condensates.Comment: 8 pages, 8 figure
Investigations on finite ideal quantum gases
Recursion formulae of the N-particle partition function, the occupation
numbers and its fluctuations are given using the single-particle partition
function. Exact results are presented for fermions and bosons in a common
one-dimensional harmonic oscillator potential, for the three-dimensional
harmonic oscillator approximations are tested. Applications to excited nuclei
and Bose-Einstein condensation are discussed.Comment: 13 pages, 7 postscript figures, uses 'epsfig.sty'. Submitted to
Physica A. More information available at
http://obelix.physik.uni-osnabrueck.de/~schnack
Coherent resonant interactions and slow light with molecules confined in photonic band-gap fibers
We investigate resonant nonlinear optical interactions and demonstrate
induced transparency in acetylene molecules in a hollow-core photonic band-gap
fiber at 1.5m. The induced spectral transmission window is used to
demonstrate slow-light effects, and we show that the observed broadening of the
spectral features is due to collisions of the molecules with the inner walls of
the fiber core. Our results illustrate that such fibers can be used to
facilitate strong coherent light-matter interactions even when the optical
response of the individual molecules is weak.Comment: 5 pages, 4 figure
Bose-Einstein condensation of chromium
We report on the generation of a Bose-Einstein condensate in a gas of
chromium atoms, which will make studies of the effects of anisotropic
long-range interactions in degenerate quantum gases possible. The preparation
of the chromium condensate requires novel cooling strategies that are adapted
to its special electronic and magnetic properties. The final step to reach
quantum degeneracy is forced evaporative cooling of 52Cr atoms within a crossed
optical dipole trap. At a critical temperature of T~700nK, we observe
Bose-Einstein condensation by the appearance of a two-component velocity
distribution. Released from an anisotropic trap, the condensate expands with an
inversion of the aspect ratio. We observe critical behavior of the condensate
fraction as a function of temperature and more than 50,000 condensed 52Cr
atoms.Comment: 4 pages, 4 figure
Collisional Properties of Cold Spin-Polarized Metastable Neon Atoms
We measure the rates of elastic and inelastic two-body collisions of cold
spin-polarized neon atoms in the metastable 3P2 state for 20^Ne and 22^Ne in a
magnetic trap. From particle loss, we determine the loss parameter of inelastic
collisions beta=6.5(18)x10^{-12} cm^3s^{-1} for 20^Ne and
beta=1.2(3)x10^{-11}cm^3{s}^{-1} for 22^Ne. These losses are caused by ionizing
(i.e. Penning) collisions %to more than and occur less frequently than for
unpolarized atoms. This proves the suppression of Penning ionization due to
spin-polarization. From cross-dimensional relaxation measurements, we obtain
elastic scattering lengths of a=-180(40) a_0 for 20^Ne and a=+150(+80/-50) a_0
for 22^Ne, where a_0=0.0529 nm.Comment: 4 pages, 3 figure
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