41 research outputs found
Free expansion of a Bose-Einstein condensate at the presence of a thermal cloud
We investigate numerically the free-fall expansion of a Rb atoms
condensate at nonzero temperatures. The classical field approximation is used
to separate the condensate and the thermal cloud during the expansion. We
calculate the radial and axial widths of the expanding condensate and find
clear evidence that the thermal component changes the dynamics of the
condensate. Our results are confronted against the experimental data
Ground state of two-component degenerate fermionic gases
We analyze the ground state of the two--component gas of trapped ultracold
fermionic atoms. We neglect the forces between atoms in the same hyperfine
state (the same component). For the case when the forces between
distinguishable atoms (i.e., atoms in different hyperfine states) are repulsive
(positive mutual scattering length), we find the existence of critical
interaction strength above which one atomic fraction expels the other from the
center of the trap. When atoms from different components attract each other
(negative mutual scattering length) the ground state of the system dramatically
changes its structure for strong enough attraction -- the Cooper pairs built of
atoms in different hyperfine states appear.Comment: 10 pages, 14 figure
Two component Bose-Hubbard model with higher angular momentum states
We study a Bose-Hubbard Hamiltonian of ultracold two component gas of spinor
Chromium atoms. Dipolar interactions of magnetic moments while tuned resonantly
by ultralow magnetic field can lead to spin flipping. Due to approximate axial
symmetry of individual lattice site, total angular momentum is conserved.
Therefore, all changes of the spin are accompanied by the appearance of the
angular orbital momentum. This way excited Wannier states with non vanishing
angular orbital momentum can be created. Resonant dipolar coupling of the two
component Bose gas introduces additional degree of control of the system, and
leads to a variety of different stable phases. The phase diagram for small
number of particles is discussed.Comment: 4 pages, 2 figure
Decay of multiply charged vortices at nonzero temperatures
We study the instability of multiply charged vortices in the presence of
thermal atoms and find various scenarios of splitting of such vortices. The
onset of the decay of a vortex is always preceded by the increase of a number
of thermal (uncondensed) atoms in the system and manifests itself by the sudden
rise of the amplitude of the oscillations of the quadrupole moment. Our
calculations show that the decay time gets shorter when the multiplicity of a
vortex becomes higher.Comment: 4 pages, 6 figure
On the stability of Bose-Fermi mixtures
We consider the stability of a mixture of degenerate Bose and Fermi gases.
Even though the bosons effectively repel each other the mixture can still
collapse provided the Bose and Fermi gases attract each other strongly enough.
For a given number of atoms and the strengths of the interactions between them
we find the geometry of a maximally compact trap that supports the stable
mixture. We compare a simple analytical estimation for the critical axial
frequency of the trap with results based on the numerical solution of
hydrodynamic equations for Bose-Fermi mixture.Comment: 4 pages, 3 figure
Statistical properties of one dimensional attractive Bose gas
Using classical field approximation we present the first study of statistical
properties of one dimensional Bose gas with attractive interaction. The
canonical probability distribution is generated with the help of a Monte Carlo
method. This way we obtain not only the depletion of the condensate with
growing temperature but also its fluctuations. The most important is our
discovery of a reduced coherence length, the phenomenon observed earlier only
for the repulsive gas, known as quasicondensation.Comment: 4 pages, 4 figure