199 research outputs found
Images of a Bose-Einstein condensate in position and momentum space
In the Bogoliubov theory a condensate initially prepared in its ground state
described by stationary Bogoliubov vacuum and later perturbed by a
time-dependent potential or interaction strength evolves into a time-dependent
excited state which is dynamical Bogoliubov vacuum. The dynamical vacuum has a
simple diagonal form in a time-dependent orthonormal basis of single particle
modes. This diagonal representation leads to a gaussian probability
distribution for possible outcomes of density measurements in position and
momentum space. In these notes we also discuss relations with the U(1) symmetry
breaking version of the Bogoliubov theory and give two equivalent gaussian
integral representations of the dynamical vacuum state.Comment: 4 pages; Talk given at the Laser Physics Workshop, July 2005, Kyoto,
Japa
Einstein-Infeld-Hoffman method and soliton dynamics in a parity noninvariant system
We consider slow motion of a pointlike topological defect (vortex) in the
nonlinear Schrodinger equation minimally coupled to Chern-Simons gauge field
and subject to external uniform magnetic field. It turns out that a formal
expansion of fields in powers of defect velocity yields only the trivial static
solution. To obtain a nontrivial solution one has to treat velocities and
accelerations as being of the same order. We assume that acceleration is a
linear form of velocity. The field equations linearized in velocity uniquely
determine the linear relation. It turns out that the only nontrivial solution
is the cyclotron motion of the vortex together with the whole condensate. This
solution is a perturbative approximation to the center of mass motion known
from the theory of magnetic translations.Comment: 6 pages in Latex; shortened version to appear in Phys.Rev.
Interference of Fock states in a single measurement
We study analytically the structure of an arbitrary order correlation
function for a pair of Fock states and prove without any approximations that in
a single measurement of particle positions interference effects must occur as
experimentally observed with Bose-Einstein condensates. We also show that the
noise level present in the statistics is slightly lower than for a respective
measurement of phase states.Comment: 4 page
More on scattering of Chern-Simons vortices
I derive a general formalism for finding kinetic terms of the effective
Lagrangian for slowly moving Chern-Simons vortices. Deformations of fields
linear in velocities are taken into account. From the equations they must
satisfy I extract the kinetic term in the limit of coincident vortices. For
vortices passing one over the other there is locally the right-angle
scattering. The method is based on analysis of field equations instead of
action functional so it may be useful also for nonvariational equations in
nonrelativistic models of Condensed Matter Physics.Comment: discussion around Eq.(45) is generalised, one more condition for the
local right-angle scattering is adde
Laser cooling all the way down to molecular condensate
Numerical simulations show that laser cooling of fermions on the repulsive
side of the Feshbach resonance can sympathetically cool molecules well below
their condensation temperature.Comment: 7 pages, 2 .eps figure
Optimal cooling strategies for magnetically trapped atomic Fermi-Bose mixtures
We discuss cooling efficiency for different-species Fermi-Bose mixtures in
magnetic traps. A better heat capacity matching between the two atomic species
is achieved by a proper choice of the Bose cooler and the magnetically
trappable hyperfine states of the mixture. When a partial spatial overlap
between the two species is also taken into account, the deepest Fermi
degeneracy is obtained for an optimal value of the trapping frequency ratio.
This can be achieved by assisting the magnetic trap with a deconfining light
beam, as shown in the case of fermionic 6Li mixed with 23Na, 87Rb, and 133Cs,
with optimal conditions found for the not yet explored 6Li-87Rb mixture.Comment: 5 pages, 3 figures, to appear in Physical Review
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