660 research outputs found
Noise Correlations in one-dimensional systems of ultra-cold fermions
Time of flight images reflect the momentum distribution of the atoms in the
trap, but the spatial noise in the image holds information on more subtle
correlations. Using Bosonization, we study such noise correlations in generic
one dimensional systems of ultra cold fermions. Specifically, we show how
pairing as well as spin and charge density wave correlations may be identified
and extracted from the time of flight images. These incipient orders manifest
themselves as power law singularities in the noise correlations, that depend on
the Luttinger parameters, which suggests a general experimental technique to
obtain them.Comment: 5 pages, 3 figures. Added discussion on the visibility of noise
correlation features for realistic condition
Commensurate mixtures of ultra-cold atoms in one dimension
We study binary mixtures of ultra-cold atoms, confined to one dimension in an
optical lattice, with commensurate densities. Within a Luttinger liquid
description, which treats various mixtures on equal footing, we derive a system
of renormalization group equations at second order, from which we determine the
rich phase diagrams of these mixtures. These phases include charge/spin density
wave order, singlet and triplet pairing, polaron pairing, and a supersolid
phase. Various methods to detect our results experimentally are discussed.Comment: 7 pages, 4 figures, v4: extended versio
Decay of a superfluid current of ultra-cold atoms in a toroidal trap
Using a numerical implementation of the truncated Wigner approximation, we
simulate the experiment reported by Ramanathan et al. in Phys. Rev. Lett. 106,
130401 (2011), in which a Bose-Einstein condensate is created in a toroidal
trap and set into rotation via a phase imprinting technique. A potential
barrier is then placed in the trap to study the decay of the superflow. We find
that the current decays via thermally activated phase slips, which can also be
visualized as vortices crossing the barrier region in the radial direction.
Adopting the notion of critical velocity used in the experiment, we determine
it to be lower than the local speed of sound at the barrier, in contradiction
to the predictions of the zero-temperature Gross-Pitaevskii equation. We map
out the superfluid decay rate and critical velocity as a function of
temperature and observe a strong dependence. Thermal fluctuations offer a
partial explanation of the experimentally observed reduction of the critical
velocity from the phonon velocity.Comment: 15 pages. 11 figure
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