251 research outputs found
Laser probing of atomic Cooper pairs
We consider a gas of attractively interacting cold Fermionic atoms which are
manipulated by laser light. The laser induces a transition from an internal
state with large negative scattering length to one with almost no interactions.
The process can be viewed as a tunneling of atomic population between the
superconducting and the normal states of the gas. It can be used to detect the
BCS-ground state and to measure the superconducting order parameter.Comment: 4 pages, 2 figure
Effect of wavelength dependence of nonlinearity, gain, and dispersion in photonic crystal fiber amplifiers
Photonic crystal fibers are used in fiber amplifiers and lasers because of
the flexibility in the design of mode area and dispersion. However, these
quantities depend strongly on the wavelength. The wavelength dependence of
gain, nonlinearity and dispersion are investigated here by including the
wavelength dependence explicitly in the nonlinear Schr\"odinger equation for
photonic crystal fibers with varying periods and hole sizes. The effect of the
wavelength dependence of each parameter is studied separately as well as
combined. The wavelength dependence of the parameters is shown to create
asymmetry to the spectrum and chirp, but to have a moderating effect on pulse
broadening. The effect of including the wavelength dependence of nonlinearity
in the simulations is demonstrated to be the most significant compared that of
dispersion or gain
Pairing in a three component Fermi gas
We consider pairing in a three-component gas of degenerate fermions. In
particular, we solve the finite temperature mean-field theory of an interacting
gas for a system where both interaction strengths and fermion masses can be
unequal. At zero temperature we find a a possibility of a quantum phase
transition between states associated with pairing between different pairs of
fermions. On the other hand, finite temperature behavior of the three-component
system reveals some qualitative differences from the two-component gas: for a
range of parameters it is possible to have two different critical temperatures.
The lower one corresponds to a transition between different pairing channels,
while the higher one corresponds to the usual superfluid-normal transition. We
discuss how these phase transitions could be observed in ultracold gases of
fermionic atoms.Comment: 10 pages, 3 figure
Pairing gap and in-gap excitations in trapped fermionic superfluids
We consider trapped atomic Fermi gases with Feshbach-resonance enhanced
interactions in pseudogap and superfluid temperatures. We calculate the
spectrum of RF(or laser)-excitations for transitions that transfer atoms out of
the superfluid state. The spectrum displays the pairing gap and also the
contribution of unpaired atoms, i.e. in-gap excitations. The results support
the conclusion that a superfluid, where pairing is a many-body effect, was
observed in recent experiments on RF spectroscopy of the pairing gap.Comment: Journal versio
Strongly interacting Fermi gases with density imbalance
We consider density-imbalanced Fermi gases of atoms in the strongly
interacting, i.e. unitarity, regime. The Bogoliubov-deGennes equations for a
trapped superfluid are solved. They take into account the finite size of the
system, as well as give rise to both phase separation and FFLO type
oscillations in the order parameter. We show how radio-frequency spectroscopy
reflects the phase separation, and can provide direct evidence of the FFLO-type
oscillations via observing the nodes of the order parameter.Comment: Added one reference. Published in PR
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