32,144 research outputs found
Dynamical Response of Fermi Condensate to Varying Magnetic Fields
We investigate the dynamical response of strongly interacting ultra-cold
fermionic atoms near Feshbach resonance to varying magnetic fields. Following
the experimental practices, we calculate the response of the atoms to
oscillating and to linearly ramped magnetic fields respectively. For
oscillating magnetic fields, depending on the frequencies and the amplitudes of
the oscillations, the response of the pair excitation gap shows either linear
or rich non-linear behaviour. In addition, both the spectral studies through
the linear response theory and the time-domain simulations suggest the
existence of a resonant frequency corresponding to the pair dissociation
threshold. For linearly ramped magnetic fields, the response of the excitation
gap shows damped oscillations. The final value of the excitation gap depends on
the rate of the field sweep.Comment: 6 pages, 6 figure
Superfluid shells for trapped fermions with mass and population imbalance
We map out the phase diagram of strongly interacting fermions in a potential
trap with mass and population imbalance between the two spin components. As a
unique feature distinctively different from the equal-mass case, we show that
the superfluid here forms a shell structure which is not simply connected in
space. Different types of normal states occupy the trap regions inside and
outside this superfluid shell. We calculate the atomic density profiles, which
provide an experimental signature for the superfluid shell structure.Comment: 4 pages, 3 figure
Detecting the breached pair phase in a polarized ultracold Fermi gas
We propose a method for the experimental detection of a new quantum phase,
the breached pair state, in a strongly interacting ultracold Fermi gas with
population imbalance. We show that through the time-of-flight Raman imaging,
the presence of such a phase can be unambiguously determined with a measurement
of the momentum-space phase separation of the minority spin component. To guide
the experimental efforts, the momentum-space density profiles are calculated
under typical experimental conditions.Comment: 4 pages, 3 figures, replaced with the published versio
Trapped Fermions across a Feshbach resonance with population imbalance
We investigate the phase separation of resonantly interacting fermions in a
trap with imbalanced spin populations, both at zero and at finite temperatures.
We directly minimize the thermodynamical potential under the local density
approximation instead of using the gap equation, as the latter may give
unstable solutions. On the BEC side of the resonance, one may cross three
different phases from the trap center to the edge; while on the BCS side or at
resonance, typically only two phases show up. We compare our results with the
recent experiment, and the agreement is remarkable.Comment: 4 pages, 3 figures, replaced with the published versio
BCS-BEC crossover and quantum phase transition for 6Li and 40K atoms across Feshbach resonance
We systematically study the BCS-BEC crossover and the quantum phase
transition in ultracold 6Li and 40K atoms across a wide Feshbach resonance. The
background scattering lengths for 6Li and 40K have opposite signs, which lead
to very different behaviors for these two types of atoms. For 40K, both the
two-body and the many-body calculations show that the system always has two
branches of solutions: one corresponds to a deeply bound molecule state; and
the other, the one accessed by the current experiments, corresponds to a weakly
bound state with population always dominantly in the open channel. For 6Li,
there is only a unique solution with the standard crossover from the weakly
bound Cooper pairs to the deeply bound molecules as one sweeps the magnetic
field through the crossover region. Because of this difference, for the
experimentally accessible state of 40K, there is a quantum phase transition at
zero temperature from the superfluid to the normal fermi gas at the positive
detuning of the magnetic field where the s-wave scattering length passes its
zero point. For 6Li, however, the system changes continuously across the zero
point of the scattering length. For both types of atoms, we also give detailed
comparison between the results from the two-channel and the single-channel
model over the whole region of the magnetic field detuning.Comment: 7 pages, 6 figure
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