619 research outputs found
Counterflow in a doubly superfluid mixture of Bosons and Fermions
In this article, we calculate the friction between two counter-flowing
bosonic and fermionic super-fluids. In the limit where the boson-boson and
boson-fermion interactions can be treated within the mean-field approximation,
we show that the force can be related to the dynamical structure factor of the
fermionic component. Finally, we provide asymptotic expressions for weakly and
strongly attractive fermions and show that the damping rate obeys simple
scaling laws close to the critical velocity.Comment: Submitted to Phys. Rev.
Universal phase diagram of a strongly interacting Fermi gas with unbalanced spin populations
We present a theoretical interpretation of a recent experiment presented in
ref. \cite{Zwierlein06} on the density profile of Fermi gases with unbalanced
spin populations. We show that in the regime of strong interaction, the
boundaries of the three phases observed in \cite{Zwierlein06} can be
characterized by two dimensionless numbers and .
Using a combination of a variational treatment and a study of the experimental
results, we infer rather precise bounds for these two parameters.Comment: 4 pages, 2 figure
The normal phase of an imbalanced Fermi gas
Recent experiments on imbalanced Fermi gases have raised interest in the
physics of an impurity immersed in a Fermi sea, the so-called Fermi polaron. In
this letter, a simple theory is devised to describe dilute Fermi-polaron
ensembles corresponding to the normal phase of an imbalanced Fermi gas. An
exact formula is obtained for the dominant interaction between polarons,
expressed solely in terms of a single polaron parameter. The physics of this
interaction is identified as a signature of the Pauli exclusion principle.Comment: 4 pages, 2 figures, published in PR
Capillary-gravity waves: a "fixed-depth" analysis
We study the onset of the wave-resistance due to the generation of
capillary-gravity waves by a partially immersed moving object in the case where
the object is hold at a fixed immersion depth. We show that, in this case, the
wave resistance varies continuously with the velocity, in qualitative
accordance with recent experiments by Burghelea et al. (Phys. Rev. Lett. 86,
2557 (2001)).Comment: 7 pages, 3 figures, submitted to Europhysics Letter
Few vs many-body physics of an impurity immersed in a superfluid of spin 1/2 attractive fermions
In this article we investigate the properties of an impurity immersed in a
superfluid of strongly correlated spin 1/2 fermions. For resonant interactions,
we first relate the stability diagram of dimer and trimer states to the
three-body problem for an impurity interacting with a pair of fermions. Then we
calculate the beyond-mean-field corrections to the energy of a weakly
interacting impurity. We show that these corrections are divergent and have to
be regularized by properly accounting for three-body physics in the problem
Momentum distribution of a dilute unitary Bose gas with three-body losses
Using Boltzmann's equation, we study the effect of three-body losses on the
momentum distribution of a homogeneous unitary Bose gas in the dilute limit
where quantum correlations are negligible. We calculate the momentum
distribution of the gas and show that inelastic collisions are quantitatively
as important as a second order virial correction.Comment: 4 pages + supplemental materia
Hydrodynamic spectrum of a superfluid in an elongated trap
--In this article we study the hydrodynamic spectrum of a superfluid confined
in a cylindrical trap. We show that the dispersion relation (q) of the
phonon branch scales like \sqrt q at large q, leading to a vanishingly small
superfluid critical velocity. In practice the critical velocity is set by the
breakdown of the hydrodynamic approximation. For a broad class of superfluids,
this entails a reduction of the critical velocity by a factor (
/\"i1/2c) 1/3 with respect to the free-space prediction (here
is the trapping frequency and \"i1/2c the chemical potential of the cloud)
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