1,570 research outputs found
Spin diffusion in trapped clouds of strongly interacting cold atoms
We show that puzzling recent experimental results on spin diffusion in a
strongly interacting atomic gas may be understood in terms of the predicted
spin diffusion coefficient for a generic strongly interacting system. Three
important features play a central role: a) Fick's law for diffusion must be
modified to allow for the trapping potential, b) the diffusion coefficient is
inhomogeneous, due to the density variations in the cloud and c) the diffusion
approximation fails in the outer parts of the cloud, where the mean free path
is long.Comment: 4 pages, 6 figures, minor modifications to the text and figures in 2.
versio
Effects of the trapping potential on a superfluid atomic Fermi Gas
We examine a dilute two-component atomic Fermi gas trapped in a harmonic
potential in the superfluid phase. For experimentally realistic parameters, the
trapping potential is shown to have crucial influence on various properties of
the gas. Using an effective hamiltonian, analytical results for the critical
temperature, the temperature dependence of the superfluid gap, and the energy
of the lowest collective modes are derived. These results are shown to agree
well with numerical calculations. We furthermore discuss in more detail a
previous proposed method to experimentally observe the superfluid transition by
looking at the collective mode spectrum. Our results are aimed at the present
experimental effort to observe a superfluid phase transition in a trapped
atomic Fermi gas.Comment: 2. revised version. Minor mistakes in equation references corrected.
To appear in Phys. Rev.
An effective theory of Feshbach resonances and many-body properties of Fermi gases
For calculating low-energy properties of a dilute gas of atoms interacting
via a Feshbach resonance, we develop an effective theory in which the
parameters that enter are an atom-molecule coupling strength and the magnetic
moment of the molecular resonance. We demonstrate that for resonances in the
fermionic systems Li and K that are under experimental
investigation, the coupling is so strong that many-body effects are appreciable
even when the resonance lies at an energy large compared with the Fermi energy.
We calculate a number of many-body effects, including the effective mass and
the lifetime of atomic quasiparticles in the gas.Comment: 4 pages, 1 figure, NORDITA-2003-21 C
Using superlattice potentials to probe long-range magnetic correlations in optical lattices
In Pedersen et al. (2011) we proposed a method to utilize a temporally
dependent superlattice potential to mediate spin-selective transport, and
thereby probe long and short range magnetic correlations in optical lattices.
Specifically this can be used for detecting antiferromagnetic ordering in
repulsive fermionic optical lattice systems, but more generally it can serve as
a means of directly probing correlations among the atoms by measuring the mean
value of an observable, the number of double occupied sites. Here, we provide a
detailed investigation of the physical processes which limit the effectiveness
of this "conveyer belt method". Furthermore we propose a simple ways to improve
the procedure, resulting in an essentially perfect (error-free) probing of the
magnetic correlations. These results shows that suitably constructed
superlattices constitute a promising way of manipulating atoms of different
spin species as well as probing their interactions.Comment: 12 pages, 9 figure
Bragg Spectroscopy of Cold Atomic Fermi Gases
We propose a Bragg spectroscopy experiment to measure the onset of superfluid
pairing in ultracold trapped Fermi gases. In particular, we study two component
Fermi gases in the weak coupling BCS and BEC limits as well as in the strong
coupling unitarity limit. The low temperature Bragg spectrum exhibits a gap
directly related to the pair-breaking energy. Furthermore, the Bragg spectrum
has a large maximum just below the critical temperature when the gas is
superfluid in the BCS limit. In the unitarity regime, we show how the pseudogap
in the normal phase leads to a significant suppression of the low frequency
Bragg spectrum.Comment: 8 pages, 9 figures. Typos corrected. Reference update
Twin peaks in rf spectra of Fermi gases at unitarity
We calculate the radio-frequency spectrum of balanced and imbalanced
ultracold Fermi gases in the normal phase at unitarity.
For the homogeneous case the spectrum of both the majority and minority
components always has a single peak even in the pseudogap regime.
We furthermore show how the double-peak structures observed in recent
experiments arise due to the inhomogeneity of the trapped gas.
The main experimental features observed above the critical temperature in the
recent experiment of Schunck et al. [Science 316, 867, (2007)] are recovered
with no fitting parameters.Comment: v3: version accepted for publication as a Rapid Communication in PRA.
With respect to v2, minor changes in the text and in the inset of Fig.
Self-bound many-body states of quasi-one-dimensional dipolar Fermi gases: Exploiting Bose-Fermi mappings for generalized contact interactions
Using a combination of results from exact mappings and from mean-field theory
we explore the phase diagram of quasi-one-dimensional systems of identical
fermions with attractive dipolar interactions. We demonstrate that at low
density these systems provide a realization of a single-component
one-dimensional Fermi gas with a generalized contact interaction. Using an
exact duality between one-dimensional Fermi and Bose gases, we show that when
the dipole moment is strong enough, bound many-body states exist, and we
calculate the critical coupling strength for the emergence of these states. At
higher densities, the Hartree-Fock approximation is accurate, and by combining
the two approaches we determine the structure of the phase diagram. The
many-body bound states should be accessible in future experiments with
ultracold polar molecules
Low energy monopole Modes of a Trapped atomic Fermi Gas
We consider the low energy collective monopole modes of a trapped weakly
interacting atomic Fermi gas in the collisionless regime. The spectrum is
calculated for varying coupling strength and chemical potential. Using an
effective Hamiltonian, we derive analytical results that agree well with
numerical calculations in various regimes. The onset of superfluidity is shown
to lead to effects such as the vanishing of the energy required to create a
Cooper molecule at a critical coupling strength and to the emergence of pair
vibration excitations. Our analysis suggests ways to experimentally detect the
presence of the superfluid phase in trapped atomic Fermi gases.Comment: 5 pages & 1 figure. Accepted for Phys. Rev. Let
Laser probing of Cooper-paired trapped atoms
We consider a gas of trapped Cooper-paired fermionic atoms which are
manipulated by laser light. The laser induces a transition from an internal
state with large negative scattering length (superfluid) to one with weaker
interactions (normal gas). We show that the process can be used to detect the
presence of the superconducting order parameter. Also, we propose a direct way
of measuring the size of the gap in the trap. The efficiency and feasibility of
this probing method is investigated in detail in different physical situations.Comment: 9 pages, 8 figure
- …