480 research outputs found
Effective s- and p-Wave Contact Interactions in Trapped Degenerate Fermi Gases
The structure and stability of dilute degenerate Fermi gases trapped in an
external potential is discussed with special emphasis on the influence of s-
and p-wave interactions. In a first step an Effective Contact Interaction for
all partial waves is derived, which reproduces the energy spectrum of the full
potential within a mean-field model space. Using the s- and p-wave part the
energy density of the multi-component Fermi gas is calculated in Thomas-Fermi
approximation. On this basis the stability of the one- and two-component Fermi
gas against mean-field induced collapse is investigated. Explicit stability
conditions in terms of density and total particle number are given. For the
single-component system attractive p-wave interactions limit the density of the
gas. In the two-component case a subtle competition of s- and p-wave
interactions occurs and gives rise to a rich variety of phenomena. A repulsive
p-wave part, for example, can stabilize a two-component system that would
otherwise collapse due to an attractive s-wave interaction. It is concluded
that the p-wave interaction may have important influence on the structure of
degenerate Fermi gases and should not be discarded from the outset.Comment: 18 pages, 11 figures (using RevTEX4
Superfluidity in the interior-gap states
We investigate superfluidity in the interior-gap states proposed by Liu and
Wilczek. At weak coupling, we find the {\em gapless} interior-gap state
unstable in physically accessible regimes of the parameter space, where the
superfluid density is shown to be always negative. We therefore conclude that
the spatially-uniform interior-gap phase is extremely unstable unless it is
fully gapped; in this case, however, the state is rather similar to
conventional BCS states.Comment: To appear in Physical Review
Two-species magneto-optical trap with 40K and 87Rb
We trap and cool a gas composed of 40K and 87Rb, using a two-species
magneto-optical trap (MOT). This trap represents the first step towards cooling
the Bose-Fermi mixture to quantum degeneracy. Laser light for the MOT is
derived from laser diodes and amplified with a single high power semiconductor
amplifier chip. The four-color laser system is described, and the
single-species and two-species MOTs are characterized. Atom numbers of 1x10^7
40K and 2x10^9 87Rb are trapped in the two-species MOT. Observation of trap
loss due to collisions between species is presented and future prospects for
the experiment are discussed.Comment: 4 pages, 4 figures; accepted for publication in Physical Review
Light guiding light: Nonlinear refraction in rubidium vapor
Recently there has been experimental and theoretical interest in cross-dispersion effects in rubidium vapor, which allows one beam of light to be guided by another. We present theoretical results which account for the complications created by the D line hyperfine structure of rubidium as well as the presence of the two major isotopes of rubidium. This allows the complex frequency dependence of the effects observed in our experiments to be understood and lays the foundation for future studies of nonlinear propagation
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.
Spectroscopic Temperature Determination of Degenerate Fermi Gases
We suggest a simple method for measuring the temperature of ultra-cold gases
made of fermions. We show that by using a two-photon Raman probe, it is
possible to obtain lineshapes which reveal properties of the degenerate sample,
notably its temperature . The proposed method could be used with identical
fermions in different hyperfine states interacting via s-wave scattering or
identical fermions in the same hyperfine state via p-wave scattering. We
illustrate the applicability of the method in realistic conditions for Li
prepared in two different hyperfine states. We find that temperatures down to
0.05 can be determined by this {\it in-situ} method.Comment: 7 pages, 4 figures, Revtex
Degenerate fermion gas heating by hole creation
Loss processes that remove particles from an atom trap leave holes behind in
the single particle distribution if the trapped gas is a degenerate fermion
system. The appearance of holes increases the temperature and we show that the
heating is (i) significant if the initial temperature is well below the Fermi
temperature , and (ii) increases the temperature to
after half of the system's lifetime, regardless of the initial temperature. The
hole heating has important consequences for the prospect of observing
Cooper-pairing in atom traps.Comment: to be published in PR
Spin Excitations in a Fermi Gas of Atoms
We have experimentally investigated a spin excitation in a quantum degenerate
Fermi gas of atoms. In the hydrodynamic regime the damping time of the
collective excitation is used to probe the quantum behavior of the gas. At
temperatures below the Fermi temperature we measure up to a factor of 2
reduction in the excitation damping time. In addition we observe a strong
excitation energy dependence for this quantum statistical effect.Comment: 4 pages, 3 figure
Instability Heating of Sympathetically-Cooled Ions in a Linear Paul Trap
Sympathetic laser cooling of ions stored within a linear-geometry, radio
frequency, electric-quadrupole trap has been investigated using computational
and theoretical techniques. The simulation, which allows 5 sample ions to
interact with 35 laser-cooled atomic ions, revealed an instability heating
mechanism, which can prevent ions below a certain critical mass from being
sympathetically cooled. This critical mass can however be varied by changing
the trapping field parameters thus allowing ions with a very large range of
masses to be sympathetically cooled using a single ion species. A theoretical
explanation of this instability heating mechanism is presented which predicts
that the cooling-heating boundary in trapping parameter space is a line of
constant (ion trap stability coefficient), a result supported by the
computational results. The threshold value of depends on the masses of
the interacting ions. A functional form of this dependence is given
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