451 research outputs found
Condensed matter physics with trapped atomic Fermi gases
We present an overview of the various phase transitions that we anticipate to
occur in trapped fermionic alkali gases. We also discuss the prospects of
observing these transitions in (doubly) spin-polarized Li-6 and K-40 gases,
which are now actively being studied by various experimental groups around the
world.Comment: 18 pages of LaTeX and 2 postscript figures. Contribution to the
international summer school `Enrico Fermi' on Bose-Einstein condensation in
atomic gases, Varenna 199
Theory of Interacting Quantum Gases
We present a unified picture of the interaction effects in dilute atomic
quantum gases. We consider fermionic as well as bosonic gases and, in
particular, discuss for both forms of statistics the fundamental differences
between a gas with effectively repulsive and a gas with effectively attractive
interatomic interactions, i.e.\ between a gas with either a positive or a
negative scattering length.Comment: Invited paper for the NIST Journal of Researc
Critical Temperature of a Trapped Bose Gas: Mean-Field Theory and Fluctuations
We investigate the possibilities of distinguishing the mean-field and
fluctuation effects on the critical temperature of a trapped Bose gas with
repulsive interatomic interactions. Since in a direct measurement of the
critical temperature as a function of the number of trapped atoms these effects
are small compared to the ideal gas results, we propose to observe
Bose-Einstein condensation by adiabatically ramping down the trapping
frequency. Moreover, analyzing this adiabatic cooling scheme, we show that
fluctuation effects can lead to the formation of a Bose condensate at
frequencies which are much larger than those predicted by the mean-field
theory.Comment: 4 pages of ReVTeX and 3 figures. Submitted to Physical Review
Influence of infection on the distribution patterns of NIH-Chronic Prostatitis Symptom Index scores in patients with chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS)
Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) is a complex condition for which the etiological determinants are still poorly defined. To better characterize the diagnostic and therapeutic profile of patients, an algorithm known as UPOINT was created, addressing six major phenotypic domains of CP/CPPS, specifically the urinary (U), psycho-social (P), organ-specific (O), infection (I), neurological/systemic (N) and muscular tenderness (T) domains. An additional sexual dysfunction domain may be included in the UPOINT(S) system. The impact of the infection domain on the severity of CP/CPPS symptoms is a controversial issue, due to the contradictory results of different trials. The aim of the present retrospective study was to further analyze the extent to which a positive infection domain of UPOINTS may modify the pattern of CP/CPPS symptom scores, assessed with the National Institutes of Health-Chronic Prostatitis Symptom Index (NIH-CPSI). In a cohort of 935 patients that was divided on the basis of the presence or absence of prostatic infection, more severe clinical symptoms were shown by the patients with infection (median NIH total score: 24 versus 20 points in uninfected patients; P<0.001). Moreover, NIH-CPSI score distribution curves were shifted towards more severe symptoms in patients with a positive infection domain. Division of the patients into the six most prominent phenotypic clusters of UPOINTS revealed that the 'prostate infection-related sexual dysfunction' cluster, including the highest proportion of patients with evidence of infection (80%), scored the highest number of NIH-CPSI points among all the clusters. To assess the influence of the infection domain on the severity of patients' symptoms, all subjects with evidence of infection were withdrawn from the 'prostate infection-related sexual dysfunction' cluster. This modified cluster showed symptom scores significantly less severe than the original cluster, and the CPSI values became comparable to the scores of the five other clusters, which were virtually devoid of patients with evidence of infection. These results suggest that the presence of pathogens in the prostate gland may significantly affect the clinical presentation of patients affected by CP/CPPS, and that the infection domain may be a determinant of the severity of CP/CPPS symptoms in clusters of patients phenotyped with the UPOINTS system. This evidence may convey considerable therapeutic implications
Cooper pair formation in trapped atomic Fermi gases
We apply the closed time-path formalism to evaluate the dynamics of the BCS
transition to the superfluid state in trapped atomic Li. We find that the
Fokker-Planck equation for the probability distribution of the order parameter
is, sufficiently close to the critical temperature, identical to the equation
that describes the switching on of a single-mode laser.Comment: 4 pages revtex including 1 figur
The Superfluid State of Atomic Li6 in a Magnetic Trap
We report on a study of the superfluid state of spin-polarized atomic Li6
confined in a magnetic trap. Density profiles of this degenerate Fermi gas, and
the spatial distribution of the BCS order parameter are calculated in the local
density approximation. The critical temperature is determined as a function of
the number of particles in the trap. Furthermore we consider the mechanical
stability of an interacting two-component Fermi gas, both in the case of
attractive and repulsive interatomic interactions. For spin-polarized Li6 we
also calculate the decay rate of the gas, and show that within the mechanically
stable regime of phase space, the lifetime is long enough to perform
experiments on the gas below and above the critical temperature if a bias
magnetic field of about 5 T is applied. Moreover, we propose that a measurement
of the decay rate of the system might signal the presence of the superfluid
state.Comment: 16 pages Revtex including 10 figures, submitted to Phys. Rev.
Magnetic field control of elastic scattering in a cold gas of fermionic lithium atoms
We study elastic collisions in an optically trapped spin mixture of fermionic
lithium atoms in the presence of magnetic fields up to 1.5kG by measuring
evaporative loss. Our experiments confirm the expected magnetic tunability of
the scattering length by showing the main features of elastic scattering
according to recent calculations. We measure the zero crossing of the
scattering length that is associated with a predicted Feshbach resonance at
530(3)G. Beyond the resonance we observe the expected large cross section in
the triplet scattering regime
Equivalent Linear Two-Body Equations for Many-Body Systems
A method has been developed for obtaining equivalent linear two-body
equations (ELTBE) for the system of many () bosons using the variational
principle. The method has been applied to the one-dimensional N-body problem
with pair-wise contact interactions (McGurie-Yang N-body problem) and to the
dilute Bose-Einstein condensation (BEC) of atoms in anisotropic harmonic traps
at zero temperature. For both cases, it is shown that the method gives
excellent results for large N.Comment: 12 pages, Late
Critical temperature and Ginzburg-Landau equation for a trapped Fermi gas
We discuss a superfluid phase transition in a trapped neutral-atom Fermi gas.
We consider the case where the critical temperature greatly exceeds the spacing
between the trap levels and derive the corresponding Ginzburg-Landau equation.
The latter turns out to be analogous to the equation for the condensate wave
function in a trapped Bose gas. The analysis of its solution provides us with
the value of the critical temperature and with the spatial and
temperature dependence of the order parameter in the vicinity of the phase
transition point.Comment: 6 pages, 1 figure, REVTeX. The figure improved. Misprints corrected.
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