Fermionic Cloud Research Articles

Shrinking of a condensed fermionic cloud in a trap approaching the Bose-Einstein condensation limit

We determine the zero-temperature density profile of a cloud of fermionic atoms in a trap subject to a mutual attractive interaction, as the strength of the interaction is progressively increased. We find a significant decrease of the size of the atomic cloud as it evolves from the weak-coupling (BCS) regime of overlapping Cooper pairs to the strong-coupling (Bose-Einstein) regime of non-overlapping bound-fermion pairs. Most significantly, we find a pronounced increase of the value of the density at the center of the trap (even by an order of magnitude) when evolving between the two regimes. Our results are based on a generalized Thomas-Fermi approximation for the superfluid state, that covers continuously all coupling regimes.

Collective dynamics of fermion clouds in cigar-shaped traps

The propagation of zero sound in a spin-polarized Fermi gas under harmonic confinement is studied as a function of the mean-field interactions with a second Fermi gas. A local-density treatment is compared with the numerical solution of the Vlasov–Landau equations for the propagation of density distortions in a trapped two-component Fermi gas at temperature T=0.2 T F . The response of the gas to the sudden creation of a sharp hole at its centre is also studied numerically.

Temperature dependence of density profiles for a cloud of noninteracting fermions moving inside a harmonic trap in one dimension

We extend to finite temperature a Green's-function method that was previously proposed to evaluate ground-state properties of mesoscopic clouds of noninteracting fermions moving under harmonic confinement in one dimension. By calculations of the particle and kinetic-energy density profiles, we illustrate the role of thermal excitations in smoothing out the quantum shell structure of the cloud and in spreading the particle spill out from quantum tunnel at the edges. We also discuss the approach of the exact density profiles to the predictions of a semiclassical model often used in the theory of confined atomic gases at finite temperature.

Explicit Finite-Difference and Particle Method for the Dynamics of Mixed Bose-Condensate and Cold-Atom Clouds

We present a new numerical method for studying the dynamics of quantum fluids composed of a Bose–Einstein condensate and a cloud of bosonic or fermionic atoms in a mean-field approximation. The method combines an explicit time-marching algorithm, previously developed for Bose–Einstein condensates in a harmonic or optical-lattice potential, with a particle-in-cell approach to the equation of motion for the one-body Wigner distribution function in the cold-atom cloud. The method is tested against known analytical results on the free expansion of a fermion cloud from a cylindrical harmonic trap and is validated by examining how the expansion of the fermionic cloud is affected by the simultaneous expansion of a condensate. We then present original calculations on a condensate and a thermal cloud inside a harmonic well and a superposed optical lattice, by addressing the free expansion of the two components and their oscillations under an applied harmonic force. These results are discussed in the light of relevant theories and experiments.

Structure and stability of trapped atomic boson-fermion mixtures

The structure of trapped binary mixtures of bosonic and fermionic atoms at zero temperature is studied using a modified Gross-Pitaevskii equation for the bosons which self-consistently includes the mean-field interaction generated by the fermionic cloud. The density of the fermionic component is described within the Thomas-Fermi approximation. The influence of the boson-boson and the boson-fermion s-wave interaction on the density profiles and the stability of the mixture is investigated systematically. Critical particle numbers for the mean-field collapse caused either by attractive boson-boson or by attractive boson-fermion interactions and for the onset of spatial component separation are discussed. It is shown that the interplay between the boson-boson and the boson-fermion interaction generates a rich and complex phase diagram. Finally, the specific properties and prospects of the boson-fermion mixtures available in present experiments are addressed.

Scaling theory of dynamic scattering centers and moving heavy particles in a fermionic environment.

A dynamic scattering object and the slowly building screening fermion cloud around it are examined. The models previously studied for strong on-site scattering---x-ray absorption, the anisotropic Kondo problem, the Anderson model, etc.---have the common feature that all values of the bare scattering matrix commute with one another. Nozi\`eres and De Dominicis's path-integral method can be applied directly to these problems because the scatterings in different channels are independent. The aim of this paper is to extend the theory to those problems, in which the scattering matrix has noncommuting values as, e.g., in the case of a scattering center moving in real space. Integrating over the fermionic degrees of freedom, we get to the problem of a one-dimensional dielectric medium with moving domain walls. In contrast to the commutative case, more-than-two-particle interactions may arise between the domain walls. Renormalization is carried out by keeping the terms that are the most divergent in the short-time-cutoff parameter.

Electric properties of fermion cloud around a monopole

We analyze the electric properties of the fermion cloud around a monopole and show that the external source with an integer charge put into the fermion cloud is completely screened. Therefore, the integer charge of the dyon, which is supplied by heavy bosons, is screened. We also study the induced charge of the fermion cloud due to the effect of the external source with a fractional charge and find that the induced charge locally screens the external charge and that the same amount of the fractional charge as the external one is induced outside of the external source. We also discuss a similar screening phenomenon of the dyon in the standardSU (5) model.