Biomedical subjects

J N Fuchs

Publications and source records attributed to J N Fuchs.

3 recordsLinked to original sources

PubMed2005

Spin waves in a one-dimensional spinor bose gas.

We study a one-dimensional (iso)spin 1/2 Bose gas with repulsive delta-function interaction by the Bethe Ansatz method and discuss the excitations above the polarized ground state. In addition to phonons the system features spin waves with a quadratic dispersion. We compute analytically and numerically the effective mass of the spin wave and show that the spin transport is greatly suppressed in the strong coupling regime, where the isospin-density (or "spin charge") separation is maximal. Using a hydrodynamic approach, we study spin excitations in a harmonically trapped system and discuss prospects for future studies of two-component ultracold atomic gases.

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PubMed2004

Exactly solvable model of the BCS-BEC crossover.

We discuss an integrable model of interacting fermions in one dimension that allows a complete description of the crossover from a BCS- to a Bose-like superfluid. This model bridges the Gaudin-Yang model of attractive spin 1/2 fermions to the Lieb-Liniger model of repulsive bosons. Using a geometric resonance in the one-dimensional scattering length, the inverse coupling constant varies from -infinity to +infinity while the system evolves from a BCS-like state through a Tonks-Girardeau gas to a weakly interacting Bose gas of dimers. We study the ground state energy, the elementary density and spin excitations, and the correlation functions. An experimental realization with cold atoms of such a one-dimensional BCS-BEC crossover is proposed.

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PubMed2002

Internal state conversion in ultracold gases.

We consider an ultracold gas of (noncondensed) bosons or fermions with two internal states, and we study the effect of a gradient of the transition frequency between these states. When a pi/2 rf pulse is applied to the sample, exchange effects during collisions transfer the atoms into internal states which depend on the direction of their velocity. This results, after a short time, in a spatial separation between the two states. A kinetic equation is solved analytically and numerically; the results agree well with the recent observations of Lewandowski et al.

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