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1.
Phys Rev Lett ; 122(9): 093403, 2019 Mar 08.
Artículo en Inglés | MEDLINE | ID: mdl-30932523

RESUMEN

We demonstrate the existence of a collective excitation branch in the pair-breaking continuum of superfluid Fermi gases and BCS superconductors. At zero temperature, we analytically continue the equation on the collective mode energy in Anderson's Random Phase Approximation or Gaussian fluctuations through its branch cut associated with the continuum, and obtain the full complex dispersion relation, including in the strong coupling regime. The branch exists as long as the chemical potential µ is positive and the wave number below sqrt[2mµ]/ℏ (with m the fermion mass). In the long wavelength limit, the branch varies quadratically with the wave number, with a complex effective mass that we compute analytically for an arbitrary interaction strength.

2.
Phys Rev Lett ; 107(6): 060404, 2011 Aug 05.
Artículo en Inglés | MEDLINE | ID: mdl-21902302

RESUMEN

We show that, at finite temperature, the maximum spin squeezing achievable using interactions in Bose-Einstein condensates has a finite limit when the atom number N→∞ at fixed density and interaction strength. We calculate the limit of the squeezing parameter for a spatially homogeneous system and show that it is bounded from above by the initial noncondensed fraction.

3.
Phys Rev Lett ; 77(27): 5315-5319, 1996 Dec 30.
Artículo en Inglés | MEDLINE | ID: mdl-10062773
4.
Phys Rev Lett ; 74(19): 3772-3775, 1995 May 08.
Artículo en Inglés | MEDLINE | ID: mdl-10058293
5.
Phys Rev Lett ; 68(5): 580-583, 1992 Feb 03.
Artículo en Inglés | MEDLINE | ID: mdl-10045937
6.
Phys Rev Lett ; 76(24): 4508-4511, 1996 Jun 10.
Artículo en Inglés | MEDLINE | ID: mdl-10061309
7.
Phys Rev Lett ; 100(21): 210401, 2008 May 30.
Artículo en Inglés | MEDLINE | ID: mdl-18518586

RESUMEN

The problem of spin squeezing with a bimodal condensate in the presence of particle losses is solved analytically by the Monte Carlo wave function method. We find the largest obtainable spin squeezing as a function of the one-body loss rate, the two-body and three-body rate constants, and the s-wave scattering length.

8.
Phys Rev Lett ; 87(19): 190402, 2001 Nov 05.
Artículo en Inglés | MEDLINE | ID: mdl-11690401

RESUMEN

We consider a Bose-Einstein condensate subject to a rotating harmonic potential, in connection with recent experiments leading to the formation of vortices. We use the classical hydrodynamic approximation to the nonlinear Schrödinger equation to determine almost analytically the evolution of the condensate. We predict that this evolution can exhibit dynamical instabilities, for the stirring procedure previously demonstrated at ENS and for a new stirring procedure that we put forward. These instabilities take place within the range of stirring frequency and amplitude for which vortices are produced experimentally. They provide therefore an initiating mechanism for vortex nucleation.

9.
Phys Rev Lett ; 87(21): 210404, 2001 Nov 19.
Artículo en Inglés | MEDLINE | ID: mdl-11736326

RESUMEN

We propose a method to study the time evolution of Bose-Einstein condensed gases perturbed from an initial thermal equilibrium, based on the Wigner representation of the N-body density operator. We show how to generate a collection of random classical fields sampling the initial Wigner distribution in the number conserving Bogoliubov approximation. The fields are then evolved with the time dependent Gross-Pitaevskii equation. We illustrate the method with the damping of a collective excitation of a one-dimensional Bose gas.

10.
Phys Rev Lett ; 92(15): 150404, 2004 Apr 16.
Artículo en Inglés | MEDLINE | ID: mdl-15169272

RESUMEN

We consider a gas of cold fermionic atoms having two spin components with interactions characterized by their s-wave scattering length a. At positive scattering length the atoms form weakly bound bosonic molecules which can be evaporatively cooled to undergo Bose-Einstein condensation, whereas at negative scattering length BCS pairing can take place. It is shown that, by adiabatically tuning the scattering length a from positive to negative values, one may transform the molecular Bose-Einstein condensate into a highly degenerate atomic Fermi gas, with the ratio of temperature to Fermi temperature T/T(F) approximately 10(-2). The corresponding critical final value of k(F)/a/, which leads to the BCS transition, is found to be about one-half, where k(F) is the Fermi momentum.

11.
Phys Rev Lett ; 88(25 Pt 1): 250403, 2002 Jun 24.
Artículo en Inglés | MEDLINE | ID: mdl-12097078

RESUMEN

We study experimentally and theoretically a cold trapped Bose gas under critical rotation, i.e., with a rotation frequency close to the frequency of the radial confinement. We identify two regimes: the regime of explosion where the cloud expands to infinity in one direction, and the regime where the condensate spirals out of the trap as a rigid body. The former is realized for a dilute cloud, and the latter for a condensate with the interparticle interaction exceeding a critical value. This constitutes a novel system in which repulsive interactions help in maintaining particles together.

12.
Science ; 296(5571): 1290-3, 2002 May 17.
Artículo en Inglés | MEDLINE | ID: mdl-12016308

RESUMEN

We report the production of matter-wave solitons in an ultracold lithium-7 gas. The effective interaction between atoms in a Bose-Einstein condensate is tuned with a Feshbach resonance from repulsive to attractive before release in a one-dimensional optical waveguide. Propagation of the soliton without dispersion over a macroscopic distance of 1.1 millimeter is observed. A simple theoretical model explains the stability region of the soliton. These matter-wave solitons open possibilities for future applications in coherent atom optics, atom interferometry, and atom transport.

13.
Phys Rev A ; 54(6): 5275-5290, 1996 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-9914095
14.
Phys Rev A ; 51(5): R3426-R3428, 1995 May.
Artículo en Inglés | MEDLINE | ID: mdl-9912120
15.
Phys Rev A ; 51(5): 3896-3901, 1995 May.
Artículo en Inglés | MEDLINE | ID: mdl-9912061
16.
Phys Rev A ; 50(6): 5092-5115, 1994 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-9911512
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