TY  - JOUR
A1  - Navez, Patrick
A1  - Wilkens, Martin
T1  - Single molecule in a Bose-Einstein condensate
N2  - We study a model describing a rotating linear rigid molicule interacting with a Bose-Einstein condensate. A generalization of the Landau criterion is established and gives the limit for which the molecule moves translationally and rotationally into the condensate without any friction. In particular, we show that the rotational energy released by the molecule is large enough to eject one atom out of the condensate. The detection of such an atom provides a direct measurement of the low-energy cross section of the scattering with the rotating molecule. Finally, increases of inertia and of centrifugal distortion of the molecule due to the surrounding condensate are estimated and compared with the experimental data obtained for a He4 droplet.
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Navez, Patrick
T1  - Macroscopic squeezing in Bose-Einstein condensate
N2  - We study the ground state of a uniform Bose gas at zero temperature in the Hartree-Fock-Bogoliubov (HFB) approximation. We find a solution of the HFB equations which obeys the Hugenholtz-Pines theorem. This solution imposes a macroscopic squeezing to the condensed state and as a consequence displays large particle number fluctuations. Particle number conservation is restored by building the appropriate U(1) invariant ground state via the superposition of the squeezed states. The condensed particle number distribution of this new ground state is calculated as well as its fluctuations which present a normal behavior.
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Illuminati, Fabrizio
A1  - Navez, Patrick
A1  - Wilkens, Martin
T1  - Thermodynamic identities and paricle number fluctuations in weakly interacting Bose-Einstein condensates
N2  - We derive exact thermodynamic identities relating the average number of condensed atoms and the root-mean- square fluctuations determined in different statistical ensembles for the weakly interacting Bose gas confined in a box. This is achieved by introducing the concept of auxiliary partition functions for model Hamiltonians that do conserve the total number of particles. Exploiting such thermodynamic identities, we provide the first, completely analytical prediction of the microcanonical particle number fluctuations in the weakly interacting Bose gas. Such fluctuations, as a function of the volume V of the box are found to behave normally, in contrast wiht the anomalous scaling behaviour V3/ 4 of the fluctuations in the ideal Bose gas.
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Idziaszek, Zbigniew
A1  - Gajda, M.
A1  - Navez, Patrick
A1  - Wilkens, Martin
A1  - Rzazewski, Kazimierz
T1  - Fluctuation of the Weakly Interacting Bose-Einstein Condensate
N2  - We consider the role of weak interaction on the fluctuations of the number of condensed atoms within canonical and microanonical ensembles. Unlike the correspinding case of the ideal gas this is not a clean, well-defined problem of mathematical physics. Two related reasons are the following: there is no unique way of defining the condensate fraction of the interacting system and no exact energy levels of the interacting system are known.
Y1  - 1999
ER  -