HAL will be down for maintenance from Friday, June 10 at 4pm through Monday, June 13 at 9am. More information
Skip to Main content Skip to Navigation
Theses

Theoretical and experimental study of spin-1 antiferromagnetic Bose-Einstein Condensates

Abstract : In this thesis, we study theoretically and in experimentally the properties of spin-1 Bose-Einstein condensates with antiferromagnetic interactions realized in the ultra-cold sodium gases confined in optical dipole traps. We present in detail how to realize, diagnose and control the spinor Bose-Einstein condensates in our experiment. In order to describe the condensate, a mean-field theory is first adopted. This theory predicts a phase transition when changing the magnetic field $B$. The predictions of the mean-field theory agree very well with most of our experimental results, including the values of the critical magnetic field $B_c$, asymptotic values of $n_0$ (relative atom number in $m_F=0$ state) at large $B$ and the phase diagram of $n_0$. However, for small magnetization and small magnetic fields, we find abnormally large fluctuations (super-Poissonian) of $n_0$. In order to describe these large fluctuations, we develop a full quantum statistical description for the spinor condensate at finite temperature. To describe uncondensed thermal atoms (also present in the same trap), we use the ``semi-ideal" Hartree-Fock approximation to deal with the interactions between the condensate atoms and the thermal ones. The experimental results lead us to introduce two kinds of temperatures, the ``spin temperature" $T_s$ and the ``kinetic temperature" $T_k$ with $T_s\ll T_k$, characterizing respectively the fluctuaitons of the condensate spin and the thermal gas. We conclude that the system is reaching a quasi-equilibrium states, where different degrees of freedom reach equilibrium by separate mechanisms but where the mutual thermalization does not occur over the lifetime of the cloud.
Complete list of metadata

Cited literature [137 references]  Display  Hide  Download

https://tel.archives-ouvertes.fr/tel-01104387
Contributor : Fabrice Gerbier Connect in order to contact the contributor
Submitted on : Friday, January 16, 2015 - 4:05:36 PM
Last modification on : Thursday, March 17, 2022 - 10:08:07 AM
Long-term archiving on: : Friday, September 11, 2015 - 6:59:14 AM

Identifiers

  • HAL Id : tel-01104387, version 1

Citation

Lingxuan Shao. Theoretical and experimental study of spin-1 antiferromagnetic Bose-Einstein Condensates. Quantum Gases [cond-mat.quant-gas]. Ecole Normale Supérieure, 2014. English. ⟨tel-01104387⟩

Share

Metrics

Record views

324

Files downloads

443