Finite temperature decoherence in Bose-Einstein condensates

Keith R. Burnett

Thorsten Schumm, Sebastian Hofferberth, Jörg Schmiedmayer

We perform interferometry with one-dimensional Bose-Einstein condensates in a double well potential. Using dressed adiabatic potentials on an atomchip, we dynamically split BECs, imposing a macroscopic coherence on the system. Fluctuations of the order parameter are revealed as local shifts in the interference pattern and allow a quantization of the decoherence process with time. For the uncoupled system we ultimately recover individual phase fluctuating condensates, whereas finite tunnel coupling counteracts the decoherence and leads to an equilibrium characterized by a finite coherence length. Decoherence decay and equilibrium coherence lengths are used to determine temperature and coupling strength of the system.

Wolfgang Ketterle

H. T. Ng, Sougato Bose

We study a two-level atom coupled to a Bose-Einstein condensate. We show that the rules governing the decoherence of mesoscopic superpositions involving different classical-like states of the condensate can be probed using this system. This scheme is applicable irrespective of whether the condensate is initially in a coherent, thermal, or more generally, in any mixture of coherent states. The effects of atom loss and finite temperature to the decoherence can therefore be studied. We also discuss the various noise sources causing the decoherence.

David A. W. Hutchinson

Robert Graham

The phase diffusion of the order parameter of trapped Bose-Einstein condensates at temperature ${k}_{B}T\ensuremath{\gg}\ensuremath{\Elzxh}\overline{\ensuremath{\omega}}$ is determined, which gives the fundamental limit of the linewidth $\ensuremath{\Delta}\ensuremath{\nu}$ of an atom laser. In addition a prediction of the number fluctuations in the condensate and their correlation time ${\ensuremath{\tau}}_{c}$ is made and a general relation for $\ensuremath{\Delta}\ensuremath{\nu}{\ensuremath{\tau}}_{c}$ is derived from the fluctuation-dissipation relation.