## Bose-Einstein condensates, degenerate Fermi gases, spin squeezing

- Phase Coherence of a BEC at finite Temperature
- BEC Spin Squeezing and SchrÃ¶dinger cats in presence of particle losses
- Experimental realization of Spin Squeezing with a Bose-Einstein condensate
- Limit of Spin Squeezing in finite temperature condensates
- Phase operators and blurring time of a pair-condensed Fermi gas
- Phase Coherence time of a pair-condensed Fermi gas at finite temperature
- Entangled states of an atomic ensemble in a resonant cavity

Our projects cover two main aspects of the physics of cold gases and atomic Bose-Einstein condensates. The first one concerns fundamental properties, such as phase coherence, correlations, and multimode finite temperature aspects. The second one is on the use of Bose-Einstein condensates and cold gases to create non-classical states of the atomic field that may be useful in metrology (spin-squeezed states), in probing the frontiers between the quantum and the classical world (SchrÃ¶dinger cats) and for quantum information.

We developed analytical and theoretical tools including **classical field methods** to describe a degenerate Bose gas including thermal and possibly quantum fluctuations. We then applied these methods to different problems as for example the **nucleation and crystallization of a vortex** lattice in a rotating Bose-Einstein condensate, or the **spreading in time of the condensate phase at finite temperature**. With Emilia Witkowska and Yvan Castin, we could show that the condensate phase spreads ballistically in time at finite temperature and we calculated the coefficient of phase spreading using a quantum extension of the classical concept of ergodicity in the system. With Hadrien Kurkjian and Yvan Castin we study** phase coherence in fermionic pair-condensed systems**.

Concerning **spin squeezing in BEC**, we investigate the role of **decoherence, due to finite temperature and particle losses**. We collaborate with the experimentalists of the Atom chip group of Jakob Reichel in LKB and with the group of Philipp Treutlein in Basel Unversity. In particular we participated to one of the two first realizations of spin squeezed states in a bimodal condensate.

For further information, please visit the personal website of Alice Sinatra:

http://www.phys.ens.fr/~sinatra/