Research Interests:

Bose-Einstein condensates, spin squeezing

My projects cover two main aspects of the physics of atomic Bose-Einstein condenstates. The first aspect concerns fundamental properties, such as phase coherence, and finite temperature properties. The second aspect is on the use of Bose-Einstein condensates to create non-trivial states of the atomic field. In the future, such non classical states may play an important role in metrology (spin-squeezed states), for probing the frontiers between quantum and classical world (Schrodinger cats) and for quantum information.

We developed 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 extention of the classical concept of ergodicity in the system. With Hadrien Kurkjian and Yvan Castin we are presently studying phase coherence in fermionic pair-condensed systems (see the note on the LKB website).
About spin squeezing in BEC, I investigate the role of decoherence, due to finite temperature and particle losses. I collaborate with the experimentalists of the Atom chip group of Jakob Reichel in Paris http://www.lkb.ens.fr/-Atom-Chips and of with the group Philipp Treutlein http://atom.physik.unibas.ch/people/philipptreutlein.php. In particular I participated to one of the two first realizations of spin squeezed states in a bimodal condensate (see note on the LKB website).

Quantum optics

In the past I worked with Philippe Grangier and his group on Quantum Non Demolition Measurements using cold atoms in an optical cavity, and on the generation of squeezed light with Luigi Lugiato in Milan. More recently, with GaŽl Reinaudi, Frank LaloŽ and the quantum optics group of Michel Pinard and Elisabeth Giacobino, we made a theoretical proposal for a long-lived quantum memory using nuclear spins of He3. Spin-polarization of Helium-3 by optical pumping and metastability exchange collisions has been used since many years in our Laboratory, and we could show that the same technique could be used to transfer quantum correlations of the light to the spins (and back).

Optical pumping of helium-3 for medical application

Polarized helium-3 can be used for imaging human lungs by nuclear magnetic resonance. http://www.lkb.ens.fr/recherche/flquant/index.html.
The gas is usually polarized by metastability exchange optical pumping at low pressure and then compressed to atmospheric pressure to be inhaled. With Marie Abboud, Pierre-Jean Nacher, GeneviŤve Tastevin and Xavier Maitre, we demonstrated a new optical pumping scheme at high magnetic field allowing to prepare highly polarized samples of He3 directly at relatively high pressure (up to almost 100 times the usual pressure for metastability exchange optical pumping).

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