Research Interests:
Bose-Einstein condensates, spin squeezing
My projects cover two main aspects of the physics of atomic
Bose-Einstein condensates. 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 (Schrödinger 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).
Summary of results for spin squeezing and Schrodinger cats in BEC (multimode treatment and losses)
Resume_Squeezing_Chats.pdf
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.
With Gaël Reinaudi, Frank Laloë 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). More recently, with Alan Serafin, Yvan Castin, Matteo Fadel and Philipp Treutlein, we have
studied the possibility to obtain nuclear spin squeezing in a cell of helium-3 atoms at room temperature by quantum non-demolition measurements.
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, Geneviève
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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