I did my phD studies in Alain Aspect's atom optic group.
I worked on Bose-Einstein condensation (BEC) and it's application to quantum-intereferomotric sensing of inertial fields.
In spring 2004 Rob Nyman and I have started building a new experiment (nicknamed "KRub") to produce a new BEC source for the study of degenerate atomic gases in atom-interferometry. In falls 2005 we were joined by Jean-François Clément and in june 2006 by Jean-Philippe Brantut.
The experiment is now leading a life of its own, as I defended my phD in January 2008.
- We often took pictures of the work in progress in the lab, and you see them on KRubLog, the unofficial blog of the experiment.
KRubLog: pictures of the "KRub" experiment.
In September 2006 I started the "little-ICE" project, a spin-off of our main experiment to perform atom-interferometric measurements in ballistic flights: 20 seconds of micro-gravity in a free-falling plane.
In particular, we demonstrated the first atom interferometer to perform in microgravity.
An interferometric device compares the phase-shift undergone by test particles in two different paths (that can by spatially separated, or only separated by internal parameters). It can thus read to a high precision the potential felt by the test particles.
Photon-interferometry is a well established technique for high precision measurements. State of the art gravimeters are made of a falling test mass whose acceleration is read by photon interferometry. Sagnac-effect gyrometers drive inertial-navigation centers of almost all planes.
Atom-interferometry promises orders of magnitude more sensitivity than photon-interferometry but is still in its infancy.
Long term goals of our research project (see also our group's webpage ):
The use of ultracold atomic gases as a source for matter-wave interferometry allows high signal-to-noise ratio due to high densities and narrow momentum-spectra. To avoid inhomogeneities of external potential, propagation between beam splitters in an atom interferometer is usually achieved via free-fall. The sensitivity of an interferometric measurement is limited in current high-precision experiments by the propagation time of the atoms, itself limited by the free expansion of the atomic cloud in the vacuum chamber. The use of a Bose-condensed cloud dramaticaly reduces the ballistic expansion and allows for long propagation times.
To access experimentally such long fall times we are building a transportable atom-interferometry apparatus that can be used on an aeroplane, in ballistic flights, to perform measurements in micro-gravity. A mixture of quantum degenerate gases, bosonic 87Rb and fermionic 40K, will be used in a Raman-pulse interferometer for accelerometry.
Interactions in high density samples such as Bose-condensed gases give rise to systematic shifts in interferometric measurements. Fermionic degenerate gases have a broad momentum distribution but negligible collisions. We plan to study the importance of interaction shifts in our 87 Rb bosonic sample using a Fermi gas of 40K.
 R. A. Nyman, G. Varoquaux, B. Villier, D. Sacchet, F. Moron, Y. Le Coq, A. Aspect, and P. Bouyer, Tapered-amplified AR-coated laser diodes for Potassium and Rubidium atomic-physics experiments , Review of Scientific Instruments 77, 033105 (2006)
 R. A. Nyman, G. Varoquaux, F. Lienhart, D. Chambon, S. Boussen, J.-F. Clément, T. Muller, G. Santarelli, F. Pereira Dos Santos, A. Clairon, A. Bresson, A. L., Philippe Bouyer, I.C.E.: a Transportable Atomic Inertial Sensor for Test in Microgravity , Journal of Applied physics B, 84 673-681 (2006)
 G. Varoquaux, N. Zahzam, W. Chaibi, J.-F. Clément, O. Carraz, J.-P. Brantut, R. A. Nyman, F. Pereira Dos Santos, L. Mondin, M. Rouzé, Y. Bidel, A. Bresson, A. Landragin, P. Bouyer, I.C.E.: An Ultra-Cold Atom Source for Long-Baseline Interferometric Inertial Sensors in Reduced Gravity , Proceedings of the "Rencontres de Moriond, Gravitational Waves and Experimental Gravity", March 2007
 E. Varoquaux and G. Varoquaux, The Sagnac effect in superfluids. Uspekhi Fizicheskikh Nauk 2, 217 (Feb. 2008).
 G. Varoquaux, Agile computer control of a complex experiment. Computing in Science and Engineering 10(2), 55 (2008).
 P. Bouyer, G. Varoquaux, R. A. Nyman, J.-P. Brantut, G. Stern, T. Bourdel, B. Battelier, A. Landragin, O. Chaibi, F. Pereira Dos Santos, A. Bresson, N. Zahzam, Y. Bidel, O. Carras, M. Rouzé, and L. Mondin Testing the universality of free fall in a freely-falling two-species atom interferometer: the I.C.E project, Proceedings of the International Conference on Space Optics, Toulouse, France, October 2008.
 J.P. Brantut, J.F. Clement, M.R. de Saint Vincent, G. Varoquaux, R.A. Nyman, A. Aspect, T. Bourdel, P. Bouyer, Light-shift tomography in an optical-dipole trap for neutral atoms, Physical Review A., 78, (3), pp. 31401, (2008).
 G. Stern , B. Battelier, R. Geiger, G. Varoquaux, A. Villing, F. Moron, O. Carraz, N. Zahzam, Y. Bidel, W. Chaibi, F. Pereira Dos Santos, A. Bresson, A. Landragin, and P. Bouyer Light-pulse atom interferometry in microgravity, European Physical Journal D, 53, 353-357, (2009).
 G. Varoquaux, R.A. Nyman, R. Geiger, P. Cheinet, A. Landragin and P. Bouyer, How to estimate the differential acceleration in a two-species atom interferometer to test the equivalence principle, New Journal of Physics, 11 113010, (2009).