PhD

My PhD project focuses on the COSQUA projects, that stands for Cosmology and Quantum Simulations. I work in the Quantum Atom Optics under the supervision of Chris Westbrook and Denis Boiron. This project is in tight collaboration with two theoreticians : Scott Robertson, now researcher at Poitier, and Amaury Micheli, now post-doctoral fellow in Japan.

Introduction

In standard cosmological models, inflation is driven by a quantum field, the inflaton, whose constant energy density drives the superluminal expansion of the universe . When inflation stops, the universe has an extremely low density but the inflaton field starts to oscillate around its minimum of energy and decays into entangled pairs of particles . This is known as the pre-heating phase. Created pairs of particles then start to interact leading to decoherence and thermalization: the re-heating stage.

Although in situ observation of inflaton particle creation process is impossible, this pair production through parametric amplification is analogous to the creation of phonon pairs in a Bose-Einstein (BEC) condensate whose interaction strength is temporally modulated. Modulating the stiffness of a dipole trap of a cigar shaped BEC is equivalent to modulating the effective one-dimensional interaction strength in a BEC, and thus we are able to probe the correlation of entangled metastable helium atoms by the use of a micro-channel plate detector (MCP). Our experimental procedure is the following : we modulate in time the trap stiffness of the dipole trap laser and then release the trap (see figure 1). During expansion, the phonon kinetic energy is adiabatically transferred to one atom that is detected by the MCP after a 300 ms time of flight. The number of phonon pairs is expected to depend on the duration of the excitation, its amplitude, and the excitation frequency. However, the parameter range over which the entanglement of the phonon pairs can be observed is expected to be quite narrow . We propose to investigate the entanglement and correlations of those pairs of particles.

Experimental plateform

Results

We recently succeeded in observing a violation of the Cauchy-Schwarz inequality and squeezing (manuscript in preparation). Is this sufficient to assume non-separability of the state ? No : we need to make sure that their are no coherence between the modes and therefore to build an atomic interferometer

On the image here, a small slice of a Bose-Einstein condensate was extracted using a two photons transfer. Depending on the duration and shape of the pulse, it is possible to transfer an atom with probability 1 or 1/2, giving opportunity to do mirrors and beam-splitters. With this beams we should be able to probe the coherence between the two modes and therefore to demonstrate entanglement !