30 Novembre – Thesis defense - Maxime Bellouvet

13 h30 Amphi IOA - LP2N Institut d’Optique d’Aquitaine (Talence)

Bose-Einstein condensation and simulation of a method to trap ultracold atoms in subwavelength potentials in the near-field of a nanostructured surface.

An interest for hybrid quantum systems (HSQs) has been growing up for the last decades. This object combines two quantum systems in order to take advantage of both systems' qualities, not available with only one. Among these quantum systems, ultracold atoms distinguish themselves by their strong decoupling from environment which enables an excellent control of their intrinsic properties. Optical lattice quantum simulators with tunable properties (energy scale, geometry,...) allows one to investigate new regimes in condensed matter physics. In this quest for exotic quantum phases (e.g., antiferromagnetism), the reduction of thermal entropy is a crucial challenge. The price to pay for such low temperature and entropy is a long thermalization time that will ultimately limit the experimental realization. Miniaturization of lattice spacing is a promising solution to speed up the dynamics. Engineering cold atom hybrids offers promising perspectives but requires us to interface quantum systems in different states of matter at very short distances, which still remains an experimental challenge.
This thesis is part of the AUFRONS project, which aims at cooling down an atomic gas until the quantum degeneracy regime then transport and trap this cloud in the near field of a nanostructure. The idea is to trap cold atoms in a two-dimensional subwavelength lattice, at a few tenth of nm away from the surface. One goal is to study atom-atom interactions within the lattice but also atom-surface modes coupling.
The work realized during this thesis splits into an experimental part and a theoretical part. In the first one, we present the cooling of 87Rb atoms until the quantum degeneracy regime. The second part is dedicated to theoretical simulations of a new trapping method we have implemented to trap and manipulate cold atoms below 100 nm from structures. This method takes advantage of plasmonic resonance and vacuum forces (Casimir-Polder effect). It allows one to create subwavelength potentials with controllable parameters. We detail the calculations of optical and vacuum forces to apply them to an atom of 87Rb in the vicinity of a 1D nanostructure.

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