Institut des
NanoSciences de Paris
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Thesis Defense - Romain Anankine - Friday 16 june 2017 at 2 pm

Romain Annakine, PhD Student - Team Nanostructures and quantum systems

Quantum coherence and superfluidity of a trapped excitons gas

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Abstract

Semiconductor excitons are bosonic quasi-particles compound of an electron and a hole bound by Coulomb attraction. They can undergo Bose-Einstein condensation in a very original fashion : excitons are distributed among four « spin » states. The lowest energy states are « dark » because optically inactive while at a higher energy, two « bright » states are coupled to the photon field. Below sub-kelvin temperatures, condensation of excitons leads to a macroscopic population of the dark states, as demonstrated in M. Beian’s thesis in 2015. This dark condensate is coherently coupled with a small fraction of bright excitons whose their weak photoluminescence emitted allows to probe signatures for quantum coherence. In this thesis, we show the contribution of bright excitons to the Bose-Einstein condensation. We study a 2D dilute gas of excitons confined in a electrostatic trap where we reveal, below a critical temperature of about 1 K, a quantum long-range order with an increased temporal coherence of the photoluminescence emitted by bright excitons. The appearance of quantised vortices, signalled by density defects and phase singularities in spatial interferences patterns, gives us the demonstration that 85% of the trapped excitons participate in the formation of a four-component superfluid where a macroscopic population of dark excitons is coherently coupled with a fraction of condensed bright excitons.

Jury

Emmanuelle Deleporte, protractor
Masha Vladimirova, protractor
Markus Holzmann, examinator
Alice Sinatra, examinator
François Dubin, thesis director