Thesis defense of Victor GONDRET

Thesis defense of Victor GONDRET, PhD student in the Quantum gases group of the Laboratoire Charles Fabry, on Tuesday 28 January 2025 at 02:00pm in the Auditorium of the Institut d'Optique Graduate School in Palaiseau, on the topic: "on the entanglement of quasi-particles in a Bose-Einstein condensate."

Abstract: "Parametric resonance is a recurrent phenomenon in physics, observable at all scales. For example, the vibration of a mirror in a cavity leads to the production of photons, a phenomenon known as the dynamical Casimir effect. In 1831, Faraday observed that a container of water excited vertically in a sinusoidal manner generates patterns with a frequency that is half of the excitation frequency. In the primordial universe, after inflation, parametric oscillations of a field (the inflaton) led to the creation of particles, whose thermalization subsequently gave rise to the hot, dense state often associated with the Big Bang.

The growth in the number of quasi-particles (or particles) in the excited mode(s) is triggered by the system’s thermal fluctuations. When the system is initially empty, at zero temperature, quantum fluctuations initiate this growth. This work experimentally studies the dynamics of quasi-particle creation out of vacuum in a Bose-Einstein condensate subject to parametric excitation.

After introducing the context of this work, we will discuss the dynamics of quasi-particle creation. In the second part, we will highlight the role of quantum fluctuations in triggering this growth. Due to momentum conservation, quasi-particles are created in pairs in two modes of opposite momentum. The characteristic signature of quantum vacuum fluctuations is then carried by the entanglement between these modes. The experimental observation of this entanglement is reported."