On March 25, Gabriel G.T. Assumpção successfully defended the thesis “Thermodynamics and Dynamics of Quantum Fermi Gases in a Piston of Light” (advisor: Nir Navon).
Assumpção explained, “We are living through what some have called a second quantum revolution, in which new and powerful technologies are giving us greater control and deeper insight into quantum matter. Throughout my PhD, I had the special opportunity to help assemble a new apparatus capable of creating programmable, homogeneous quantum matter by trapping ultracold gases of lithium-6 in microscopic optical “boxes,” a capability shared by only a handful of labs worldwide. I focused on dynamically changing the shape of these boxes, which allowed me to study not only the foundational Joule expansion process in degenerate Fermi gases, but also the dynamics of their free expansion. I also pushed the limits of our current apparatus, particularly of the essential digital micromirror devices (DMDs) we use, in pursuing quasi-static thermodynamic transformations of the trapped gases. I hope that identifying these limitations will help further enhance the already impressive versatility of DMDs, pushing the field of quantum simulation even further.”
Assumpção will continue with Prof. Navon’s group as a postdoc, where he will work on new dynamic experiments with the homogeneous ultracold fermionic gases.
Thesis Abstract
We report thermodynamic and dynamical measurements of a degenerate Fermi gas in a homogeneous optical box trap realizing a piston of light. Fast control of the piston using digital micromirror devices enabled Joule expansion experiments in weakly interacting and unitary Fermi gases, where opposite temperature changes consistent with their Joule coefficients were observed. Time-resolved measurements showed ballistic expansion for the ideal gas and self-similar front dynamics in the unitary gas consistent with Euler hydrodynamics. We also investigated the effects of piston velocity, wall softness, and micromirror flickering on achieving adiabatic transformations of the trapped gases. These results identify limitations to quasi-static transformations and demonstrate dynamical optical box traps as a promising platform for quantum simulations.
Thesis Committee: Nir Navon (advisor), Charles Brown, Yoram Alhassid, Steve Lamoreaux, and Frederic Chevy (ENS, France)