Center for Quantum Dynamics Colloquium

Quantum mixtures of different atomic species represent compelling frameworks for a variety of fundamental studies and quantum-technological applications, ranging from the exploration of exotic few- and many-body phenomena to the realization of novel molecular species in the ultracold regime.

Here, I will first provide a general overview of the activities of our lab, primarily based on a novel Fermi-Fermi mixture of ⁶Li alkali and ⁵³Cr transition-metal atoms, and currently focusing onto two main research topics: realization of quantum gases of LiCr molecules, and investigation of strongly interacting fermionic matter in presence of a large mass asymmetry.

I will then discuss in more detail a recent study of transport dynamics of a small sample of ultracold lithium atoms – acting as light impurity particles – released into a large, ideal gas of chromium – that plays the role of a bath of heavy, point-like scatterers. Under strong interspecies interactions, by lowering the temperature we unveil a crossover from normal diffusion to subdiffusion. Simultaneously, a localized fraction emerges in the lithium gas, displaying no discernible dynamics over hundreds of collision events. Our findings, incompatible with a conventional Fermi-liquid picture, are instead captured by a model of a matter wave propagating through a (quasi-)static disordered landscape of point-like scatterers. These results point to a key, enhanced role of quantum interference in heavy-light atomic mixtures, which emerge as versatile platforms for exploring disorder-free localization phenomena solely driven by a large mass difference.

The localization-delocalization transition in disordered media is ubiquitous in quantum and classiacal systems. It is one of the rare transition for which there is no mean-field theory valid in any dimensions. We report the observation and characterization of the Anderson transition in 4D using ultracold atoms as a quantum simulator with synthetic dimensions.

We will give a pedagogical introduction to disordered quantum systems and their quantum simulation with Floquet driving. We will then characterize the universal dynamics in the vicinity of the phase transition and measure the critical exponents describing the scale-invariant properties of the critical dynamics.

Quantum vortices are among the most prominent examples of topological excitations in superfluids. They arise in both bosonic systems, such as superfluid helium-4 and atomic Bose–Einstein condensates, and in fermionic systems, including superfluid helium-3, metallic superconductors, and neutron matter. While topology constrains many of their properties, key aspects of vortex behavior are governed by their internal structure, which depends on quantum statistics. In this seminar, I will review recent studies of quantum vortices in Fermi superfluids and contrast them with their bosonic counterparts. Particular attention will be given to the evolution of vortex core structure across the BCS–BEC crossover, spanning the transition from weak to strong coupling. I will then discuss how these structural changes influence vortex dynamics, focusing on the emergence of vortex inertia in Fermi systems and on microscopic mechanisms responsible for dissipation in their motion. The discussion will be supported by numerical results from density functional theory for Fermi superfluids, along with comparisons with experimental results for ultracold Fermi gases.