Speaker: Dr. Zhenjie Yan, Univ. California Berkeley
Abstract: From the persistent electric currents in superconductors to the synchronized motion of a flock of birds, emergent collective behaviors arise ubiquitously from the interactions between constituents in many-body ensembles. Ultracold atom experiments, with their precisely tunable interactions and well-controlled initial states, provide a powerful platform to explore these cooperative phenomena in quantum many-body systems. In this talk, I will present examples of collective effects in both macroscopic and mesoscopic regimes, drawn from my recent works. First, I will discuss thermal transport in a macroscopic strongly interacting Fermi gas, a system that poses significant challenges for existing theoretical and computational methods. The heat transport reveals a striking signature of a superfluid phase transition: while heat propagates diffusively in the normal phase, it propagates as a wave—known as second sound—below the superfluid transition temperature. Next, I will introduce recent work on constructing a mesoscopic system atom-by-atom using optical tweezers, with precise control over interactions mediated by photon exchange in an optical cavity. This platform enables the study of self-organization and symmetry breaking. The atom array reveals distinctive hallmarks of mesoscopic physics, such as the dependence of the critical point and the state lifetime on the system size. Finally, I will briefly outline my future research plans to develop quantum systems that are robust against noise and decoherence using atoms and light for emulating many-body systems and carrying out computational tasks.