Microscopic Origin of Emergent Elliptic Flow and Molecule Formation in Strongly Interacting Quasi-Two-Dimensional Few-Body Systems

Abstract

Recent experiments simulating two-dimensional few-fermion systems have observed emergent hydrodynamic behavior, i.e., interaction-driven elliptic flow by adding fermions two at a time [S.~Brandstetter et al., Nat. Phys. (2025)]. Due to the curse of dimensionality and strong correlations, capturing such phenomena beyond two particles remains challenging. Here, we use the ab initio time-dependent explicitly correlated Gaussian (TDECG) method to quantitatively reproduce these experimental observations. With only a moderate number of correlated Gaussian basis functions, our approach obtains converged dynamical observables for systems up to six particles. Furthermore, real-time access to the many-body wavefunction and two-point correlation functions enables us to visualize the transformation from a strongly interacting gas to a stream of paired molecules, i.e., a dynamical BCS-BEC crossover.