Quantum Gases of Dipolar Molecules: From Bose-Einstein Condensation to a Quantum Liquid

Ultracold quantum gases provide a powerful platform for exploring many-body physics with highly controllable interactions. In contrast to neutral atomic gases governed by short-range contact interactions, dipolar molecular gases introduce long-range and anisotropic interactions, opening a route to novel quantum phases inaccessible in atomic gases. In this seminar, I will present our experimental realization of a Bose-Einstein condensate (BEC) of sodium-cesium molecules, the first quantum-degenerate bosonic system of dipolar molecules. By dressing the molecules with microwave fields, we engineer intermolecular potentials with controllable anisotropy and strength, while suppressing collisional loss below the detection limit. With increasing interaction strength, the system exhibits a rich evolution of behavior. In the weakly interacting regime, the condensate undergoes electrostriction, an anisotropic deformation of its shape driven by dipolar interactions. At stronger interactions, we observe the emergence of complex density structures, eventually entering the regime of self-bound droplets—a quantum liquid phase stabilized by interactions. The observed droplet densities are up to two orders of magnitude higher than those of weakly dipolar condensates. In this regime, the relevant interaction length scale exceeds the interparticle spacing, placing the system in the strongly interacting regime. As an outlook, I will discuss how molecular BECs can serve as a platform for quantum simulation of lattice systems and for probing strongly correlated quantum matter.