From microwave-shielded dimers to field-linked tetramers

Microwave-shielded polar molecules have emerged as a clean and highly tunable platform for studying ultracold chemistry and realizing exotic quantum matter with strong dipolar intereactions. Here, I will briefly review our efforts in understanding and controlling collisions of ultracold molecules, which in the end allow us to stabilize the molecular gas by microwave shielding and evaporate them to temperatures well below the Fermi temperature. The shape, symmetry, and depth of the intermolecular potential can be flexibly controlled by the microwave field, leading to field-linked resonances in collisions of polar molecules. It provides a universal tuning knob to independently control the dipolar interaction and contact interaction. In the end, I will present the creation of ultracold field-linked tetratomic molecules and highlight a few exciting possibilities, including dipolar BCS-BEC crossover and scalable assembly of larger molecules.