Self-Bound Droplets of Ultracold Dipolar Molecules under Tunable Double Microwave Shielding

Abstract

We use the Ground-State Path Integral Monte Carlo method to study a Bose-Einstein condensate of strongly interacting NaCs polar molecules under the action of a fully anisotropic double microwave shielding potential characterized by a linear and an elliptical polarization field. In particular, we analyze the ground state of the system and its structure as a function of the ellipticity angle $\xi$. While for the circularly polarized case ($\xi=0$) a gas phase is realized, one or more self-bound droplets are observed for small $|\xi|$'s above a threshold value near $3^\circ$. With increasing $\xi$, the observed droplets rapidly become tightly bound and are estimated to form a superfluid array. Our results compare favorably to the experimental observations in [Zhang et al., Nature \textbf{651}, 601 (2026)] for positive $\xi$, while moderate differences show up for $\xi<0$ where our simulations conform to the expected symmetries of the intermolecular potential.