Bound-state-free AC/DC shielding of strongly dipolar ultracold molecules 

We propose a method to suppress collisional loss in strongly dipolar, rotationally excited ultracold molecules using a combination of static (dc) and microwave (ac) electric fields. By using a dc field to tune two excited pair molecular rotational states into a Förster resonance, an ac field can simultaneous be used to drive excited rotational transitions, removing all long-range bound states and allowing near complete suppression of all two- and three-body collisional loss channels. This bound-state-free ac/dc scheme is not subject to photon-changing collisions that are the primary source of two-body loss in shielding with two microwave fields, while permitting tunable dipolar and anti-dipolar interactions. This work opens new opportunities for realizing large, long-lived samples of strongly interacting molecular gases with tunable long-range interactions.