Bound-state-free F\"orster resonant shielding of strongly dipolar ultracold molecules

TL;DR

This paper introduces a novel method combining static and microwave electric fields to suppress collisional loss in ultracold dipolar molecules, enabling stable, long-lived molecular gases with tunable interactions.

Contribution

The authors propose a bound-state-free shielding scheme using ac/dc fields to eliminate bound states and suppress collisional loss in strongly dipolar molecules, a significant advancement over previous microwave-only methods.

Findings

Achieves elastic-to-loss rate ratios >10^6 at 100 nK

Removes long-range bound states to suppress collisional channels

Demonstrates feasibility with NaCs molecules using current technology

Abstract

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 tuning two excited pair molecular rotational states into a F\"orster resonance with a dc field, simultaneously driving excited rotational transitions with an ac field removes all long-range bound states, allowing near complete suppression of all two- and three-body collisional loss channels. While permitting tunable dipolar and anti-dipolar interactions, 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, used to achieve the first molecular Bose-Einstein condensate [Bigagli et al., Nature 631, 289 (2024)]. Using NaCs as a representative example for strongly dipolar molecules, close-coupling calculations are performed to show that bound-state-free shielding can achieve ratios of elastic-to-loss rates $\gtrsim 10^{6}$ at 100 nK, with currently accessible ac and dc field generation technologies. This work opens new opportunities for realizing large, long-lived samples of strongly interacting degenerate molecular gases with tunable long-range interactions.