Creating Feshbach resonances for ultracold molecule formation with radiofrequency fields

TL;DR

This paper demonstrates that radiofrequency radiation can be used to create tunable Feshbach resonances in ultracold alkali-metal gases, enabling controlled molecule formation at convenient magnetic fields.

Contribution

It introduces a method to generate Feshbach resonances using RF fields in cases where none exist without RF, specifically for $^{39}$K+$^{133}$Cs.

Findings

RF can create near-ideal Feshbach resonances at specific magnetic fields.

Long-lived molecules can be formed even with plane-polarized RF.

Resonances are almost lossless with circular polarization.

Abstract

We show that radiofrequency (RF) radiation may be used to create Feshbach resonances in ultracold gases of alkali-metal atoms at desired magnetic fields that are convenient for atomic cooling and degeneracy. For the case of $^{39}$K+$^{133}$Cs, where there are no RF-free resonances in regions where Cs may be cooled to degeneracy, we show that a resonance may be created near 21~G with 69.2~MHz RF radiation. This resonance is almost lossless with circularly polarized RF, and the molecules created are long-lived even with plane-polarized RF.