Probing van der Waals interactions and detecting polar molecules by F\"orster resonance energy transfer with Rydberg atoms at temperatures below 100 mK

TL;DR

This study demonstrates electric-field-controlled F"orster resonance energy transfer between Rydberg helium atoms and ground-state ammonia molecules at ultra-cold temperatures below 100 mK, revealing insights into van der Waals interactions and enabling non-destructive molecule detection.

Contribution

It introduces a novel method to probe van der Waals interactions and detect polar molecules using F"orster resonance energy transfer with Rydberg atoms at ultra-cold temperatures.

Findings

Resonance widths as low as 100 MHz observed for Rydberg-Rydberg transitions.

Van der Waals interactions increased resonance widths to around 750 MHz.

NH$_3$ density measured non-destructively at approximately 9.4×10^9 cm$^{-3}$.

Abstract

Electric-field-controlled F\"orster resonance energy transfer (FRET) between Rydberg helium (He) atoms and ground-state ammonia (NH$_3$) molecules has been studied at translational temperatures below 100 mK. The experiments were performed in an intrabeam collision apparatus with pulsed supersonic beams of NH$_3$ seeded in He. A range of F\"orster resonances, between triplet Rydberg states in He with principal quantum numbers of 38, 39 and 40, and the inversion intervals in NH$_3$ were investigated. Resonance widths as low as $100\pm20$ MHz were observed for Rydberg-Rydberg transitions with electric dipole transition moments of 3270 D. These widths result from binary collisions at a mean center-of-mass speed of $19.3\pm2.6$ m/s. For transitions in which the initially prepared Rydberg states were strongly polarized, with large induced static electric dipole moments, van der Waals interactions between the collision partners increased the resonance widths to $\sim750$ MHz. From measurements of the rate of FRET for the narrowest resonances observed, a density of NH$_3$ of $(9.4\pm0.3)\times10^{9}$ cm$^{-3}$ in the upper ground-state inversion sublevel in the interaction region of the apparatus was determined non-destructively.