Rotational quenching of monofluorides in a cryogenic helium bath*

Ultracold polar molecules provide a versatile platform for advancing quantum sciences and technologies [1]. Among direct cooling techniques, buffer gas cooling plays a critical role in achieving efficient laser cooling of dipolar molecules to sub-microkelvin temperatures [2]. The efficiency of this method strongly depends on the thermalization and energy transfer mechanisms in atom-molecule collisions [3]. In this work, we present a detailed study of the rotational quenching dynamics of monofluoride molecules (X-F), where X is an alkaline-earth metal or metal, in collisions with cryogenic helium. Within a multi-channel scattering framework, using ab inito potential energy surfaces, we compute state-tostate rotational cross-section and transport properties relevant for buffer gas cooling experiments. Our findings reveal a general expression that connects rotational quenching efficiency to intrinsic molecular properties and long-range interaction coefficients, applicable to any atom-molecule system.

[1] J. L. Bohn, A. M. Rey, and J. Ye, Cold molecules: Progress in quantum engineering of chemistry and quantum matter, Science 357, 1002 (2017).

[2] S. F. Vázquez-Carson, Q. Sun, J. Dai, D. Mitra, and T. Zelevinsky, Direct laser cooling of calcium mono-hydride molecules, New Journal of Physics 24, 083006 (2022)

[3] N. R. Hutzler, H.-I. Lu, and J. M. Doyle, The buffer gas beam: An intense, cold, and slow source for atoms and molecules, Chemical Reviews, Chemical Reviews 112, 4803 (2012).