A Novel Three-Body Heating Effect in Microwave-Shielded Dipolar Molecules*

Loss in trapped samples of ultracold molecules can be dramatically reduced via collisional shielding. In all shielding approaches, the shielded molecular state constitutes an excited metastable internal state. While this state can be long-lived, decay out of this state opens a channel for inelastic loss, releasing energy. Even when the energy released is sufficient to eject a pair of molecules from the trap, the escaping molecules can elastically collide with the dense molecular sample, heating it, a process we call “microwave-induced three-body heating”. Building on precise methods for characterizing the losses in trapped molecular samples, we observe and characterize the residual heating in trapped gases of NaCs molecules. The measured heating rates align with ab initio predictions and we extrapolate our results to other molecules [1]. While the related heating rates are small, they are relevant for molecular BECs in the nanokelvin regime [2]. Understanding this mechanism is key to mitigation and to further enhance the lifetime of degenerate quantum liquids of dipolar molecules. 

[1] Karman, T., et al. Double microwave shielding. arXiv 2501.08095 (2025).

[2] Bigagli, N., Yuan, W., Zhang, S. et al. Observation of Bose–Einstein condensation of dipolar molecules. Nature 631, 289–293 (2024).