Non-Adiabatic Quantum Dynamics of Ultracold Collisions of Rb with KRb

Inspired by a recent ultracold experiment[1] on non-reactive Rb + KRb collisions that reports universal two-body trap losses and long-lived KRb2 collision complexes, we perform the first-principle quantum dynamics calculations for ultracold collisions of Rb with KRb in its ground rovibrational state. Accurate ab-initio electronic potential energy surfaces are used, which include both the ground and first excited electronic states. Both electronic states are energetically accessible within the interaction region and must be included in the quantum dynamics calculations even at ultracold collision energies. The two electronic states become degenerate and exhibit a conical intersection that leads to significant non-adiabatic quantum interference effects.[2] In addition, the excited electronic state potential energy surface supports bound states that can lead to long-lived collision complexes (Feshbach resonances), which may be responsible for the unexplained long lifetimes observed by [1]. Elastic cross sections and time-delays are reported as a function of collision energy from 1 nK to 1 K using a high resolution energy grid. Intriguing non-adiabatic quantum interference and resonance effects are reported that lead to significant enhancement and suppression of the cross sections providing unique insight into the mechanisms of ultracold collisions and complex formation.

[1] M. A. Nichols, et. al, Phys. Rev. X 12, 011049 (2022)

[2] B. K. Kendrick, et. al, Phys. Chem. Chem. Phys. 23, 5096 (2021)