Non-adiabatic quantum effects in ultracold K + KRb → K₂ + Rb chemical reaction

More than a decade since the first measurement of the K + KRb(X¹Σ⁺,ν=0,N=0) ultracold chemical reaction at JILA [1], characterized by a rate constant of 1.7×10^-10 cm³/s at about 250 nK, a theoretical study of this reaction remains a challenging endeavor. The only full-dimensional quantum reactive scattering simulation corresponds to that of Croft et al. [2]. The theoretical rate constant of Croft et al. underestimates the measurement value by about 35% but agrees with the value predicted by a universal model based purely on long-range forces. A possible source of the discrepancy is the neglect of the non-adiabatic coupling between the two lowest electronic states of the triatomic complex, coupled through a conical intersection at short ranges. In this work we account for the non-adiabatic effect in a diabatic representation of the coupled electronic states. We will discuss the methodology implemented in hyperspherical coordinates [3] and the possible role of quantum interference effects mediated by the conical intersection in bridging the gap between theory and experiment.