Anomalous Lifetimes of Ultracold Complexes Decaying into a Single Channel: What's Taking So Long in There?

Abstract

We investigate the lifetimes of complexes formed in ultracold molecule collisions. Employing both transition-state-theory and an optical model approach we examine processes that can extend the lifetime of complexes beyond that predicted by Rice-Ramsperger-Kassel-Marcus theory. We focus on complexes that possess only one open channel, and find that the extreme distribution of widths for this case favors low decay rates. Thus decay from a complex into a single energetically available channel can be anomalously slow, and moreover nonexponential in time. We apply the theory to two systems of current experimental interest, RbCs and NaRb, finding qualitatively that the empirical time scales can be accounted for in the theory.

Symmetry breaking in sticky collisions between ultracold molecules

“…1. This analysis provides support for the physical picture proposed by Mayle et al [30,31] of classically chaotic dynamics, as subsequently assumed in further work [34][35][36][37].…”

“…During these sticky collisions the molecules are vulnerable to collisions with a third body [30][31][32] or photoexcitation by the trapping laser [33]. This work has shaped the way the field thinks about collisional loss [34][35][36][37], although the debate is not settled on even the order of magnitudes of sticking times [38], nor on what physical loss processes might occur during that time. Some of the present authors have proposed a theoretical framework to compute the density of states of ultracold collision complexes [32], and the rate of loss by photoexcitation of these complexes by the trapping laser [33].…”

Ultracold Sticky Collisions: Theoretical and Experimental Status

“…Given this mechanism, the rate equations for the molecule and complex populations ( n and n c ) take the form ṅ = prefix− k 2 n 2 + 2 C − 2 n c τ RRKM ṅ c = k 2 n 2 2 − C − 2 n c τ RRKM − k I I n c Here, k 2 is the molecular scattering rate coefficient, k I is the laser excitation rate coefficient, I is the laser intensity, and C –2 is a factor which originates from quantum defect theory and describes the probability to cross the long-range part of the potential. ,, This factor C –2 is implicitly also included in k 2 and will be described in more detail in Section . To accurately describe experimental data, it is often necessary to also model effects resulting from inhomogeneous density distribution, one-body loss, and evaporation. , …”

“…Even when sampling over many resonances, this could still have an impact on the actual loss rate. However, the estimated increase in sticking time from ref is not sufficient to explain the experimental results.…”

Microscopy of an ultranarrow Feshbach resonance using a laser-based atom collider: A quantum defect theory analysis

“…Extraordinarily long lifetimes, approaching milliseconds [7][8][9], have been observed in collisions between nonreactive ultracold molecules in their absolute ground state. These long lifetime have been attributed to the high density of states of molecules [10][11][12] and suggest the presence of overlapping resonances [13]. Interacting Feshbach resonances are also of importance in collisions of ultracold magnetic lanthanides, such as erbium and dysprosium, and have been used to reveal the chaotic nature of the collision process [14,15].…”