Strong enhancement of Penning ionization for asymmetric atom pairs in cold Rydberg gases: The Tom and Jerry effect

We consider Penning ionization of Rydberg atom pairs as an Auger-type process induced by the dipole-dipole interaction and employ semiclassical formulae for dipole transitions to calculate the autoionization width as a function of the principal quantum numbers, n _d, n _i, of both atoms. While for symmetric atom pairs with the well-known increase of the autoionization width with increasing n ₀ is obtained, the result for asymmetric pairs is counterintuitive - for a fixed n _i of the ionizing atom of the pair, the autoionization width strongly increases with decreasing n _d of the de-excited atom. For H Rydberg atoms this increase reaches two orders of magnitude at the maximum of the n _d dependence, and the same type of counterintuitive behavior is exhibited also by Na, Rb and Cs atoms. This is a purely quantum-mechanical effect, which points towards existence of optimal (we call them 'Tom' and 'Jerry' for 'big' and 'small') pairs of Rydberg atoms with respect to autoionization efficiency. Building on the model of population redistribution in cold Rydberg gases proposed in [1], we demonstrate that population evolution following the initial laser excitation of Rydberg atoms in state n ₀ would eventually lead to the formation of such Tom-Jerry pairs with which feature autoionization widths that are enhanced by several orders of magnitude compared to that of two atoms in the initial laser-excited state n ₀. We also show that in the high-density regime of cold Rydberg gas experiments the ionization rate of Tom-Jerry pairs can be substantially larger than the blackbody radiation-induced photoionization rate.