Resonant-collision spectroscopy of Rydberg atoms

Resonant collisional energy transfer between atoms with small relative velocity is shown to have such long collision times, ~0.17 μs, or equivalently such narrow linewidths, 6 MHz, that it may be used to make spectroscopic measurements. Specifically, we report the use of the sharply resonant collisional energy transfer ns+(n-2)d-->np +(n-1)p, between velocity-selected K atoms to determine an improved value, 1.711 5(5), and the K np-state quantum defect.