Determination of Cooper minima and shape resonances of nS and nD Rydberg states in Rb and Cs

Rydberg atoms generally become less sensitive to photoionization (PI) as the photon energy increases due to an increasing mismatch between bound-state and free-electron wavefunctions. However, in certain PI channels this trend is interrupted by pronounced minima in the PI cross sections. Here we present calculations of the PI cross sections in both rubidium and cesium Rydberg atoms over a wavelength range from the infrared to the ultraviolet, using model potentials from [M. Marinescu, H. R. Sadeghpour, and A. Dalgarno, Phys. Rev. A 49, 982 (1994)]. The resulting cross sections exhibit both broad PI minima in the nS to ϵP PI channels of both Rb and Cs (with free-electron energy ϵ) identified as Cooper minima, and much narrower features in the nD to ϵF channels due to shape resonances of the free-electron states. The small total PI cross sections of these states make them ideal for applications of optically excitable laser-trapped Rydberg atoms. Examples of applications include quantum simulation, quantum information processing and high-precision spectroscopy.