Open-source toolkit for calculating Rydberg atom interactions gets major upgrade

Rydberg atoms — hydrogen-like atoms with one electron promoted to a high-energy orbit — interact so strongly they can gate quantum logic operations, but modeling those interactions accurately requires handling both single-atom structure and geometry-dependent coupling simultaneously. This work combines multi-channel quantum defect theory, which captures the more complex electron structure of two-electron atoms like strontium and ytterbium, with a Green's tensor approach that naturally accounts for nearby surfaces or cavities. The updated PairInteraction software implementing this framework runs pair-potential calculations an order of magnitude faster than before, and produces Stark maps matching experimental ytterbium data. The open-source, modular design lets experimentalists extend the tool to new geometries and atom species.