Useful idea buried under abject science-writing is that

quantum yields quantify how likely a chain reaction is. It's like r for COVID-19. One usually says "1.3", not "130%"

Quantum yields greater than 1 are possible for photo-induced or radiation-induced chain reactions, in which a single photon may trigger a long chain of transformations

https://en.wikipedia.org/wiki/Quantum_yield#:~:text=Quantum%...

Diagram from the paper showing the initiation of a light-generated "avalanche"

https://xcancel.com/YoichiSasaki1/status/2036808566011789536