Photoionization of Neutral Barium and Biphoton Emission of Helium-like Ions

The combination of multichannel quantum-defect theory (MQDT) and the eigenchannel R-matrix method has been developed thoroughly throughout the years, allowing for the calculation of various observables for atoms and ions with two valence electrons. The present study employs a jj-coupling eigenchannel R-matrix code combined with MQDT to obtain a theoretical photoionization cross section for the 5d6p ³D^o₁ state of neutral barium (Ba). This theoretical work has been stimulated by experimental interest from the UCLA ion trapping groups of Eric Hudson and Wes Campbell. In another project involving two-electron atoms and ions, interest in a source of entangled XUV photon pairs for attosecond pump-probe experiments has recently led to a proposal for such biphoton pair creation through the decay of helium-like ion metastable states, and some of their competing decay processes will be discussed.[1]

[1] Phys. Rev. Research 4, L032038 (2022)