I am a computer scientist specialising in quantum information processing.
I am currently struggling to understand the photonic setting in the figure below (coming from this paper).
I wonder how a standard generic input $\alpha|\texttt{0}\rangle + \beta|\texttt{1}\rangle$ -- figure (a) -- maps to what it looks to me as a fixed input of two EPR pairs $|\Phi^{\texttt{+}}\rangle \otimes |\Phi^{\texttt{+}}\rangle$ -- figure (b) --.
I am not really used to read photonic settings. E.g. I don't know what is meant for trigger, nor for $e_i, o_i$.