Degenerate photons from a cryogenic spontaneous parametric down-conversion source
N.A. Lange, T. Schapeler, J.P. Höpker, M. Protte, T. Bartley, Physical Review A 108 (2023).

Cryogenic integrated spontaneous parametric down-conversion
N.A. Lange, J.P. Höpker, R. Ricken, V. Quiring, C. Eigner, C. Silberhorn, T. Bartley, Optica 9 (2022).