Integrated conversion and photodetection of virtual photons in an ultrastrongly coupled superconducting quantum circuitLuigi Giannelli, Giorgio Anfuso, Miroslav Grajcar, Gheorghe Sorin Paraoanu, Elisabetta Paladino and Giuseppe FalciEur. Phys. J. Spec. Top., 232 20-22 (2023) 3387-3392DOI: https://doi.org/10.1140/epjs/s11734-023-00989-0