Fig. 1

A Josephson platform for waveguide quantum electrodynamics. a Lumped-element model of the circuit including the nodes used in the calculations. b Optical microscope image of the sample. The two zoom-in are SEM pictures of the SQUID of the qubit (red square) and the SQUIDs in the chain (blue square). The qubit is capacitively coupled to the chain and to a 50 Ω measurement line, via large interdigital contacts. Only a small portion of the Josephson chain, which comprises 4700 SQUIDs in total, is shown