  We perform two-tone spectroscopy on quantum circuits, where high-frequency
radiation is generated by a voltage-biased superconductor-normal-superconductor
Josephson junction and detection is carried out by an ancillary microwave
resonator. We implement this protocol on two different systems, a transmon
qubit and a $\lambda/4$ resonator. We demonstrate that this two-tone Josephson
spectroscopy operates well into the millimeter-wave band, reaching frequencies
larger than 80 GHz, and is well-suited for probing highly coherent quantum
systems.
