Fig. 4: Up- and down-conversion of Josephson photons into multiple modes.
a Illustration of the up- and down-conversion. A comb spectrum (red) is obtained at Vdc = 36.39 μV, corresponding to a Josephson frequency of 17.6 GHz. b–d Coherent injection-locking effects with msen = 7 and for injections at minj = 1 (b), 6 (c), and 54 (d), respectively. The dashed lines are fittings to extend Alder’s Eq. (2).
