Fig. 2: dc and ac Josephson effect of the individual junctions.
From: Charge-4e supercurrent in a two-dimensional InAs-Al superconductor-semiconductor heterostructure
a, b Differential resistance dV/dI of the individual Josephson junctions JJ1 and JJ2 as a function of gate voltage VG1, VG2 and current bias I. c, d Integrated voltage Vint as a function of current bias I at VG1 = −0.75 V and VG2 = −0.7 V obtained by integrating the corresponding dV/dI along the white dashed lines shown in a, b. e Illustration of the expected peak evolution in the emission spectrum of voltage-biased JJ as a function of detection frequency \({f}_{\det }\). A junction with finite transparency emits photons at the fundamental Josephson frequency (red dashed line) and integer multiples of it (orange and pink dashed lines), here corresponding to the coherent transport of pairs of Cooper-pairs. The dashed gray lines indicate processes associated with the up- and down-conversion of environmental photons at frequency fenv. f, g Normalized radiation power Pdet,norm. as a function of \({f}_{\det }\) and Vint for the same configuration in c and d. The orange arrow points to the 4e emission peak.
