Optical Performance of SIS Photon Detectors at Terahertz Frequencies

Fast photon detectors will be one of the key technologies to introduce new observing methods. Utilizing our recent development of low leakage SIS junctions with Nb/Al/AlOx/Al/Nb, we designed and fabricated an antenna-coupled SIS detector. The detector exhibited a leakage current of 2 pA at $$ T \le 0.8\,{\text{K}} $$ . Fourier transform spectrometer measurements show a clear resonance peak, although the peak frequency and bandwidth were shifted from the designed values. Even though the detector efficiency was low, the noise measurement suggests that the detector would allow us to read out single terahertz photon by introducing the photon-counting scheme.