Studies on Terahertz Photon Counting Detectors with Low-Leakage SIS Junctions

We plan to realize a fast terahertz photon counting detector. The detector may resolve each photon signal from the source and enable us to introduce “photon statistics,” which will be a new measure for terahertz astronomy and astrophysics. An SIS junction with Nb/Al/AlOx/Al/Nb is considered for this detector, which should incorporate low leakage current of 1 pA. We have successfully developed an SIS junction to satisfy this requirement. The bandwidth is limited, while it is sufficient for laboratory experiments. We have designed an antenna-coupled SIS detector incorporating the low-leakage SIS junction for photon counting experiments. Additionally, the photo-response of the SIS junction is measured to discuss the photon counting capability in combination with the fast readout system.