On-chip coil-integrated STJ using the persistent superconducting current for photon detectors

A superconducting tunnel junction (STJ) is very attractive for use in high-energy-resolution photon detectors because of its small energy gap. To detect a single photon, the Josephson current of the STJ has had to be suppressed by an external magnetic field. We demonstrated an on-chip coil-integrated STJ photon detector, which excludes the external magnetic field, allowing a small device size. A normal-distribution function shape was adopted for the superconducting electrodes, which makes the magnetic field supplied to the STJ small. We devise a new superconducting photon detector by combining the above techniques. A new Josephson switching gate is also integrated on the same detector chip in order to drive an on-chip integrated coil by a persistent superconducting current. This behavior was confirmed experimentally using the technology of the fabrication process of the Nb/Al-AlOx/Nb Josephson tunnel junction.