Wideband frequency metrology using high temperature superconducting Josephson junctions

We have studied the responses of high temperature superconducting (HTS) Josephson junctions to monochromatic and polychromatic electromagnetic irradiations from 50 GHz to 4.25 THz. The highest operating frequency and the maximum value of normalized response are shown to be proportional to the I_CR_N product of the junction, where I_C and R_N are the critical current and normal resistance of the junction, respectively. Using a junction with I_CR_N of 330 μV, direct detections of monochromatic irradiations from 76 GHz to 3.1 THz have been obtained, indicating that fast detectors can be realized to cover around 50 : 1 frequency band by operating only one junction at one temperature. Also reported are the superposition of polychromatic signals, as well as some possible applications of the system.