Three Quanta Sensitivity Superconductor–Insulator–Superconductor Mixer for the 0.78–0.95 THz Band

We have successfully demonstrated a low-noise 0.78–0.95-THz waveguide mixer based on Nb/AlO x /Nb superconductor–insulator–superconductor (SIS) junctions integrated with an NbTiN/SiO 2 /Al superconducting inverted microstrip. The mixer employs a twin-junction tuning circuit and an impedance transformer which are designed to achieve both low noise and wideband operation. Corrected for optical input losses in front of the mixer, the double-sideband (DSB) noise temperature is below 120 K (<3 hf / k B ) around the local oscillator (LO) frequency of 0.88 THz and at an operating temperature of 2 K. The results represent state-of-the-art performance for mixers in the terahertz frequency range.