Fabrication and Evaluation of Waveguide Josephson Array Oscillators at Millimeter-Wave Lengths for SIS Mixer-Based Amplifiers

In this study, a 150 GHz waveguide Josephson array oscillator was designed, fabricated, and evaluated as a local oscillator (LO) source for superconductor-insulator-superconductor (SIS) mixer-based amplifiers. These amplifiers aim to reduce the power consumption of microwave amplifiers used in large-scale multi-pixel heterodyne receivers for radio astronomy and superconducting quantum computers. We fabricated a Josephson array oscillator of 11 Nb/Al–AlO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub>/Nb Josephson junctions with Cu shunt resistors, each of which is placed on the center of a half-wavelength microstrip line resonator. When the LO signal from the oscillator was introduced into the balanced SIS mixers via a waveguide, the oscillator successfully pumped four SIS mixers simultaneously, delivering a total estimated LO power of 0.22 µW at 146.7 GHz. The SIS mixers operated without a millimeter-wave isolator at an LO noise temperature of 4–6 K. These results indicate the Josephson array oscillator's potential as an LO source for SIS mixer-based amplifiers.