Low-noise microwave amplifier utilizing superconductor-insulator-superconductor junction

A low-noise microwave amplifier utilizing a superconductor-insulator-superconductor junction, the low-noise microwave amplifier comprising a circuit in which two quasiparticle mixers each utilizing the superconductor-insulator-superconductor junction are connected in tandem or in cascade,

• wherein a first quasiparticle mixer performs first frequency mixing with use of a first local oscillation signal having a frequency not less than twice a frequency of an input signal to the first quasiparticle mixer, a second quasiparticle mixer performs second frequency mixing with use of a second local oscillation signal having a frequency not more than twice a frequency of an input signal to the second quasiparticle mixer, and signal amplification is performed with a conversion gain obtained through frequency conversion by outputting, from among a plurality of signals generated with the first frequency mixing and the second frequency mixing, a signal in a frequency band not more than a frequency band of the signal before being subjected to the first frequency mixing and the second frequency mixing.