Microwave amplification by using Niobium-based Josephson-junction array parametric oscillator

Quantum parametric oscillators are essential tools for generating and manipulating quantum states, with applications in quantum communication, quantum sensing, and quantum computation. We report the realization of microwave quantum parametric oscillations within the 4 to 8 GHz range using a Niobium-based Josephson-junction array (JJA). Each junction is defined by a circular area of 3 μm in diameter, chosen based on theoretical modeling to meet the desired nonlinear and dynamic range characteristics, while also relaxing lithographic constraints. The JJA consists of 30 to 400 Josephson junctions, each coupled with a parallel capacitor to form a transmission line with 20-Ohm impedance, and is embedded in an external 50-Ohm transmission line, creating an impedance-mismatched resonator. We observe parametric amplification with a gain of up to ~10 dB over a tunable frequency range within the 4 to 8 GHz pump band, with saturation near -100 dBm. Theoretical analysis based on a nonlinear circuit model suggests that the observed behavior arises from parametric oscillations linked to amplification. Our findings demonstrate a novel method for implementing a parametric oscillator with tunable amplification, offering potential applications in quantum sensing, illumination, and qubit readout.