Strongly driven Kerr oscillator based on Ne-FIB milled Nb nanobridges

Nonlinear microwave circuits have a wide range of potential applications in quantum computing, quantum sensing, and in the readout of weak microwave signals arising from certain fundamental physics experiments. Such devices can be realised from Josephson junction-based devices embedded in a frequency-tunable resonator that is both resilient to magnetic field and able to operate in wide temperature ranges. These requirements motivate the use of a higher H_c superconducting metal such as niobium. Typically, such devices utilise conventional tri-layer sandwich-type Josephson junctions, whereas we use single-layer niobium nanobridge structures as the weak links, offering a simpler fabrication process and potentially higher operational frequency compared to multilayer devices. In this work we investigate Kerr-type non-linearity and four-wave mixing in a λ/4 coplanar-waveguide (CPW) resonator terminated with a DC nanoSQUID. We present the use of two-tone spectroscopy to study the shift in resonant frequency of the high-Q Josephson CPW resonator under the application of a drive signal. With a strong applied drive above the bifurcation threshold, we observe the presence of signal and idler sidebands occurring via the four-wave-mixing process. We discuss the microwave response and gain of the device at 15 mK as a function of drive frequency, drive power, and applied magnetic field, and show that the device has potential application as a quantum amplifier even in background fields of order 10 mT.