Flux-driven Josephson parametric amplifier for sub-GHz frequencies fabricated with side-wall passivated spacer junction technology

TL;DR

This paper reports on a flux-driven Josephson parametric amplifier optimized for sub-GHz frequencies, demonstrating high gain, tunability, and low noise, suitable for ultra-sensitive microwave detection.

Contribution

It introduces a novel fabrication technique using side-wall passivated spacer junctions that enhances performance and temperature robustness of the amplifier.

Findings

Gain exceeds 20 dB in three-wave mixing

Center frequency tunable between 540 MHz and 640 MHz

Adds 105 mK of noise at 600 MHz

Abstract

We present experimental results on a Josephson parametric amplifier tailored for readout of ultra-sensitive thermal microwave detectors. In particular, we discuss the impact of fabrication details on the performance. We show that the small volume of deposited dielectric materials enabled by the side-wall passivated spacer niobium junction technology leads to robust operation across a wide range of operating temperatures up to 1.5 K. The flux-pumped amplifier has gain in excess of 20 dB in three-wave mixing and its center frequency is tunable between 540 MHz and 640 MHz. At 600 MHz, the amplifier adds 105 mK $\pm$ 9 mK of noise, as determined with the hot/cold source method. Phase-sensitive amplification is demonstrated with the device.