Superconducting microstrip amplifiers with sub-Kelvin noise temperature near 4 GHz

TL;DR

This paper reports a superconducting microstrip amplifier operating near 4 GHz with a noise temperature below 1 Kelvin, demonstrating potential for ultra-sensitive quantum measurements.

Contribution

The study introduces a novel SQUID-based microstrip amplifier with sub-Kelvin noise temperature at 3.8 GHz, using innovative measurement techniques.

Findings

Achieved a minimum system noise temperature of 0.55 K.

Demonstrated amplifier bandwidth of 150 MHz.

Validated measurement methods for low-noise superconducting amplifiers.

Abstract

We present measurements of an amplifier operating at 3.8 GHz with 150 MHz of bandwidth based on the microstrip input-coil resonance of a dc superconducting quantum interference device (SQUID) with submicron Josephson junctions. The noise temperature is measured using two methods: comparing the signal-to-noise ratio of the system with and without the SQUID in the amplifier chain, and using a modified Y-factor technique where calibrated narrowband noise is mixed up to the SQUID amplifier operating frequency. With the SQUID cooled to 0.35 K we observe a minimum system noise temperature of 0.55 $\pm~0.13$ K, dominated by the contribution from the SQUID amplifier.