Radiatively-cooled quantum microwave amplifiers

TL;DR

This paper introduces a radiatively-cooled quantum microwave amplifier using high-temperature superconducting NbN, achieving near-quantum-limited noise performance at 1.5 Kelvin, which simplifies cooling requirements for quantum technologies.

Contribution

The work demonstrates a high-performance, radiatively-cooled microwave amplifier based on NbN, operating effectively at elevated temperatures, advancing scalable quantum readout technology.

Findings

Achieves 1.3 quanta of added noise at 1.5 Kelvin

Maintains high gain comparable to low-temperature amplifiers

Operates with only 0.2 quanta increase in noise from 0.1K to 1.5K

Abstract

Superconducting microwave amplifiers are essential for sensitive signal readout in superconducting quantum processors. Typically based on Josephson Junctions, these amplifiers require operation at milli-Kelvin temperatures to achieve quantum-limited performance. Here we demonstrate a quantum microwave amplifier that employs radiative cooling to operate at elevated temperatures. This kinetic-inductance-based parametric amplifier, patterned from a single layer of high-$T_\mathrm{c}$ NbN thin film\cmt{in the form of a nanobridge}, maintains a high gain and meanwhile enables low added noise of 1.3 quanta when operated at 1.5 Kelvin. Remarkably, this represents only a 0.2 quanta increase compared to the performance at a base temperature of 0.1 Kelvin. By uplifting the parametric amplifiers from the mixing chamber without compromising readout efficiency, this work represents an important step for realizing scalable microwave quantum technologies.