Sub-Kelvin Thermometer for On-Chip Measurements of Microwave Devices Utilizing Two-Level Systems in Superconducting Microresonators

TL;DR

This paper introduces a superconducting microresonator thermometer based on two-level systems, capable of measuring on-chip temperatures from 50 mK to 1 K with high sensitivity, suitable for cryogenic microwave devices.

Contribution

The work presents a compact, compatible TLS-based thermometer for on-chip temperature measurement in cryogenic microwave systems, with demonstrated application in a kinetic inductance amplifier.

Findings

Achieved temperature measurement sensitivity of 50-75 μK/√Hz.

Operates effectively across 50 mK to 1 K range, extendable to 5 mK.

Successfully monitored static and transient heating in microwave devices.

Abstract

We present a superconducting microresonator thermometer based on two-level systems (TLS) that is drop-in compatible with cryogenic microwave systems. The operational temperature range is 50-1000~mK (which may be extended to 5~mK), and the sensitivity (50-75~$\mu$K/$\sqrt{\mathrm{Hz}}$) is relatively uniform across this range. The miniature footprint that conveniently attaches to the feedline of a cryogenic microwave device facilitates the measurement of on-chip device temperature and requires no additional thermometry wiring or readout electronics. We demonstrate the practical use of these TLS thermometers to investigate static and transient chip heating in a kinetic inductance traveling-wave parametric amplifier operated with a strong pump tone. TLS thermometry may find broad application in cryogenic microwave devices such as superconducting qubits and detectors.