Strongly quadrature-dependent noise in superconducting micro-resonators measured at the vacuum-noise limit

TL;DR

This study measures frequency and dissipation quadrature noise in superconducting micro-resonators near the vacuum noise limit, revealing significant frequency noise from two-level systems but negligible excess dissipation noise, impacting quantum device readout.

Contribution

First measurement of quadrature noise in superconducting resonators at vacuum noise sensitivity, showing dissipation noise is negligible at typical readout powers.

Findings

Frequency noise caused by two-level systems at 100 nW power.

No excess dissipation-quadrature noise observed above vacuum noise.

Results support low dissipation noise for quantum device applications.

Abstract

We measure frequency- and dissipation-quadrature noise in superconducting lithographed microwave resonators with sensitivity near the vacuum noise level using a Josephson parametric amplifier. At an excitation power of 100~nW, these resonators show significant frequency noise caused by two-level systems. No excess dissipation-quadrature noise (above the vacuum noise) is observed to our measurement sensitivity. These measurements demonstrate that the excess dissipation-quadrature noise is negligible compared to vacuum fluctuations, at typical readout powers used in micro-resonator applications. Our results have important implications for resonant readout of various devices such as detectors, qubits and nano-mechanical oscillators.