The Study of Thermal Fluctuations in Microwave and Mechanical Resonators

TL;DR

This paper presents a high-resolution dual-channel measurement system for thermal fluctuations in microwave and mechanical resonators, demonstrating significant noise suppression and improved detection contrast, with potential applications in dark matter searches.

Contribution

The study introduces a dual-channel readout system that suppresses amplifier noise, enhancing thermal noise detection in resonators, a novel approach for high-precision fluctuation measurements.

Findings

Over 16 dB improvement in thermal noise peak contrast

Effective suppression of amplifier's intrinsic fluctuations

Enhanced discrimination of fluctuation types for dark matter detection

Abstract

We report high-resolution measurements of thermal fluctuations in microwave and mechanical resonators using a dual-channel readout system. The latter comprises a low-noise amplifier, an I/Q-mixer, and a cross-correlator. We discovered that, under certain conditions, the intrinsic fluctuations of the low-noise amplifier, which are common to both channels of the readout system, are averaged out when computing the voltage noise cross-spectrum between the mixer's outputs. The suppression of the amplifier's technical fluctuations significantly improves the contrast of the thermal noise peaks exhibited by the resonators. Thus, for the room-temperature-stabilized 9 GHz sapphire-loaded cavity resonator, we observed more than 16 dB improvement in the thermal noise peak contrast relative to the single-channel measurements. The ability of the dual-channel readout system to discriminate between the broad- and narrow-band fluctuations may benefit the search for dark matter, which relies on the use of cryogenic microwave resonators.