How do you determine whether cosmic rays can influence the behavior of a precision oscillator? One approach is surprisingly literal: take the experiment one kilometer underground.
Researchers from Quantum Technologies and Dark Matter Labs at the University of Western Australia and their collaborators recently investigated whether cosmic-ray backgrounds may contribute to subtle frequency fluctuations in precision quartz oscillators. Their work compared measurements taken above ground in Melbourne with measurements conducted approximately one kilometer underground at the Stawell Underground Physics Laboratory (SUPL), where the surrounding rock provides a low-background environment shielded from much of the cosmic particle flux.
To conduct an experiment this sensitive, the researchers from QDM Lab needed frequency sources capable of supporting measurements of extremely small fluctuations. Wenzel Associates was proud to support the research by providing the precision oscillators used in the experiment.
The team measured two Wenzel BTULN 10 MHz oven-controlled crystal oscillators (OCXOs). Their signals were combined using a phase-locked-loop measurement system, allowing the researchers to capture the fractional frequency fluctuations of the oscillators over time.
Importantly, the researchers used the same experimental configuration both underground at the CELLAR facility within SUPL and above ground in Melbourne. They also used a portable power supply to keep electrical-noise contributions as similar as possible between the two environments. Following a stabilization period for the oscillator ovens, each measurement collected two hours of data at a 10 kHz sampling rate.
This consistency was critical to the comparison. The Wenzel OCXOs provided a stable precision-frequency platform for examining oscillator behavior across two dramatically different environments.
The two analysis methods revealed an important distinction.
After filtering unwanted harmonic interference, conventional Allan deviation analysis showed no significant difference between the above-ground and underground measurements. However, when the researchers applied multi-scale sample entropy analysis, a difference emerged: at increasing time scales, the underground measurements demonstrated a higher degree of predictability than those recorded above ground.
The researchers are careful not to claim that cosmic-ray muons have been definitively identified as the cause. Further testing, including coincident particle detection and additional environmental controls, would be required to establish that connection. What the experiment did demonstrate was an environment-dependent change in the temporal structure of the Wenzel OCXO frequency fluctuations, one that conventional stability metrics alone did not clearly reveal.
For Wenzel Associates, this collaboration represents exactly the kind of work we are proud to help enable. From precision timing and frequency metrology to emerging experiments in quantum science and fundamental physics, ultra-low-noise frequency sources give researchers the foundation they need to investigate effects at the limits of measurement.
And sometimes, discovering those effects means taking a Wenzel oscillator a kilometer beneath the Earth’s surface. The research team acknowledged that contribution directly in its paper, crediting Wenzel Associates, Inc. for contributing the OCXOs utilized in the work.
For more information about Quantum Technologies and Dark Matter Labs, please visit any of the following.
Website: qdmlab.com
Centre Website: centredarkmatter.org
LinkdIn: ARC Centre of Excellence
Read the full whitepaper to explore the experimental setup, analysis methods, and results in greater detail.
