Measurement of the lowest millimetre-wave transition frequency of the CH radical

TL;DR

This paper reports a highly precise laboratory measurement of the lowest millimetre-wave transition frequency of the CH radical, crucial for testing variations in fundamental constants across the universe.

Contribution

The study provides the most accurate laboratory frequency measurement of CH's lowest millimetre-wave transition, significantly reducing previous uncertainties.

Findings

Frequency measured with 0.6 kHz accuracy

Uncertainty reduced by two orders of magnitude

Enables more sensitive tests of fundamental constant variations

Abstract

The CH radical offers a sensitive way to test the hypothesis that fundamental constants measured on earth may differ from those observed in other parts of the universe. The starting point for such a comparison is to have accurate laboratory frequencies. Here we measure the frequency of the lowest millimetre-wave transition of CH, near 535 GHz, with an accuracy of 0.6 kHz. This improves the uncertainty by roughly two orders of magnitude over previous determinations and opens the way for sensitive new tests of varying constants.