Frequency-Axis Calibration via Autler-Townes Splitting in an Electromagnetically Induced Transparency Feature

Abstract

Rydberg atom-based electrometry is a pivotal technology that enables radio-frequency (rf) field measurements traceable to the International System of Units. This is typically accomplished by converting the direct rf power measurement of classical probes to a frequency measurement referenced to two well-defined spectral features, a commercial wavemeter, or narrow cavity lines produced via clock disciplined electro-optic modulators, although there exist cases where none of these are available. In this article, we demonstrate that a known rf frequency scale can be used to infer a laser's frequency scan using Autler-Townes (AT) splitting. In other words, we show that frequency-axis calibration can be achieved using the avoided-crossing behavior of near-resonant rf radiation. The relative separation between AT-split features is measured as a function of an applied rf field's power and detuning from atomic resonance. These peak separations are then fit to a simple, two-level model using a weighted nonlinear least-squares regression analysis that utilizes three fitting parameters, one of which is the desired calibration factor. While we do not benchmark this method against an absolute frequency reference, we do show that this method is (1) consistent with calibration via known fine-structure separation to within approximately 1.11% or better, and (2) robust against substantial experimental deviation from the system's known rf power dependence.