Magnetically-Induced Optical Transparency on a Forbidden Transition in Strontium for Cavity-Enhanced Spectroscopy

TL;DR

This paper demonstrates a novel magnetically-induced optical transparency technique in cold strontium atoms within a high-finesse cavity, enabling narrow, stable spectroscopic features for improved cavity-enhanced spectroscopy.

Contribution

It introduces magnetically-induced optical transparency in a forbidden transition, achieving narrow, cavity-linewidth-independent spectral features in cold strontium atoms.

Findings

Achieved a narrow transmission window approaching atomic linewidth.

Demonstrated immunity to cavity length fluctuations.

Enabled cavity-enhanced spectroscopy with improved stability.

Abstract

In this work we realize a narrow spectroscopic feature using a technique that we refer to as magnetically-induced optical transparency. A cold ensemble of $^{88}$Sr atoms interacts with a single mode of a high-finesse optical cavity via the 7.5kHz linewidth, spin forbidden $^1$S$_0$ to $^3$P$_1$ transition. By applying a magnetic field that shifts two excited state Zeeman levels, we open a transmission window through the cavity where the collective vacuum Rabi splitting due to a single level would create destructive interference for probe transmission. The spectroscopic feature approaches the atomic transition linewidth, which is much narrower than the cavity linewidth, and is highly immune to the reference cavity length fluctuations that limit current state-of-the-art laser frequency stability.