Magnetic Resonance Linewidth of Alkali-Metal Vapor in Unresolved Zeeman Resonance Regime

TL;DR

This paper develops a theoretical model to understand the magnetic resonance linewidth of alkali-metal vapor in the unresolved Zeeman resonance regime, revealing the conditions for light-narrowing and the influence of quantum coherence on linewidth.

Contribution

It introduces a new theoretical framework for analyzing linewidth in the unresolved Zeeman regime, focusing on quantum coherence effects and the spin exchange to destruction rate ratio.

Findings

Light-narrowing occurs only above a critical spin exchange to destruction rate ratio.

Quantum coherence coupling significantly affects the linewidth.

The model aids in optimizing atomic magnetometer performance.

Abstract

The study of magnetic resonance linewidth is crucial in magnetic resonance physics and its applications. Previous studies focused on the linewidth of alkali metal atoms within the spin-exchange relaxation-free regime near zero magnetic field and in strong magnetic fields where Zeeman resonances are well resolved due to the quadratic Zeeman effect. However, the linewidth in the unresolved Zeeman resonance regime, which is prevalent in various magnetometer and comagnetometer applications, is not well understood. To address this, we developed a theoretical framework based on the master equation for alkali metal atoms and solved it under the rotating wave approximation and weak driving conditions. Our numerical calculations and analytical expressions reveal that the light-narrowing effect occurs only when the ratio of the spin exchange rate to the spin destruction rate exceeds a critical value. Additionally, we show that the linewidth in the unresolved Zeeman resonance regime is significantly influenced by the mutual coupling of quantum coherence between different Zeeman sublevels. These findings provide a theoretical tool for understanding spin relaxation in alkali-metal atoms and optimizing the performance of atomic magnetometers and comagnetometers operating in this regime.