Impact of Heavy Noble Gases on the Magnetic Resonance Linewidth of Alkali-Metal Atoms: A Theoretical Study

TL;DR

This theoretical study analyzes how heavy noble gases, especially xenon, influence the magnetic resonance linewidth of alkali-metal atoms in NMR gyroscopes, revealing key collisional mechanisms and optimization strategies.

Contribution

We develop a density matrix-based theoretical framework to quantify xenon-induced collisional effects on alkali-metal resonance linewidths under realistic conditions.

Findings

Xenon broadens linewidth mainly through binary collisions and vdW-mediated processes.

Nitrogen buffer gas can both relax spins and modulate collision rates, affecting linewidth.

A temperature threshold for light-narrowing depends on xenon density.

Abstract

Nuclear magnetic resonance gyroscopes (NMRGs) employ noble-gas nuclear spins as inertial sensors and alkali-metal atoms as in-situ magnetometers. Heavy noble gases, particularly xenon, are widely used due to their large nuclear spin and strong spin-exchange coupling with alkali-metal atoms. However, their presence introduces additional collisional mechanisms that affect the alkali-metal magnetic resonance linewidth, thereby influencing magnetometer sensitivity and overall gyro performance. In this work, we develop a theoretical framework based on the density matrix formalism and master equation approach to quantitatively study how xenon-induced two-body and three-body interactions modify the linewidth of alkali-metal atoms under realistic NMRG conditions. Our analysis reveals that Xe atoms primarily broaden the linewidth via binary spindestruction collisions and van der Waals (vdW)-mediated F-damping processes, while the effect of Xe nuclear polarization is negligible at the ~1% level. We further demonstrate that nitrogen buffer gas plays a dual role: it directly contributes to alkali-metal spin relaxation through binary collisions and indirectly modulates vdW collision rates by altering molecular lifetimes. The interplay between these processes leads to an optimal nitrogen density that minimizes the linewidth. Additionally, we identify a temperature threshold above which light-narrowing emerges, with this threshold increasing alongside Xe density. These findings provide theoretical insight for optimizing spin relaxation control in alkali-metal magnetometers and improving NMRG performance.