Crystal Fields and Zeeman Effect for Thulium in Solid Argon

TL;DR

This study investigates the optical and magnetic properties of thulium atoms in solid argon, revealing narrow spectral lines, crystal field effects, and the potential for all-optical magnetic field sensing at the nanoscale.

Contribution

It provides high-resolution spectroscopy data and identifies crystal field levels and Zeeman effects in thulium-doped solid argon, advancing understanding for quantum sensing applications.

Findings

Narrow ensemble linewidths at 1140 nm transition

Crystal field effects are nearly axial in two trapping sites

Zeeman shifts enable polarized spectroscopy for magnetic sensing

Abstract

Optically active defects suspended in an inert solid are an interesting system for sensing and magnetometry at the nanometer scale, in addition to being a potential source of high-density, identical quantum emitters for quantum information. Beyond their response to external fields, the optical absorption and emission spectra also reflect information about the host matrix, which is critical to understand for either application. For the particular system of thulium atoms implanted in solid argon, high resolution laser spectroscopy reveals narrow ensemble linewidths of the 1140 nm f to f ground state spin-orbit transition, which is split due to crystal field effects and hyperfine coupling. Pump-probe spectroscopy is used to identify crystal field levels in at least two stable trapping sites, and the crystal field is determined to be nearly axial in both sites. Strong selection rules indicate that this transition becomes magnetic-electric in the argon host, most likely due to dielectric effects. In the presence of mT magnetic fields, Zeeman shifts are resolvable by laser fluorescence, allowing crystal axis selective polarized spectroscopy. These results show that all-optical detection schemes for DC magnetic fields are already possible with thulium-doped argon, and point towards more informed strategies for monitoring and improving crystal growth and annealing.