Hyperfine spectroscopy of optical-cycling transitions in singly ionized thulium

TL;DR

This study provides a comprehensive spectroscopic analysis of singly ionized thulium, establishing its suitability for quantum applications through detailed transition characterization and hyperfine structure measurements.

Contribution

It offers the first complete spectroscopic roadmap for optical cycling in Tm+ ions, including hyperfine constants and metastable state characterization for quantum use.

Findings

Identified key optical cycling transitions at 313 nm and 448/453 nm.

Determined hyperfine A constants for relevant energy levels.

Measured lifetime and hyperfine structure of a metastable state.

Abstract

We present a spectroscopic investigation of $^{169}\mathrm{Tm}^+$ that provides two key foundations for its use as a platform for advanced quantum applications. First, we establish the complete spectroscopic road map for optical cycling (including laser cooling) by performing high-resolution spectroscopy on $^{169}\mathrm{Tm}^+$ ions in an ion trap. We characterize the primary $313\,\mathrm{nm}$ and complementary $448/453\,\mathrm{nm}$ cycling transitions, identify the essential near-infrared repumping frequencies, and determine the magnetic-dipole hyperfine $A$ constants for all relevant levels. Second, we report a detailed characterization of a metastable state as a candidate for hosting a robust qubit, performing lifetime measurements and Zeeman-resolved microwave hyperfine spectroscopy with $\mathrm{kHz}$ precision.