# The concept of laser-based conversion electron M\"ossbauer spectroscopy for a precise energy determination of $^{229m}$Th

## TL;DR

This paper proposes a laser-based method using thorium atoms for precise measurement of the $^{229m}$Th nuclear isomer energy, potentially enabling nuclear laser spectroscopy and a nuclear optical clock.

## Contribution

It introduces a novel nuclear laser excitation scheme with thorium atoms, significantly improving energy resolution and facilitating the development of a single-ion nuclear optical clock.

## Key findings

- Potential to determine the isomeric energy to 40 μeV resolution
- Achieves a 10,000-fold improvement over current energy constraints
- Enables nuclear laser spectroscopy of individual thorium ions

## Abstract

$^{229}$Th is the only nucleus currently under investigation for the development of a nuclear optical clock (NOC) of ultra-high accuracy. The insufficient knowledge of the first nuclear excitation energy of $^{229}$Th has so far hindered direct nuclear laser spectroscopy of thorium ions and thus the development of a NOC. Here, a nuclear laser excitation scheme is detailed, which makes use of thorium atoms instead of ions. This concept, besides potentially leading to the first nuclear laser spectroscopy, would determine the isomeric energy to 40 $\mu$eV resolution, corresponding to 10 GHz, which is a $10^4$ times improvement compared to the current best energy constraint. This would determine the nuclear isomeric energy to a sufficient accuracy to allow for nuclear laser spectroscopy of individual thorium ions in a Paul trap and thus the development of a single-ion nuclear optical clock.