Direct detection of the 229Th nuclear clock transition

TL;DR

This paper reports the direct detection of the $^{229}$Th nuclear isomer, confirming its existence and providing energy and half-life estimates, which are crucial steps toward developing a nuclear clock that could surpass current atomic clocks.

Contribution

The study provides the first direct detection of the $^{229}$Th nuclear isomer, establishing foundational data for future nuclear clock development.

Findings

Isomeric energy constrained between 6.3 and 18.3 eV

Half-life longer than 60 seconds for $^{229m}$Th$^{2+}$

Confirmation of the isomer's existence

Abstract

Today's most precise time and frequency measurements are performed with optical atomic clocks. However, it has been proposed that they could potentially be outperformed by a nuclear clock, which employs a nuclear transition instead of the atomic shell transitions used so far. By today there is only one nuclear state known which could serve for a nuclear clock using currently available technology, which is the isomeric first excited state in $^{229}$Th. Here we report the direct detection of this nuclear state, which is a further confirmation of the isomer's existence and lays the foundation for precise studies of the isomer's decay parameters. Based on this direct detection the isomeric energy is constrained to lie between 6.3 and 18.3 eV, and the half-life is found to be longer than 60 s for $^{229\mathrm{m}}$Th$^{2+}$. More precise determinations appear in reach and will pave the way for the development of a nuclear frequency standard.