Electronic Bridge processes in $^{229}$Th-doped LiCAF and LiSAF

TL;DR

This paper investigates electronic bridge mechanisms in thorium-doped crystals to facilitate nuclear excitation, finding laser-assisted schemes significantly outperform spontaneous decay and direct laser excitation, advancing thorium-based nuclear clock development.

Contribution

The study provides a theoretical analysis of electronic bridge processes in thorium-doped crystals, highlighting the potential of laser-assisted schemes for nuclear excitation in thorium-based clocks.

Findings

Laser-assisted electronic bridge schemes are more efficient than spontaneous decay.

Spontaneous electronic bridge rates are very small.

Laser schemes offer promising prospects for nuclear clock operation.

Abstract

Electronic bridge mechanisms driving the $^{229}$Th nuclear clock transition in the vacuum-ultraviolet-transparent crystals $^{229}$Th:LiCAF (LiCaAlF$_6$) and $^{229}$Th:LiSAF (LiSrAlF$_6$) are investigated theoretically. Due to doping-induced symmetry breaking within the host crystal, electronic defect states emerge around the thorium nucleus and can facilitate nuclear (de)excitation via laser-assisted electronic bridge mechanisms. We investigate spontaneous and laser-assisted electronic bridge schemes for different charge compensation mechanisms. While the calculated spontaneous electronic bridge rates are very small, laser-assisted electronic bridge schemes for nuclear (de)excitation turn out to be significantly more efficient than both spontaneous nuclear decay and direct laser excitation, offering promising prospects for the future clock operation.