Towards a 229Th3+ Nuclear Clock

Atomic clocks are the most precise instruments in existence, with current state of the art clocks achieving fractional uncertainties at the level of $5.5\times10^{-19}$. This precision places atomic clocks in a position to test the very fundamental postulates of modern physics that are encoded in all those digits. To distill information from them, different atomic systems with their unique properties have to be compared; this is where 229-thorium (Th) stands out. Because the low-lying isomeric state is the result of a near-degeneracy between the strong and electromagnetic forces, the $^{229}$Th isomer transition is highly sensitive to changes in either. This makes it an excellent probe for searching for variations in the fine structure constant $\alpha$ as well as the strong interaction scale parameter (ratio of the quark mass to the QCD scale parameter, $m_q/\Lambda _{QCD}$). In addition, it is far less sensitive to external fields owing to the nucleus' small size and tight binding energy, making it a promising candidate for a next-generation clock with a sub-$10^{-19}$ inaccuracy. Here, we present our efforts on building such a next-generation clock based on driving the isomer transition via an electron-bridge process in $^{229}$Th$^{3+}$ ions trapped in a Paul trap.