“Knowing the energy of this transition to within one electron volt is of little use, if you have to hit the right energy with a precision of one millionth of an electron volt in order to detect the transition.”
Physicists have speculated since the 1970s that thorium-229 has a nuclear transition a laser could flip. Thorsten Schumm’s team at TU Wien and PTB finally hit it on November 21, 2023, after he spent his research career on it since 2009. The trick was crystals holding about ten to the seventeenth thorium nuclei, so one laser shot hits them all at once. The payoff is a nuclear clock, which is still a goal and not a product.