Deep inside the atomic nucleus of thorium-229, there's a stiff lever. To flip it from one position to another, you need to apply force, and that usually takes time. This isotope has two very close energy levels, and the transition between them can be triggered by a laser pulse. But if you act too roughly, the lever might slip, and if you're too cautious, the process drags on forever.
Until recently, physicists used a method of smooth redirection. They slowly moved the lever, gradually shifting the fulcrum. It worked, but it took hundreds of milliseconds — an eternity for nuclear processes. In the new work, the authors found a shortcut: they added an extra laser pulse that acts like a sharp nudge at just the right moment. This approach allowed them to switch the nuclear state of thorium-229 in just hundreds of microseconds, with nearly 80% success.
This result is important for building ultra-precise nuclear clocks, which would be tens of times more stable than today's atomic clocks. Moreover, manipulating nuclear states opens the door to studying subtle effects of electron-shell–nucleus interactions — an area still full of mysteries. Perhaps in the future, such methods could even allow us to control radioactive decay.
Now that the lever inside the nucleus can be controlled quickly and precisely, physicists have a doorway to new discoveries.
The energy of the isomeric transition in thorium-229 is about 8.3 electronvolts — a million times smaller than typical nuclear transitions, so it can be excited with an ordinary ultraviolet laser.
In Peter Watts's novel Blindsight, alien ships use exotic nuclear transitions for communication — maybe thorium-229 would be a first step toward such technology.