The nucleus of a thorium-229 atom is like a taut guitar string: it vibrates at a strictly defined frequency. To 'pluck the string', a precise strike is needed — a laser beam of a very specific color. The idea itself dates back to the discovery of radioactivity by Ernest Rutherford and Marie Curie.
Like a guitar body, the microscopic crystalline cavity amplifies the light from the laser many times over, effectively 'rocking' the thorium nuclei. The light flashes they emit are the future 'ticks' of ultra-precise clocks. This approach became possible thanks to methods of laser spectroscopy — the science of light-matter interaction.
Experiments have shown that embedding thorium into the crystal causes acceptable damage. A path towards all-solid-state nuclear clocks on a chip, without vacuum chambers, has been outlined. The development draws on the Standard Model of nuclear physics and photometry to detect light. Such clocks promise a revolution in satellite navigation, quantum computing, and testing fundamental laws.
The excited state of a thorium-229 nucleus lasts almost two hours — an eternity by nuclear standards. This allows its oscillations to be measured with unprecedented precision.
In the novel 'Altered Carbon', interstellar synchronization of consciousness relies on atomic clocks. Nuclear clocks on a chip could bring this fiction closer to reality.