Atomic clocks are the world’s gold standard for timekeeping, at the heart of everything from GPS navigation to synchronised networks. A ytterbium atomic clock is so precise it misses one second every 23 billion years.
In two papers in Nature , scientists from Europe and China have now reported the world’s first working nuclear clocks. Yet scientists are interested in more precise clocks to detect infinitesimal changes in fundamental forces and further advance navigation. While, in an atomic clock, an atom’s electrons are easily disturbed by electric or magnetic fields and temperature changes in a room, the nucleus is shielded by the electron cloud.
The laser’s frequency can drift slightly, however. If it happens less often than expected, the laser’s frequency has drifted away and a computer corrects it. A feedback loop constantly checked the laser against the thorium nuclei and corrected it. These prototypes are not yet as precise as the best atomic clocks but their architecture is proven. With upgrades to laser power and crystal quality, scientists expect nuclear clocks to eventually surpass their atomic predecessors.
Because the clock operated within a simple crystal, it could pave the way for compact, portable clocks. In a nuclear clock, scientists expose thorium-229 nuclei to the laser and check how readily they become excited. In one study, teams from Beijing and Shanghai embedded thorium-229 in calcium fluoride crystals and fired an ultraviolet laser at them.
