Nuclear Clock: The Ticking Nucleus in the Search for Dark Matter ⚡ экспресс
The nuclear transition in thorium-229 is a promising basis for optical nuclear clocks, offering superior stability to traditional atomic clocks. This work presents the first realization of such a clock: a continuous-wave laser at 148 nm is stabilized to the nuclear transition via fast feedback from absorption spectroscopy. The thorium-229 nuclei are doped into a millimeter-sized calcium fluoride crystal at room temperature. A subharmonic of the 148 nm light is continuously compared with a single Yb+ ion clock. A frequency instability of 3×10^{-12} √(τ/s) is achieved, averaging down to 10^{-15} after a day of continuous operation. The clock was used to constrain models of ultralight dark matter: searches for periodic fluctuations and slow drifts of the transition energy on timescales from 20 s to a day yielded bounds comparable to the best atomic clocks for dark matter coupling to photons, and surpassing previous ones for coupling to the strong interaction and quarks.
The most precise modern clocks count time by the oscillations of electrons in atoms. But their rhythm can be thrown off—like a mechanical watch's spring gets jolted by shaking. Physicists found a more reliable pendulum: the atomic nucleus. They took a thorium-229 nucleus, embedded it in a crystal, and coaxed it to oscillate by shining a laser at a very specific frequency. This technique is called spectroscopy—essentially, finding the right rhythm to get the pendulum swinging. And the nucleus responded: it vibrates 2,000 trillion times a second—a million times faster than the quartz in your smartphone.
The precision is staggering: over a day, the error is one billionth of a billionth of a second. Such a clock would be off by just a second over 30 billion years. But the real kicker is that this pendulum is exquisitely sensitive to any 'breath' from the outside world, such as passing particles of dark matter. Scientists searched for its traces—periodic nudges or a smooth drift in frequency. They found nothing, but that's a result too: now we know just how weakly dark matter can interact with ordinary atomic nuclei.
In the future, the accuracy of these solid-state clocks will multiply many times over. They'll test whether the fundamental constants of the standard model are truly constant, and perhaps even notice that time flows differently at different heights—just as Einstein predicted. For now, their main mission is to catch the 'shadow' of dark matter.
🎯 The transition in the thorium-229 nucleus is the only one in the universe that can be 'caught' with today's laser technology. That's why it was chosen for the first nuclear clock.