Time can feel like it’s slipping away in a blink or stretching on for an eternity. Despite how imprecise time might feel, the clock on your phone or computer ticks to a very precise rhythm thanks to atomic clocks—ones that measure time by the gentle, steady pulse of atoms.
But now researchers are stepping into a new era of timekeeping with nuclear clocks—clocks that run off the signal from the core of an atom rather than the signal from the electrons surrounding that core. Instead of losing a second over tens of millions of years, as atomic clocks do, a nuclear clock would barely lose a second over billions of years.
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In a paper published Wednesday in the journal Nature, scientists from JILA (formerly the Joint Institute for Laboratory Astrophysics) and laser company IMRA in the US, as well as physicists from the Vienna Center for Quantum Science and Technology, demonstrate the basic elements needed for such a clock.
Atomic clocks tick when the electrons that orbit the nucleus of an atom, like planets orbiting the sun, jump between orbits and give off or absorb a tiny bit of radiation. Nuclear clocks are similar but would measure the tiny jumps of parts inside the nucleus.
To make the jumps happen, scientists need to jolt the nucleus with exactly the right amount of energy. For most nuclei, that’s a fairly large amount. In this latest paper, researchers used atoms of a silver-olive-gray metal called thorium 229 because it doesn’t need to be bombarded with as much energy to achieve these jumps.
“The thorium nucleus is very special,” explained Jun Ye, a physics professor at JILA and the National Institute of Standards and Technology. An ultraviolet laser in a vacuum gave the nucleus the kick it needed to “tick.”
But, getting the nucleus to produce its time signal was only half the battle. Researchers still needed a device to actually read the clock. Enter the optical frequency comb—a kind of time ruler made of laser light that very precisely measures the frequency of the ticking nucleus (aka the ticking). Ye helped invent this ruler more than 20 years ago.
The concept of nuclear clocks isn’t new, explained Ye. They were actually first proposed in the 1970s, but it took decades to get to the point where scientists could actually make and test the elements needed for one. One key breakthrough came just earlier this year, when researchers discovered the narrow window of energy needed to make the thorium 229 nucleus tick.
“This really has taken decades to develop. Finally this all came together in the paper that we published in Nature,” Ye said. Their experiment is essentially a lab demonstration, rather than a fully functioning clock, but that doesn’t mean its significance should be underestimated. “All the pieces are there,” said Ye.
As a final step, Ye’s team compared the ticking of their prototype nuclear clock with the ticking of the world’s most accurate atomic clocks (which Ye also helped develop). “This is the first time a very precise measurement of the nucleus has been made and the frequency is directly connected to an atomic clock,” Ye said. This showed them the nuclear clock ticked relative to today’s time-standard, therefore paving the way for nuclear clocks to become the way all clocks around the world are set.
Syncing the world’s clocks to this new, more precise, standard could mean more precise navigation systems or faster internet, by making it faster to sync all computer times around the world to the standard. Also, because the nucleus is essentially shielded within the atom, it’s less likely to be disturbed by environmental forces and could make for more robust, secure, and reliable timekeeping.
In a pure science sense, nuclear clocks could even help probe the mysteries of the universe including dark matter. To do that, Ye explains, you’d compare two ticking nuclear clocks and see if one was interacting with the mysterious substance and therefore altering its tick almost imperceptibly. “We’re pushing the precision [of clocks] to such a level that we can detect the presence of dark matter. The likelihood of seeing it is becoming greater.”
But we aren’t there yet. This latest research essentially developed a prototype nuclear clock. “Unless something is running 24/7, it’s not really a clock,” Ye said. “To turn this into a clock you need a laser that’s running all the time.”
