Scientists have made a major breakthrough that takes us a step closer to developing a nuclear clock — a device that keeps time based on the inner workings of atoms.
For the first time, physicists have used laser light to bump the nucleus of a thorium atom up to a higher energy level. The discovery paves the way for the development of a new clock whose ticks are not only more precise but can probe the most fundamental forces in the universe.
The researchers published their findings April 29 in the journal Physical Review Letters.
“Seeing the first signal was a dream come true,” lead researcher Thorsten Schumm, a professor of quantum metrology at the Vienna University of Technology, told Live Science. “[It’s] the reward for many years of preparation, while also doubting whether this would actually ever work.”
About time
Currently, our most accurate clocks are atomic and keep time by firing lasers at electrons — matching the laser’s frequency with the precise jumps across energy levels it causes electrons orbiting atoms to make. This method gives scientists an ultraprecise measurement of the laser’s frequency, from which they can extract the “tick” of the atomic clock.
However, atomic clocks are far from perfect. The electrons they rely on to keep time sit outside atoms. They are therefore vulnerable to interference from stray magnetic fields or other environmental effects that can subtly alter their energy levels, the frequency of laser light they subsequently respond to, and therefore the time they keep.
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A nuclear clock, on the other hand, would use the energy transitions of nuclei inside the heart of an atom, so they are shielded from outside interference. But many of the gaps between nuclei energy levels are thousands of times greater than those for electrons — meaning they are too large to be crossed with the energy of a laser.
But in the 1970s, scientists found that one isotope, or version, of the element thorium (thorium-229) seemed to have an energy level that could be spanned by laser light.
But finding this precise energy gap has been no simple task. Initially, researchers excited thorium-229 to an energy level far above the two that physicists were actually interested in. They then measured the subtle differences in the energy of light emitted when it…
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