There are many ways we can keep track of passing seconds. Counting “Mississippi” between numbers works. Monitoring the swing of a pendulum is a little more accurate. Or if you want to get super fancy, use the piezoelectric buzz of electrified quartz.
Now we can use the high-frequency hum of thorium-229 and potentially set a record in timekeeping precision.
Two research teams have independently delivered working versions of a radical new kind of timekeeping device based on the jitter of an atom’s nucleus, realizing a goal decades in the making.
At their core, all clocks do the same thing – divide time into increments separated by the same duration. More increments crammed into every second means more precision.
For more than three-quarters of a century, atomic clocks have been the gold standard for counting the moments, tick-tocking at a frequency set by electrons transitioning between orbitals in a caesium atom.
Electrons aren’t the only parts of an atom capable of swinging back and forth in a predictable pattern. The nucleus itself can jiggle. What’s more, it can do so under much higher energies than electrons, potentially squeezing in more swings per second.
In 2003, researchers realized that the hypothesized “nuclear transition” of a thorium isotope could be practically achieved at a frequency modern lasers could deliver.
It took 13 years for researchers to observe the phenomenon, and a further 12 to experimentally work out the precise wavelength of UV radiation needed to turn it into an atomic timepiece.
The final hurdle was to develop a method for reliably transmitting light in a part of the spectrum that’s easily absorbed by atmospheric gases.
Now two experiments – one led by quantum metrologist Luca Toscani De Col from the Vienna Center for Quantum Science and Technology, the other led by Tsinghua University physicist Beichen Huang – have cracked the problem, encasing thorium-229 nuclei in calcium fluoride.
To mitigate remaining obstacles, Huang’s team cranked up the UV laser, while Toscani De Col’s colleagues increased concentrations of the isotope.
Both resulted in a practical nuclear clock that could, in theory, lead to more precise forms of timekeeping. The latest clocks are capable of measuring time to an incredible 19 decimal places, a figure that nuclear clocks are theorized to surpass.
Reliably chopping time up into ever finer units gives researchers better tools for measuring near-imperceptible changes that gravity and acceleration exert on spacetime, allowing them to test relativity’s predictions or search for gaps in the Standard Model.
Just to put their new tool through the wringer, Toscani De Col and his team used it in a search for signs of low-mass dark matter. Had they found it, they would have solved a vexing problem in physics that has failed to explain the nature of 85% of the Universe’s mass.
In any case, it sure beats counting in Mississippis.
Both studies are available on the pre-publish server arxiv, here and here.
Source: Phys.org
Fact-checked by Bronwyn Thompson
