As the world considers redefining the precise length of a second, Singapore’s Centre for Quantum Technologies has delivered a new contender for the ultimate master timekeeper.
Tests of their new lutetium-based atomic clock reveal it not only tick-tocks at a rate that makes it comparable to existing technology, but potentially even surpasses it.
“I am confident that what we have now is the most accurate clock in the world,” says National University of Singapore physicist Murray Barrett.
Atomic optical clocks keep time by using electrons as a pendulum. Just as the swinging weight inside a grandfather clock moves in a precise pattern, an electron pushed with a precise amount of energy will “swing” between quantum states at a reliable frequency.
Atoms of different elements will keep slightly different times, of course. Since the 1960s, cesium has been the element of choice, though clocks based on other metals, such as ytterbium or strontium, have been created for their own handy attributes.
One desirable characteristic in an atomic clock is a low systematic uncertainty. Every process requires balancing sensitivity with reliability, ensuring electrons respond to the push of a laser’s pulse and then emit a tell-tale blip of light without fail.
Lutetium is a heavyweight as far as other elements in atomic optical clocks go. With an atomic mass of 71, it sits at the end of the lanthanide series, just past ytterbium, making it less likely to wobble. It also barely reacts to thermal radiation or shifts in magnetic fields, leaving less room for environmental errors to creep in.
It also hums at a rate of around 10,000 times that of cesium, potentially making for a highly accurate and highly reliable material to measure time at the finest of scales.
“The good properties mean that high accuracy can be achieved even in a wide range of environments,” says Barrett. “The lutetium clock would be stable even if you went from the hottest place recorded on Earth in Death Valley to the coldest place in the Antarctic plateau.”
Unfortunately, it is also the rarest of all Earth’s rare earth elements, and happens to be one of the least studied as far as its time-keeping properties are concerned.
That lack of knowledge is something Barrett and his team have been working on over the past decade. Now, they finally have the results they’ve been anticipating.
The team scrutinized their work by comparing a pair of lutetium clocks under conditions informed by strict criteria. Years of experiments on both the system and the charged lutetium atom allowed them to cut down the level of uncertainty to a degree that put their clock among the best of the best.
Earlier this year, Chinese Academy of Sciences researchers achieved a systematic uncertainty of 4.4 x 10-19 using a setup based on calcium ions.
Comparisons between the two lutetium clocks delivered a systematic uncertainty of just 1.2 x 10-19, a number that may be improved upon further with more measurements.
It’s hard to emphasize just how fiddly this kind of work is. Gravity’s distortions on time are obvious across just a handful of millimeters when seconds are being divided into trillionths, meaning even a near-imperceptible difference in the distances from Earth’s core could create a degree of disagreement between the two clocks.
Nonetheless, it’s this very sensitivity that makes them so incredibly useful. Only with this level of precision can we hope to devise experiments that could one day resolve the nagging conflict between general relativity’s seamless concept of gravity and the granularity of reality implied by quantum mechanics.
In the meantime, there is also the question of just how precise we ought to make the fundamental unit of time, the second. Right now, it is 9,192,631,770 hyperfine jumps of an electron being nudged by microwaves in an atom of cesium-133 in its ground state.
Could lutetium do a better job?
“In the future, I just don’t see how this clock can be beat,” says Barrett.
This research was published in Nature.
Source: National University of Singapore
