AsianScientist (May 21, 2018) – In a study published in Nature Communications, a research group in Singapore has singled out an atom that could allow us to build better atomic clocks.
Atomic clocks have set the global standard for measuring time for over half a century. But since the second was defined with reference to cesium atoms in the 1960s, there has been worldwide competition to improve the accuracy and stability of atomic clocks.
Time signals from cesium clocks still support the Global Positioning System and help to synchronize transport and communication networks, but atoms of many other species, such as ytterbium, aluminum and strontium, now vie to make the most precise measurements of time. These new-generation clocks, with uncertainties around one part in a billion billion, are proving their mettle in testing fundamental physics—from measurements of gravity to looking for drifts in fundamental constants.
In the present study, researchers at the Centre for Quantum Technologies at the National University of Singapore (NUS) found that a previously neglected element—lutetium (Lu)—could improve on today’s best clocks. Lu is a rare earth element with atomic number 71.
“The ultimate performance of a clock comes down to the properties of the atom—how insensitive the atom is to its environment. I would call Lu top in its class,” said Associate Professor Murray Barrett of NUS who led the research.
The ‘tick’ of an atomic clock comes not directly from the atom, but from the oscillation of a light wave. The oscillation frequency is fixed by locking it to the resonant frequency of the atom.
In practice, this means a laser is tuned to make one of the atom’s electrons leap from a low energy level to a higher energy level. How much energy this jump takes is a fixed property of the atom. The laser’s frequency is matched to deliver just the right amount of energy in a single light particle (a photon). Once this sweet spot is found, the clock counts time by measuring the oscillations of the light wave.
Cesium clocks run at microwave frequency—or exactly 9,192,631,770 ticks per second. The most recent generation of atomic clocks run at optical frequencies, which tick some ten thousand times faster. Counting time in smaller increments allows for more precise measurement.
But there’s more to making good clocks than a quick tick: that tick also needs to be stable over time. One source of inaccuracy in the clock frequency is sensitivity to the temperature of the environment surrounding the atom. This is where Lu may shine. The researchers showed that Lu had a lower sensitivity to temperature than atoms used in clocks today. These measurements add to earlier results showing Lu could make a high-performance clock.
The team is not aware of any other groups working with Lu. One reason Lu was untried is that it required a new technique, discovered by Barrett and his collaborators, to cancel sources of inaccuracy in the clock. This ‘hyperfine averaging technique’ is described in earlier papers.
“I don’t see it as being an overly technical, difficult thing to do, but I think people are waiting to see how this works out,” said Barrett.
The article can be found at: Arnold et al. (2018) Blackbody Radiation Shift Assessment for a Lutetium Ion Clock.
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Source: National University of Singapore.
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