Time as a parameter for flow cytometry
Toronto Star, July 10, 2016
Erin Blakemore, The Washington Post
“A clock that could change the way science works”
An obscure element is at core of what may be world’s most precise timepiece, Ytterbium (Yb) isn’t exactly a household name. The element, atomic number 70, is known as the lanthanide series along with neodymium (Nd) and dysprosium (Dy). But ytterbium is at the center of what could be the world’s most advanced atomic clock — a clock so stable, it could one day change the way science itself works. Scientists at the National Institute of Standards and Technology (NIST) in Boulder, Colo., have spent the past several years building a super-precise, cutting-edge clock with ytterbium atoms at its core.
Behind lenses and tangled wires, lies a clock that’s different from the atomic clocks that currently define what the world knows as time. The United States’ current standard-bearers of the second are called NIST-F1 and F-2. Like them, the ytterbium clock measures each second by counting how many times an atom oscillates. But unlike the other clocks, which toss atoms up and measure their emissions as they come back down, the ytterbium clock does its thing with atoms held in place by lasers. Think of the device as a really complicated metronome, driven by Yb atoms that are trapped by an array of lasers cooling them down to just 10millionths of a degree above absolute zero. Once the atoms are held in place, they’re shot with a yellow laser at a specific frequency that excites them. The atoms switch between two energy levels, “ticking” more than 500 trillion times per second.
In the niche world of atomic clocks, stability is the magic word. Because the ytterbium oscillates so quickly and because the clock can trap and analyze thousands of atoms at once, it’s able to reduce errors in how well each tick matches every other tick. “We’ve been able to measure to one part in 1,018,” said Andrew Ludlow, the physicist who leads the ytterbium clock project at NIST. Translation: the error rate of the clock at times approaches one in one quintillion, making it one of the world’s most stable instruments. Since the clock can measure time on such an infinitesimal scale, it could help change the way science works. Clocks such as this are “effectively microscopes into the universe,” Ludlow says, “simply because they measure time so well.”
In the future, quantum physicists may well use the ytterbium clock to measure how well Einstein’s predictions track to the actual ways in which atoms behave — or even help turn the Standard Model of particle physics on its head by proving that dark matter exists, throwing atomic clocks that were once synchronized off-balance by tiny amounts.
“It’s completely speculative, it’s a little bit crazy, but it’s an interesting idea that only the clocks have sensitivity to right now,” says Jeffrey Sherman, a physicist who helped build the clock.
The ytterbium clock could have other applications: forging the way for high-resolution radar, for example, or helping to define a new, more precise standard for the second. But for Sherman, the clock’s real appeal is as much esthetic as it is conceptual.