Omar Bustamante/Fusion & NIST

Jun Ye spends most of his days in the basement of a research building at the University of Colorado, Boulder. There, spread across several stainless steel tables, is a nearly half-ton machine that looks a bit like a carnival attraction. It's got lights, wires, and mirrors surrounding a small golden vacuum chamber. Inside the chamber, seven lasers are pointed at a "quilt" made up of 1,000 super-chilled levitating atoms.

This glowing Rube Goldberg-esque contraption is, in fact,¬†a clock. To be precise, it's the most accurate optical atomic clock ever built. According to Ye, it's¬†three times as good as the next most-accurate atomic clock.¬†It's so precise, he says, that if scientists¬†were using it to measure the age of the universe ‚ÄĒ roughly 15 billion years ‚ÄĒ the clock in Ye's office would¬†only be off by about a second.

"It's hard for people to grasp," Ye told me.

The clock, which is described in a paper published today in the journal Nature Communications, builds on the work of dozens of scientists spread across several institutions around the world, going back to the 1980s. Ye has been working on the clock relentlessly for the better part of a decade, showing it off proudly to anyone who comes by: other researchers, representatives from DARPA ( the Defense Department's research wing), even school kids. It's a crowd pleaser. But it's not just a novelty gadget; it's a potential window into the origins of the universe.

Ye's clock.


Optical atomic clocks work by measuring the rate at which the energy level of electrons swirling around an atom's nucleus changes. Accurately measuring that rate of change depends on having a high-quality laser pointed at the atom, measuring its tiny vibrations, and tracking how closely the frequency of light it emits matches up to the frequency at which the clock's atoms oscillate between its low-energy and excited states. The big advancement in Ye's clock is its laser, which is ultra-stable, giving it it the ability to stay synched up its atoms for longer periods of time.

"The progress," said Mikhail Lukin, a quantum physicist at Harvard who wasn't involved in the study, "is amazing. These are now the most precise measurement instruments available to mankind."

Up until recently, the most accurate atomic clocks were based on single trapped positive ions of aluminum or mercury atoms. Ye and his team, though, are working with strontium, the 15th most abundant element on the planet. For decades, strontium was used to produce sugar from sugar beets, and then in cathode ray tubes in televisions. A variant of it has been used in nuclear weapons.


Ye at JILA 2008

Strontium has one huge advantage over aluminum or mercury ions. Its "up" state has a very, very long lifespan, meaning that if the laser is synched up to this excited state, it has a longer period of time during which to measure how many times a strontium atom's electrons go around its nucleus before it falls to its low-energy state. That extended up state gives it more accuracy, when used in an atomic clock. Unlike previous atomic clocks, which used single atoms to measure time, Ye's clock uses a lattice made up of 1,000 strontium atoms.

One other major feat of this new atomic clock is that it works at room temperature. Typically, atomic clocks have been cooled to sub-zero temperatures to avoid having heat radiation change¬†the vibration rates of the atoms inside. But Ye's¬†colleagues developed tiny heat-radiation sensors and stuck them inside the vacuum chamber, to¬†correct for the effects of heat on the strontium atoms. That is yet another breakthrough for the team‚ÄĒand what allows Ye¬†to show the clock¬†off to visitors anytime.


"You can see it in action," he told me. "You can touch it."

The clock doesn't yet have practical, commercial applications, but governments worldwide and companies like Silicon Valley-based quantum-sensor manufacturer AOSense are investing heavily in this field. The hope is that the technology baked into atomic clocks could be used to develop quantum computers and better telecommunications networks in the future. More immediately, since super-accurate atomic clocks can measure changes in the force of gravity at slightly different heights, Ye's clock could enable more precise maps of the Earth and better GPS.

Ye, who's always been intrigued by the relationship of time and quantum mechanics, imagines potential uses that are even more mind-bending. For instance, hyper-accurate atomic clocks could help us tease out some of the mysteries surrounding the origins of the universe by detecting things like gravitational waves, which are ripples in the curvature of spacetime. These waves are thought to burst outward from the epicenter of massive explosions like the Big Bang. Theoretically, gravitational waves interacting with super-sensitive atomic clocks would make them "tick" faster or slower depending on the clock's position relative to them.


"If we can continue to push on its precision and accuracy, it will allow us to peer into the space-time fabric of the universe," Ye told me.

For that to happen, though, the clocks would have to be at least 100 times more accurate than the current cutting-edge versions, he said. That could take years. But this new clock is the closest we've come yet to measuring time in its most exact form.

Daniela Hernandez is a senior writer at Fusion. She likes science, robots, pugs, and coffee.