The Physicist Building the World’s Most Precise Clock

We take clocks for granted. In the modern world, time is calculated everywhere we look. If there’s not a watch on your wrist, there’s one on your phone. Most modern computers keep track of the time in the corner of the screen. Appliances from coffee makers to microwaves have a digital readout of the time.

The measurement of time is ubiquitous, inescapable, and incredibly important. “[The clock] has played an important role in human history,” Jun Ye—who is Adjoint Professor of Physics at the University of Colorado, and a researcher into precision measurement—told me over the phone. “It helped build a more technically advanced society.”

Ye and his team of researchers want to push the limits of human understanding. They want humanity to explore the stars, explain dark matter and dark energy, and find the connections between quantum physics and gravitational physics. Ye thinks that perfecting the clock could be an important step towards achieving those goals.

His team has built an atomic clock that will keep an accurate reading of time for billions of years. This optical lattice clock generates a grid of lasers that creates impressions in a flat surface where atoms rest. Then other lasers fire at the atoms to excite them and their various frequencies help create an accurate measure of time. Readers can find a more in-depth and technical explanation of the clock here.

Building the atomic clock has been decades in the making. The project started just after World War II when, according to Ye, scientists realized that major advances in timekeeping preceded major advances in technology. The mechanical clock and quartz crystal clark helped spur on the industrial revolution, for example, by creating a demand for timepieces that drove innovations in manufacturing.

“After World War II, people started to realize that the atom [was] the quantum standard,” Ye said. “If you can read the information from each individual atom, how the electrons are moving around the nucleus and how the electrons are caught up in their spin, then that would be the best time piece…for an industrialized society.”

The original atomic clocks, built in the 1950s, used microwaves to manipulate the atoms and recorded an electron’s orbit around the nucleus of an atom as the clock’s pendulum. After the discovery of frequency combs and cold atoms, scientists realized they could make a more accurate and precise clock.

“If you move the frequency into the visible light range…the oscillation of the frequency is much much higher than the frequency of the microwave,” Ye said.

According to Ye, a regular pendulum updates once per second. A microwave atomic clock updates around 10 billion times per second. His team’s optical lattice clock updates one million billion times per second. “If something is updating faster, it allows you to make a more precise measurement,” he said.

That precision is important. Ye told me it will do so much more than just give us an accurate reading of the time of day. “It’s a key piece of technology that allows us to navigate on Earth as well as, in the future, navigate to Mars and beyond our solar system,” he said.

Beyond spaceflight, Ye believes the his team’s atomic clocks will be a window into exploring the mysteries of the universe. We tend to forget that space and time are connected. In a very basic way, gravity warps time. Ye thinks that one day clocks will be so accurate that a measurement of time may be able to tell us something about gravity's effect on time.

“If we continue to make a clock very accurate based on atoms, one day, we will be able to make a clock so accurate that the individual movement of an atom [is] in a field where quantum physics is the governing dynamic,” he said.

Ye conceded that Earth-based experiments will always experience some level of space-time curvature because of the planet’s gravity. “If we can start to explore this connection directly—between quantum physics and gravitational actors—we will be exploring something completely new. There are many unknowns in the universe [like] dark matter and dark energy. A clock might be the technology that allows us to explore that.”

Ye pointed to Einstein’s theory of general relativity, noting his observation of the connection between space and time. “When you have a heavy object, you curve space-time fabric,” Ye said. “What else can be a better tool to go in there and explore this than a device that’s built so precisely and accurately that it is able to measure that? Combining, really, quantum physics [and] gravitational physics…into a single device.”

For a concrete example of how this might work, Ye imagined a future where atomic lattice clocks positioned around the Earth measured tiny and precise fluctuations of gravity on the Earth’s surface. “Maybe we…put a bank of clocks around an active volcano and..predict if mass is moving underneath,” he said. “We can actually make a prediction based on how the time is slowing down and speeding up due to the mass motion. We can build a clock network as a geological sensor.”

Beyond the clock-based applications are all the technological advances that result from creating such a device. Precise clocks need stable lasers and other advanced technologies that will have additional benefits for the world. “It turns out these lasers can be used to watch chemical reactions in our atmosphere,” Ye said. “We can use those lasers to monitor people’s breath to see if someone’s sick. Who’d have thought that when we started the optical clock research, that we’d have a laser that could smell people’s breath? That’s something unexpected that’s a big part of what we do.”

Ye also told me that the extreme precision required for the atomic clock will push forward the world of quantum computing. “We have the technology…to manipulate individual atoms or individual ions…so we can build a quantum…system where computation can grow and grow exponentially fast,” he said. “You can do calculations in parallel that require very precise control of various particles, even to the point of being able to control mini-particles at quantum states.”

It may seem ridiculous that a clock could tell us so much about our universe and push the boundaries, but Ye told me to remember the sundial. “The sundial was a very simple device that allowed you to know, based on the position of the sun overheard, where you are, what time it is during the day,” he said. “Using that, you can tell the four seasons. You can tell how the Earth is rotating around the sun. It’s the same way with the atomic clock, but it’s probing a much deeper and more precise order of our universe.”

It’s that meticulous exploration of the universe that intrigues and delights Ye. “Some educated people going through college say, ‘We’ve heard of general relativity. We know time is different at different elevations,’” he said. “But…if you can tell them one day we will be able to make a device so precise that a little minute motion of atoms can actually experience different times, that would be mind boggling.”

“We know that our understanding of the physical world based on our standard model is not complete,” Ye added. “We know there are mysteries out there we can not explain… yet. You just have to keep building the most sensitive device that allows you to explore things that haven’t been explored.”

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