New Optical Atomic Clock Has Heart Smaller Than a Coffee Bean

The clock's atom chamber is a mere 3 millimeters across mounted on a silicon chip
Loukia Papadopoulos

Optical clocks are types of atomic clocks that keep time more reliably by using light tuned to rubidium atoms. This allows them to beat trillions of times per second.

A heart smaller than the size of a coffee bean

Now, researchers have engineered an optical clock with a heart smaller than the size of a coffee bean. The new clock uses an atom chamber a mere 3 millimeters across mounted on a silicon chip.


This is a vast difference from the chamber of atoms at the heart of optical clocks that used to run a meter across. The clock also features a “pendulum” that is a laser tuned to about 385.285 terahertz.

What that means is that its light undulates 385.285 trillion times per second. That's too fast for modern electronics to count so the optical clock uses two components called frequency combs.

Mounted on tiny chips, these combs translate the laser’s high-frequency optical ticks into slower, widely-used, countable ticks. The optical clock ultimately produced ticks paced at 22 gigahertz, 50 times better than the current cesium-based chip-scale clocks. 

Remarkable accuracy

"Laboratory optical atomic clocks achieve remarkable accuracy (now counted to 18 digits or more), opening possibilities for exploring fundamental physics and enabling new measurements. However, their size and the use of bulk components prevent them from being more widely adopted in applications that require precision timing," write the researchers in their new paper

But before you get too excited, envisioning an extremely efficient pocket watch, it should be noted that the clock is hooked up to supporting electronics that fill two tables. The new clock might be tiny compared with its predecessors, but it still has a long way to go.

Still, its new chip-based heart requires very little power (just 275 milliwatts) and, with additional advances, could potentially be made small enough to be handheld. "These results demonstrate key concepts of how to use silicon-chip devices in future portable and ultraprecise optical clocks," write the researchers.

“We made an optical atomic clock in which all key components are microfabricated and work together to produce an exceptionally stable output,” NIST Fellow John Kitching said. “Ultimately, we expect this work to lead to small, low-power clocks that are exceptionally stable and will bring a new generation of accurate timing to portable, battery-operated devices.”  

The study is published in Optica.

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