The quest for measuring time more accurately has produced some of the most captivating advances in physics and engineering. Optical lattice clocks now drive this endeavor—machines so precise they’d lose only one second over hundreds of billions of years. Recent advances aren’t merely setting new records for precision; they’re opening up new opportunities in science and technology as well.
Learning How Optical Lattice Clocks Work
These timepieces are founded on an amazingly simple principle. Individual atoms of an element, cooled to near absolute zero, act like nature’s most consistent metronomes. When electrons in them move between energy levels, they emit or absorb light at a frequency identical for every atom of the same kind. Using lasers tuned to this frequency, scientists can quantify time with mind-boggling precision. These atoms are immobilized within an optical lattice of light, restricting movement and maintaining interference from the surroundings at a low level.
The innovation that makes these clocks different is that they employ optical frequencies, far greater than the microwave frequencies employed by earlier cesium atomic clocks. The change makesit possible to achieve much higher resolution and lower uncertainty in keeping track of time.
The Multiplexing Breakthrough: Multiple Clocks in One Setup
A significant breakthrough came in the form of work by researchers at the University of Wisconsin–Madison, headed by Shimon Kolkowitz. They were able to pack six individual clocks into one vacuum chamber, each with its own set of strontium atoms. Rather than comparing a single clock to a laser, they compared the clocks to one another—an approach that bypassed problems that arose from laser instability.
This configuration introduced a vast improvement: the clocks remained synchronized for far longer, adding a factor of 270 to coherence time. The group now could measure time differences so minute that two clocks would only run out of sync by a single second after 300 billion years. To put it into perspective, that’s 20 times older than the universe itself.
Probing the Universe: Using Time to Test Physics
These extremely accurate clocks are not merely about being always on time. They are instruments of great power for probing the very fabric of the universe. Jun Ye’s group at JILA in Colorado employed one such clock to measure gravitational redshift—the dilation of time due to gravity—over an incredibly modest height difference of just a millimeter. Their findings provided a striking validation of Einstein’s general relativity at an unimaginably fine resolution.
Meanwhile, at Wisconsin–Madison, the multiplexed clocks of the team are being called on in the hunt for dark matter and gravitational waves. By comparing the way clocks tick a little bit differently at slightly different spots or slightly different conditions, they can pick up minute differences that may be a sign of completely new physics.
Bringing the Lab to the Field: A Leap in Portability
Until now, the best clocks required enormous, ultra-stable lasers and could not travel beyond a lab. But the times are changing rapidly. The Wisconsin–Madison physicists demonstrated that even with a portable, commercially available laser, their multiplexed clock produced world-class performance. That is to say that those high-precision clocks might be employed in the field very soon and completely change applications such as navigation, data networks, and even the measurement of Earth’s gravity field.
In the U.K., another group constructed a mini optical lattice clock that weighed less than 75 kilograms and fit inside a trunk. They moved it over 200 kilometers and had it operational within less than 90 minutes—testimony that first-rate timekeeping needn’t remain within a laboratory.
The Next Era of Timekeeping
As such, optical lattice clocks shrink, harden, and cheapen; their potential simply widens. They could redefine the “second” in the international measuring system, greatly improve GPS accuracy, and track subtle changes in Earth’s gravity with never-before-seen sensitivity. A network of such clocks could even help researchers search for dark matter or test the boundaries of Einstein’s theories.
The competition to construct the ultimate clock is far from over—yet with optical lattice clocks at the forefront, the future of timekeeping has never been more thrilling.
