Collaboration helps make JILA strontium atomic clock 'best in class'

The strontium and calcium clocks rely on the use of optical light, which has higher frequencies than the microwaves used in NIST-F1. Because the frequencies are higher, the clocks divide time into smaller units, offering record precision. Laboratories around the world are developing optical clocks based on a variety of different designs and atoms; it is not yet clear which design will emerge as the best and be chosen as the next international standard. The work reported in Science Express is the first optical atomic clock comparison over kilometer-scale urban distances, an important step for worldwide development of future standards.

"This is our first comparison to another optical atomic clock," says NIST/JILA Fellow Jun Ye, who leads the strontium project. "As of now, Boulder is in a very unique position. We have all the ingredients, including multiple optical clocks and the fiber-optic link, working so well. Without a single one of these components, these measurements would not be possible. It's all coming together at this moment in time."

NIST and JILA are home to optical clocks based on a variety of atoms, including strontium, calcium, mercury, aluminum, and ytterbium, each offering different advantages. Ye now plans to compare strontium to the world's most accurate clock, NIST's experimental design based on a single mercury ion (charged atom). The mercury ion clock was accurate to about 1 second in 400 million years in 2006 and performs even better today, according to Jim Bergquist, the NIST physicist who built the clock. The "best" status in atomic clocks is a moving target.

The development and testing of a new generation of optical atomic clocks is important because highly precise clocks are used to synchronize telecom networks and deep-space communications, as well as for navigation and positioning. The race to build even better clocks is expected to lead to new types of gravity sensors, as well as new tests of fundamental physical laws to increase understanding of the universe. Because Ye's group is able to measure and control interactions among so many atoms with such exquisite precision, the JILA work also is expected to lead to new scientific tools for quantum simulations that will help scientists better understand how matter and light behave under the strange rules governing the nanoworld.