Squeezing an Optical Atomic Clock Into a Briefcase

WALKING INTO Jun Ye's lab at the University of Colorado Boulder is a bit like walking into an electronic jungle. There are wires strung across the ceiling that hang down to the floor. Right in the middle of the room are four hefty steel tables with metal panels above them extending all the way to the ceiling. Slide one of the panels to the side and you'll see a dense mesh of vacuum chambers, mirrors, magnetic coils, and laser light bouncing around in precisely orchestrated patterns. ¶ This is one of the world's most precise and accurate clocks, and it's so accurate that you'd have to wait 40 billion years-or three times the age of the universe-for it to be off by one second. ¶ What's interesting about Ye's atomic clock, part of a joint endeavor between the University of Colorado Boulder and the National Institute of Standards and Technology (NIST), is that it is optical, not microwave like most atomic clocks. The ticking heart of the clock is the strontium atom, and it beats at a frequency of 429 terahertz, or 429 trillion ticks per second. It's the same frequency as light in the lower part of the red region of the visible spectrum, and that relatively high frequency is a pillar of the clock's incredible precision. Commonly available atomic clocks beat at frequencies in the gigahertz range, or about 10 billion ticks per second. Going from the microwave to the optical makes it possible for Ye's clock to be tens of thousands of times as precise. © 1964-2012 IEEE.