Inside the Beating Heart of an Optical Atomic ClockS

Behold, the beating heart of a time machine! Or "clock", as most people call them, but this one is nothing like your grandfather's. This super-accurate timekeeper is an optical atomic clock built by the UK's National Physical Laboratory (NPL) and its tick is governed by a single ion of the element strontium.

The ion is trapped in an electromagnetic field within the small cube at the centre and cooled with lasers to just a fraction above absolute zero. The lasers are fired through three of the glass shafts emanating from the cube, but must be carefully directed out of the other side to prevent them scattering within the clock, which is why there are six shafts in total.

Once the ion is cooled, another laser makes it resonate between two energy states with an incredible regularity governed by quantum mechanics. It gives off a regular pulse of optical radiation exactly 444,779,044,095,485 times per second.

Don't be fooled by the orange light, it has nothing to do with the ion. It's just the hot glow of a wire that measures the quality of the vacuum within the cube. "You can see a bright spot in the middle, I hesitate to say whether that is fluorescence from an ion, but that's where it is located," says NPL's Patrick Gill.

Despite its sophistication, the clock's round face and equally spaced arms give it a familiar look. Gill, though, sees something totally different. "What with the arms coming off," he says, "I always call it the Buddha."

Image by Andrew Brookes/National Physical Laboratory


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