Spooky Atomic Clocks

"The best atomic clocks on Earth today are stable to about one part in 10¹⁵," notes Kuzmich. That means an observer would have to watch the clock for 10¹⁵ seconds or 30 million years to see it gain or lose a single second.

Click on the image to learn more. Lasers are a key ingredient of atomic clocks - both the ordinary and entangled variety.

The precision of an atomic clock depends on a few things, including the number of atoms being used. The more atoms, the better. In a normal atomic clock, the precision is proportional to the square-root of the number of atoms. So having, say, 4 times as many atoms would only double the precision. In an entangled atomic clock, however, the improvement is directly proportional to the number of atoms. Four times more atoms makes a 4-times better clock.

Using plenty of atoms, it might be possible to build a "maximally entangled clock stable to about one part in 10¹⁸," says Kuzmich. You would have to watch that clock for 10¹⁸ seconds or 30 billion years to catch it losing a single second.

Kuzmich plans to use the lasers already built-in to atomic clocks to create the entanglement.

"We will measure the phase of the laser light passing through the cloud of atoms," he explains. Measuring the phase "tweaks the laser beam," and if the frequency of the laser has been chosen properly, tweaking the beam causes the atoms to become entangled. Or, as one quantum physicist might say to another, "such a procedure amounts to a quantum non-demolition (QND) measurement on the atoms, and results in preparation of a Squeezed Spin State."

How soon an entangled clock could be built - much less launched into space aboard a hypothetical new generation of GPS satellites - is difficult to predict, cautions Kuzmich. The research is still at the stage of just demonstrating the principle. Building a working prototype is probably several years away.

But thanks to research such as this, having still-better atomic clocks available to benefit science and technology is only a matter of time.