Physicists Just Entangled A Pair of Atomic Clocks Six Feet Apart


Entangling atoms in clocks increases their precision. (Willem Douven/EyeEm/Getty Images)

Very few things in the Universe keep the beat as reliably as an atom's pulse. 

Yet even the most modern 'atomic' clocks based on variations of these quantum timekeepers lose count when pushed to their limits. 

Physicists have known for some time that tangling atoms can help tie particles down enough to squeeze a little more tick from every tock, yet most experiments have only been able to show this on the smallest of scales. 

A team of researchers from the University of Oxford in the UK have pushed that limit to a distance of two meters (about six feet), showing that the mathematics continues to hold true over larger spaces. 

Not only could this increase the overall precision of optical atomic clocks, it allows for a level of comparison in the split-second timing of multiple clocks to a degree that could divulge previously undetectable signals in a range of physical phenomena. 

As the name indicates, optical atomic clocks utilize light to probe the movements of atoms to keep time. 

Like a child on a swing, parts of atoms whizz back and forth under a consistent set of constraints. All that's needed is a reliable kick, such as a photon from a laser, to place the swinging in motion. 

These in turn can be ironed out by studying the atom multiple times, a solution not without its own problems. 

A 'single shot' studying with the right kind of laser pulse would be ideal. Physicists know that the uncertainty of this approach can be increased if the atom being measured has already had its fate entangled with another. 

Entanglement is at once an instinctive and bizarre concept. According to quantum mechanics, objects can't be said to have a value or state until they're noticed. 

If they're already piece of a bigger system – might be through an exchange of photons with other atoms – all parts of the system will be fated to deliver a relatively expected result. 

It's like flipping couple of coins from the same wallet, knowing if one comes up heads the other will come up tails even as it rotates in the air. 

Both 'coins' in this case were a pair of strontium ions, entangled with a photon that was sent down a small length of optic fiber. 

The experiment itself didn't produce any revolutionary levels of precision in optic atomic clocks, though it wasn't planned to. 

Instead, the team proved by entangling the charged atoms of strontium, they could reduce the uncertainty of the measurement under conditions that should allow them to increase precision in the future. 

Knowing macroscopic distances of a few meters gives no challenge, it's now theoretically possible to entangle optical atomic clocks around the world to increase their precision. 

Compressing a little more confidence out of every tick-tock of an atomic clock could be just what we are required to measure small differences in time produced by masses over the smallest of distances, a tool that might lead the way to quantum theories of gravity. 

Even outside of research, using entanglement to decrease uncertainty in quantum measurements could have programs in anything from quantum computing to encryption and communications. 

This research was originally published in Nature. 

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