by Jacob Aron
It’s time for clocks to get a quantum boost. A network of ultra-precise atomic clocks could be linked together by the spooky property of quantum entanglement to create the ultimate world clock. Such a feat would allow all countries to agree on a precise measurement of time, while also creating a massive quantum sensor for probing cosmic mysteries.
Atomic clocks measure the microwave or optical frequency needed to make an atom’s electron jump from one energy level to another. The standard clock uses caesium atoms, which emit microwaves precisely 9,192,631,770 times per second. The signal is so incredibly regular that the latest caesium clock recently brought online in the US will not lose or gain a second in about 300 million years.
Timekeeping institutes around the world each have their own caesium clocks. They submit their time signal measurements to the International Bureau of Weights and Measures in Paris, France, which averages them and publishes a monthly newsletter that sets Coordinated Universal Time (UTC). But that means there is no real-time measure of a universally agreed standard time.
“UTC is a month in arrears, and there is a big drive to a real-time formulation,” says Leon Lobo of the National Physical Laboratory in Teddington, UK.
Eric Kessler at Harvard University and his colleagues think that quantum entanglement could provide a solution. When quantum objects such as atoms are entangled, measuring one has a direct and predictable effect on the other. If you were to entangle atomic clocks around the world and on orbiting satellites, it would help them to tick in unison, says Kessler.
“If you consider the individual clocks as pendulums, then entangling the different clock causes the different pendulums to swing perfectly in unison.”
His team evaluated existing clocks around the world and proposed a blueprint for a hypothetical network. The team calculates that a global quantum clock network would be about 100 times more precise than any individual clock. It would also be naturally protected from hackers, as the laws of quantum mechanics would immediately alert you to any attempts at eavesdropping. But entanglement is a very delicate state, so it may be a while before such a large quantum network could come online.
“There is no doubt that it is an ambitious proposal, and a long way to go,” says Kessler. “Substantial technological advances are needed, although all the different building blocks have in principle been demonstrated in a small scale.”
The quantum network is a worthy goal, says Ruxandra Bondarescu at the University of Zurich, Switzerland, because it could double as a sensor for conducting fundamental physics experiments. A highly sensitive global clock could be used to measure minute variations in Earth’s gravitational field, or to hunt for ripples in space-time known as gravitational waves, which would fractionally shift the clock’s tick.
“It has been hard to get funding for relatively impractical applications,” she says. “Such a network of clocks would be amazing if it could exist.”