Two atomic clocks have been connected using quantum entanglement 鈥� a property that intrinsically links them so that changes in one instantaneously affect the other. The connection makes it easier to synchronise the clocks, which could be used to make more accurate measurements of dark matter and gravity.
Atomic clocks consist of atoms that are very precisely controlled by lasers. Each 鈥渢ick鈥� corresponds to a frequent and measurable change in energy that occurs in the atoms鈥� electrons. The result is a clock that is hundreds of millions of times more accurate than a household clock.
However, precisely syncing up two atomic clocks is challenging because measuring them disturbs them enough to introduce errors. Entangling them would mean having to take fewer measurements.
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at the University of Oxford and her colleagues entangled聽two atomic clocks that were 2 metres apart and each made using a single strontium atom.
To entangle the clocks, the team first used a laser to give the strontium atoms energy so that they emitted a blue light. The blue light from each atom then travelled through an optical fibre into a device called a Bell state analyser, which manipulated their quantum states so that the original atoms became entangled.
Measuring one clock would now provide information about both. This meant the researchers were able to measure the difference in how often the two clocks ticked with an uncertainty of around 7 per cent, compared with 28 per cent if they weren鈥檛 entangled.
The researchers could decrease the uncertainty values by spending more time taking measurements, but, crucially, getting the same accuracy took half the time with entangled clocks compared with unentangled ones.
The laws of quantum physics say that measuring ticking frequency with perfect accuracy is impossible, says co-author at the University of Oxford. But we got very close to the limit in this experiment, he says.
at the University of Wisconsin-Madison says that if the new experiment can be repeated with more clocks or with the clocks further apart, perhaps in two separate labs, it could advance studies of dark matter or gravity. For instance, if a clump of dark matter moved between the entangled clocks, the difference between their ticking frequencies would change in response, and these networks could detect the change very precisely. Small changes in the strength of gravity would have the same effect, he says.
Reference: Nature,
