![]() “When atoms in the gaseous phase are very hot, they’re moving apart and colliding with each other,” he says. Ye says the ultracold temperatures turn the atoms into what is known as a quantum gas. One person lives in each house and neighbours are never allowed in,” says Ye. “Imagine a scenario where you have single-person housing in a city block. They cooled the atoms to -273˚C and trapped each one in its own spot to control the interactions between them. ![]() The latticework enabled the researchers to survey atoms that were much more densely packed together – 10 trillion atoms per cubic centimetre compared with previous clocks with 10 billion atoms per cubic centimetre – and have better control of those atoms’ interactions, minimising how often they crash into each other. But if you pack in too many, the signal can get blurred by collisions between atoms. To build a more precise clock, Ye and his team designed a 3D structure that let them measure signals from more atoms at once within the width of the laser beam. Now, Ye’s group has built a strontium clock that is so precise, out of every 10 quintillion ticks only 3.5 would be out of sync – the first atomic clock ever to reach that level of precision. Previous caesium clocks kept time accurately to within a second over the course of 300 million years. “In 2014, the world’s most accurate optical clock wouldn’t lose or gain one second in the entire age of the universe,” says Jun Ye at the University of Colorado at Boulder. ![]()
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