YOU might think a clock with an accuracy of 1 second in 60 million years would be tough to beat. Yet atomic clocks using lattices of strontium atoms are poised to do just that, so becoming the gold standard for timekeeping.
The clocks could allow more accurate GPS devices and new measurements of the fundamental constants that govern our universe.
The best clocks at present are based on caesium and 鈥渢ick鈥� every time electrons in a single ion oscillate between energy states. That happens 9,192,631,770 times each second, but physicists want to find an even faster pulse to create more accurate clocks. The electrons of strontium atoms switch energy levels more than a thousand times as often, but until now strontium clocks have played second fiddle to their caesium rivals because of the difficulty in measuring the higher-frequency ticks.
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Now Jun Ye of the University of Colorado at Boulder and researchers at the US National Institute of Standards and Technology have created a strontium clock with the accuracy of the best caesium-ion clocks (Science, vol 314, p 1430).
To build their clock, the team used laser beams to create a lattice of light waves that trapped strontium atoms. They then shone a separate probe laser at the lattice and tuned that laser鈥檚 frequency until it began to resonate, indicating that its frequency matched that of the oscillating strontium electrons. The resonant frequency of the probe laser can then be used to measure time.
In 2005 researchers in Japan created a strontium clock using the same principle (快猫短视频, 21 May 2005, p 29), but it had an error margin of 27 oscillations per second in measuring the frequency. Ye has achieved an error margin of just 1.8 oscillations per second. 鈥淐aesium will eventually go out of fashion,鈥� he says, as ever steadier atom-trapping lasers should allow strontium to overtake it.
