SINGAPORE TEAM BUILDS MOST ACCURATE ATOMIC CLOCK YET MADE

Researchers at the National University of Singapore's Centre for Quantum Technologies have built an atomic clock they say is the most accurate in the world, using a single charged atom of lutetium. The findings, published in the journal Nature, describe two lutetium-ion clocks with evaluated fractional uncertainties of 1.2 and 1.3 × 10⁻¹⁹. One report said this corresponds to losing a second in accuracy over roughly 264 billion years, while another put the figure at more than 260 billion years. Team leader Murray Barrett said: "I am confident that what we have now is the most accurate clock in the world." He added that he does not see how the clock could be surpassed in future.

Atomic clocks measure time using the frequency at which electrons in an atom shift energy levels when excited, with elements such as caesium traditionally used as the reference. More recently, scientists have tested faster-oscillating elements including strontium, aluminium and calcium. According to the researchers, lutetium's atomic structure makes it particularly well protected against disturbances from heat, magnetism and motion, allowing high accuracy across a wide range of conditions. The Singapore team's results are reported to surpass a calcium-ion clock from the Chinese Academy of Sciences in Wuhan, which recorded an uncertainty of 4.4 × 10⁻¹⁹, and an aluminium-ion clock unveiled by the US National Institute of Standards and Technology, which recorded 5.5 × 10⁻¹⁹.

The team built two independent lutetium clocks and compared them over 200 hours using a technique called correlation spectroscopy, which cancels out noise from their shared laser. The clocks agreed with each other to within 5.7 × 10⁻¹⁹, which the researchers describe as the most precise clock comparison carried out to date. The research has reportedly been published days before the General Conference on Weights and Measures meets in Versailles, where a draft resolution is said to show no consensus yet on replacing caesium as the basis for measuring the second. The researchers have been investigating lutetium's potential for roughly a decade.