At 11:30 one night in May 2024, a graduate student, Chuankun Zhang, saw a signal that physicists have sought for 50 years. As a peak rose from the static on his monitor at the research institute JILA in Boulder, Colorado, Zhang dropped a screenshot in a group chat with his three lab mates. One by one they hopped out of bed and trickled in. After several sanity checks to make sure that what they were looking at was real — a signal from a thorium-229 nucleus switching between two states, known as the “nuclear clock” transition — the young researchers took a selfie to commemorate the moment. Time stamp: 3:42 a.m.
At their weekly meeting later that morning with their group leader, Jun Ye (opens a new tab), builder of the world’s most precise atomic clock, they decided to play it cool. “They were all poker-faced,” Ye said, until Zhang shared a slide displaying the long-sought peak. Tears flooded Ye’s eyes as the group clinked glasses of champagne at 9:30 a.m.
The group’s measurement, reported (opens a new tab) on September 4, 2024, in the journal Nature, is the third observation of the thorium-229 transition published within the last four months, coming on the heels of results from Germany and California. But the new measurement is millions of times more precise than the others, and it marks the end of a marathon search for the exact laser frequency needed to induce the nuclear clock transition. “This paper is an incredible technical achievement,” said Hannah Williams (opens a new tab), a physicist at Durham University in the United Kingdom who was not involved in the work.
This is a big deal. The potential ramifications are enormous.
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