Ekkehard Peik thought it would take only a few months to create the basic ingredients of a radical new clock. That was back in 2001, when he and his colleague Christian Tamm proposed a device with the potential to be even more precise and portable than the world’s best atomic clocks.
Peik’s estimate was off by more than two decades. But this year, his team and two other groups managed to finally achieve what he and Tamm had proposed, generating the first tick of a clock based on tiny energy shifts inside an atomic nucleus.
The world’s best atomic clocks rely on the energy transitions of electrons that orbit an atomic nucleus. These clocks are so accurate that they gain or lose only a second every 40 billion years.
Peik and Tamm, both physicists at the PTB, Germany’s national metrology institute in Braunschweig, came up with the idea of a nuclear approach. “We thought we could very quickly do a kind of demonstration experiment,” says Peik. For more than a year, they tried different ways to nudge nuclei of radioactive thorium-229 into an excited state. Then they would need to tune a laser to the energy of the nuclei’s transition and eventually use its frequency to mark time. “But the experiments all failed,” he says. The pair published their unproven proposal in 2003 (E. Peik and C. Tamm Europhys. Lett. 61, 181; 2003).
Tamm later retired but Peik kept at the problem. His perseverance paid off this year when his was the first of three groups to excite the nucleus to make it ‘tick’. There is still a way to go before this kind of system can replace the most precise clocks. But a starting gun has been fired. “Now everybody wants a piece,” says Thorsten Schumm, an atomic physicist and Peik’s collaborator at the Vienna University of Technology.
Peik always found precision clocks fascinating. He was thrilled by their fusion of fundamental physics and practical applications. The idea of creating an entirely new kind of clock came when his PTB colleague, metrologist Uwe Sterr, noted a quirk in the nuclear physics literature. Studies showed that the thorium-229 nucleus must have a strangely low-energy excited state — one so low that it would be possible to induce that transition with a precision laser. For nuclear physicists, this transition was a curiosity. But Peik and Tamm saw that they could use it to make a clock. “It was quite logical for us to follow up,” says Peik. “Nobody had done this.”
