Superprecise timekeepers based on atomic nuclei could be tested as soon as this year
Researchers are attempting to build the world’s first nuclear clock. This is a view inside the vacuum chamber that holds crystals doped with the isotope thorium-229, which can be excited by a laser. This device would keep time by measuring energy transitions in the nuclei of atoms and could become the most precise clock on the planet.
Researchers are attempting to build the world’s first nuclear clock. This is a view inside the vacuum chamber that holds crystals doped with the isotope thorium-229, which can be excited by a laser.. This device would keep time by measuring energy transitions in the nuclei of atoms and could become the most precise clock on the planet. Decades ago, scientists predicted that the isotope thorium-229 could be used in such a clock, but they couldn’t pin down its unusual nuclear energy transition. That feat,Now, such a clock is “way closer than people think,” says Eric Hudson, a physicist at the University of California, Los Angeles, who is working on one. “You’ll see nuclear-clock measurements in 2026, I’m sure.”. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. Nearly a dozen research teams, spread across China, Europe, Japan and the United States, are closing in on assembling the components of such a clock, including a source ofTh — which is radioactive — and a powerful continuous-wave ultraviolet laser to excite the energy transition. At the American Physical Society Global Physics Summit in Denver, Colorado, this week, researchers provided updates on their progress, including details of laser development. Claire Cramer, the executive director of quantum science at the University of California, Berkeley, who was in attendance, expressed optimism about the potential of solid-state nuclear clocks: “This is a really, really promising technology for commercial applications.” That’s because nuclear clocks could be resilient to noise and have a compact design for use outside the laboratory. They might also surpass the precision of optical atomic clocks, the field’s current top timekeepers, which lose only one second every 40 billion years.Timekeeping, whether in a pocket watch or a physics lab, boils down to counting rapid, regular events — the ‘ticks’ in any clock. In optical atomic clocks, these events are the hopping of electrons in an atom between a ground and an excited energy state. A laser with a wavelength in the 350- to 750-nanometre range excites this transition, which can ‘tick’ trillions of times per second.Th. These have the same number of protons and neutrons, but different energies depending on how the particles are squeezed together in the nucleus.Th transition remained uncertain. Several independent research groups began to close in on an answer a few years ago. The search culminated in a 2024 experiment led by Chuankun Zhang, a physicist now at the California Institute of Technology in Pasadena, and Jun Ye, a physicist at the JILA research institute in Boulder, Colorado. Using a frequency comb — a laser with about 30 million frequencies that can hit a crystal simultaneously — Zhang, Ye and their colleagues pinpointed the transition with ultra-high precision. To access it in a functioning nuclear clock, however, scientists now need a powerful and stable continuous-wave laser with an ultraviolet wavelength of around 148 nanometres. And no such laser has been made. A group based at Tsinghua University in Beijing, China, has taken some of the most promising strides towards constructing one. Last month, the team reported inthat it had delivered 100 nanowatts of power at 148.4 nm. Although researchers have praised the advance, some at the APS meeting expressed hesitation about the laser’s long-term prospects, because it requires heating toxic cadmium vapour to 550 ºC. Another approach converts an optical laser’s wavelength to 148 nm with a specialized crystal. Ye said that preliminary tests with a particular crystal have provided a nearly stable 40 microwatts of power. He did not disclose the material’s identity, instead saying that it is “tremendously promising”. But his group collaborates with IPG Photonics, a laser manufacturer based in Marlborough, Massachusetts, whichThe community hasn’t nailed a solution yet, Hudson said. “But my opinion is, this is a technical problem that no one needed to solve before, and now we will solve it.”229 Th ions used, but it is limited by stability. A stable nuclear clock requires a narrow linewidth for the nuclear transition — that is, its signal must have a narrow range of frequencies. Using a calcium fluoride crystal infused withTh ions, Ye’s group has so far achieved a signal with a linewidth of around 30 kilohertz — too big for a stable clock. It’s not yet clear what’s causing the large linewidth, but researchers at the meeting suspect impurities in the calcium fluoride. Some are exploring other types of crystal, and even thin crystalline films, which are easier to make and have fewer impurities. Hudson is particularly optimistic about thorium tetrafluoride — a radioactive coating that used to be popular for camera lenses — and thorium oxide.Th might not offer enough accuracy for a nuclear clock, because they naturally broaden the clock signal’s linewidth. This is why researchers are pursuing ion traps, in which ions ofTh are cooled and suspended at ultra-low temperatures, down to microkelvin. “If you want to be really accurate, then you will do a trapped ion” experiment, Ye says. So far, no one has managed that withIt’s Time to Stand Up for Sciencehas served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too., you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.There has never been a more important time for us to stand up and show why science matters. I hope you’ll support us in that mission.
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