# Physicists discover perfect crystal for nuclear clock Ideal crystal structure found for housing thorium 229 atoms in ultra-precise timekeeping - **Source:** [Scientific American Content: Global](https://brifing.si/source/4f066134-e06d-4415-87ef-305e3dc2aba6) - **Published:** 2026-08-20 - **Original article:** - **On Brifing:** https://brifing.si/s/455dc517-72a4-451f-a856-ef11e15c2c2e ## Limits of atomic clocks Today's best atomic clocks track electron transitions between energy levels, drifting less than one second over the universe's age. However, they require massive vacuum chambers and magnetic shielding. Scientists are now focusing on the atomic nucleus, developing a more stable system that monitors quantum state changes of individual neutrons for unprecedented precision. ## Thorium 229's unique property The thorium-229 isotope can be excited with ultraviolet lasers due to its unusually low nuclear transition energy, making it ideal for nuclear clocks. 2024 experiments proved this isotope could be controlled with simpler UV lasers instead of gamma-ray lasers required by other atoms. Th-229 remains the only known exception that enables this breakthrough approach to timekeeping. ## 15-year crystal quest Thorsten Schumm's team at Vienna University of Technology spent 15 years experimenting to find the perfect crystal structure for thorium atoms. They ultimately produced millimeter-sized transparent calcium fluoride crystals doped with small amounts of Th-229. Schumm notes, 'It looks like a tiny piece of glass, but mastering this took tens of thousands of hours of research.' ## Four distinct atomic positions Researchers mapped four different positions thorium atoms can occupy in the crystal lattice. Using a custom UV laser, they discovered three positions created uneven electric fields, while the fourth emitted light at a single wavelength indicating a perfectly uniform field. This fourth position provides ideal conditions for clock stability, marking a critical breakthrough. ## Prototypes and patents Following the discovery, the team built initial nuclear clock prototypes and patented a design small enough to fit on a chip. A separate team at China's Tsinghua University achieved comparable results. Schumm aims to develop clocks at least a thousand times more precise than current prototypes by year's end, signaling rapid progress in the field. ## Miniaturization focus The team currently prioritizes size reduction over absolute precision, planning to shrink the technology from lab-scale to shoebox-sized units. Schumm explains these could serve as backup time sources in data centers during satellite clock outages: 'They could maintain critical operations like financial transactions when conventional timing systems fail.' ## Scientific community's response Ekkehard Peik from Germany's National Metrology Institute called this 'a crucial result for solid-state nuclear clock research.' UCLA's Eric Hudson remarked, 'We've wanted to see this data for a long time.' Though not involved in the study, both experts recognize these findings as a significant milestone that could redefine precision timekeeping standards. ## Revolution in time measurement Nuclear clocks promise tenfold greater precision than atomic clocks, with crystal-embedded thorium atoms providing natural protection against external interference. This technology could transform fields from quantum computing to space navigation. Schumm's team observes accelerating progress, anticipating practical applications within years as the technology matures beyond laboratory prototypes. ## Sources covering this story - https://www.scientificamerican.com/article/physicists-pinpoint-the-perfect-crystal-site-for-an-ultra-accurate-nuclear-clock/ — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._