Researchers have pinpointed an ideal spot in a crystal lattice to embed thorium 229 atoms, a discovery that might pave the way for an ultra-accurate nuclear clock. Detailed in a Science study, this could push timekeeping precision far beyond current atomic clocks.
Today's atomic clocks are incredibly precise, losing less than a second over the universe's age. But they rely on complex systems and shielding, making them bulky. The new method targets the atom's nucleus, focusing on neutron energy transitions, potentially boosting accuracy tenfold.
Andreas Schumm from the Vienna University of Technology led the research, exploring the crystal structure needed. They found thorium 229, which can be manipulated with ultraviolet lasers, offers a unique chance due to its low nuclear transition energy, allowing a more effective clock mechanism.
After 15 years of trials, Schumm's team developed a way to grow solid calcium fluoride crystals with thorium 229 impurities. These crystals, tiny and transparent, are designed to house thorium atoms with minimal interference. Schumm compared crystal growing to alchemy, highlighting its trial-and-error nature.
Using a custom ultraviolet laser, researchers illuminated the crystal for 60 seconds, then monitored the decay of excited nuclei over five minutes. They discovered thorium atoms can occupy four different sites in the lattice. One site emitted light at a single wavelength, indicating a uniform electric field perfect for clock functionality.
“The data in this paper is something we’ve all wanted to see for some time, ” said Eric Hudson, a physicist at the University of California, Los Angeles. “This is a very important result for the research on the solid-state nuclear clock, ” added Ekkehard Peik, head of the Time and Frequency Department at the National Metrology Institute in Germany.
Building on their work, Schumm and his team have already created initial clock prototypes and patented a miniaturization method. They aim to shift from lab-sized models to compact versions, potentially fitting in a shoebox, useful for precise timekeeping in data centers during outages.
Meanwhile, a team led by Shiqian Ding at Tsinghua University in China has also progressed in this field, developing a prototype nuclear clock with similar results using a stronger laser on a crystal with less thorium 229. Schumm noted the rapid advancements in this area.
While Schumm didn’t specify when they might surpass current atomic clocks, he is confident their prototypes will improve by at least three orders of magnitude by year-end. The focus is on refining the design and reducing clock size, potentially transforming timekeeping technology.
