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Share sensitive information only on official, secure websites. https://www.nist.gov/news-events/news/2025/07/ nist-ion-clock-sets-new-record-most-accurate-clock-world National Institute of Standards and Technology National Institute of Standards and Technology Search NIST [ ] Search Menu Close * Publications * What We Do + All Topics + Advanced communications + Artificial intelligence + Bioscience + Buildings and construction + Chemistry + Cybersecurity + Electronics + Energy + Environment + Fire + Forensic science + Health + Information technology + Infrastructure + Manufacturing + Materials + Mathematics and statistics + Metrology + Nanotechnology + Neutron research + Performance excellence + Physics + Public safety + Quantum information science + Resilience + Standards + Transportation * Labs & Major Programs + Assoc Director of Laboratory Programs + Laboratories o Communications Technology Laboratory o Engineering Laboratory o Information Technology Laboratory o Material Measurement Laboratory o Physical Measurement Laboratory + User Facilities o NIST Center for Neutron Research o CNST NanoFab + Research Test Beds + Research Projects + Tools & Instruments + Major Programs o Baldrige Performance Excellence Program o CHIPS for America Initiative o Manufacturing Extension Partnership (MEP) o Office of Advanced Manufacturing o Special Programs Office o Technology Partnerships Office * Services & Resources + Measurements and Standards o Calibration Services o Laboratory Accreditation (NVLAP) o Quality System o Standard Reference Materials (SRMs) o Standard Reference Instruments (SRIs) o Standards.gov o Time Services o Office of Weights and Measures + Software + Data o Chemistry WebBook o National Vulnerability Database o Physical Reference Data o Standard Reference Data (SRD) + Storefront + License & Patents + Computer Security Resource Center (CSRC) + NIST Research Library * News & Events + News + Events + Blogs + Feature Stories + Awards + Video Gallery + Image Gallery + Media Contacts * About NIST + About Us o Leadership o Organization Structure o Budget & Planning + Contact Us + Visit + Careers o Student programs + Work with NIST + History o NIST Digital Archives o NIST Museum o NIST and the Nobel + Educational Resources NEWS NIST Ion Clock Sets New Record for Most Accurate Clock in the World July 14, 2025 Share Facebook Linkedin X.com Email * NIST researchers have made the most accurate atomic clock to date -- one that can measure time down to the 19th decimal place. * This "quantum logic clock," under continuous development for 20 years, relies on quantum computing techniques that pair an electrically charged aluminum atom (ion) with a magnesium ion. * This new result contributes to the international effort to define the second with a much greater level of accuracy than before, enabling new scientific and technological advances. Four researchers pose standing around a large piece of scientific equipment covered with wiring and electronics. (From left to right) Mason Marshall, David Hume, Willa Arthur-Dworschack and Daniel Rodriguez Castillo stand in front of the aluminum ion clock at NIST. With its recent improvements, the clock can pave the way for the campaign to redefine the second as well as explore new ideas in physics. Credit: R. Jacobson/NIST There's a new record holder for the most accurate clock in the world. Researchers at the National Institute of Standards and Technology (NIST) have improved their atomic clock based on a trapped aluminum ion. Part of the latest wave of optical atomic clocks, it can perform timekeeping with 19 decimal places of accuracy. Optical clocks are typically evaluated on two levels -- accuracy (how close a clock comes to measuring the ideal "true" time, also known as systematic uncertainty) and stability (how efficiently a clock can measure time, related to statistical uncertainty). This new record in accuracy comes out of 20 years of continuous improvement of the aluminum ion clock. Beyond its world-best accuracy, 41% greater than the previous record, this new clock is also 2.6 times more stable than any other ion clock. Reaching these levels has meant carefully improving every aspect of the clock, from the laser to the trap and the vacuum chamber. The team published its results in Physical Review Letters. "It's exciting to work on the most accurate clock ever," said Mason Marshall, NIST researcher and first author on the paper. "At NIST we get to carry out these long-term plans in precision measurement that can push the field of physics and our understanding of the world around us." A hand holds a small square device in a clear case. Gold-colored electronics can be seen through the case. NIST physicist David Hume holds the newly modified ion trap for the aluminum ion clock. By modifying the trap, the aluminum ion and its magnesium ion partner were able to "tick" unperturbed. Credit: R. Jacobson/NIST The aluminum ion makes an exceptionally good clock, with an extremely steady, high-frequency "ticking" rate. Its ticks are more stable than those of cesium, which provides the current scientific definition of the second, said David Hume, the NIST physicist leading the aluminum ion clock project. And the aluminum ion isn't as sensitive to some environmental conditions, like temperature and magnetic fields. But the aluminum ion is kind of shy, Marshall explained. Aluminum is difficult to probe and cool with lasers, both necessary techniques for atomic clocks. The research group therefore paired the aluminum ion with magnesium. Magnesium doesn't have the beautiful ticking properties of aluminum, but it can be easily controlled with lasers. "This 'buddy system' for ions is called quantum logic spectroscopy," said Willa Arthur-Dworschack, a graduate student on the project. The magnesium ion cools the aluminum ion, slowing it down. It also moves in tandem with its aluminum partner, and the state of the clock can be read out via the magnesium ion's motion, making this a "quantum logic" clock. Even with this coordination, there was still an array of physical effects to characterize, said Daniel Rodriguez Castillo, also a graduate student on the project. "It's a big, complex challenge, because every part of the clock's design affects the clock," Rodriguez Castillo said. One challenge was the design of the trap where the ions are held, which was causing tiny movements of the ions, called excess micromotion, that were lowering the clock's accuracy. That excess micromotion throws off the ions' tick rate. Electrical imbalances at opposite sides of the trap were creating extra fields that disturbed the ions. The team redesigned the trap, putting it on a thicker diamond wafer and modifying the gold coatings on the electrodes to fix the imbalance of the electric field. They also made the gold coatings thicker to reduce resistance. Refining the trap this way slowed the ions' motion and let them "tick" unperturbed. Close-up photo of metal plate holding flat gold-colored device. Inset shows gray pixelation with green circle. The newly modified ion trap for NIST's aluminum ion clock, with an inset showing a CCD image of the aluminum-magnesium ion pair. The circle shows the position of the aluminum ion, which is dark to the camera as it can only be read out using quantum logic spectroscopy via the magnesium ion. Credit: NIST The vacuum system in which the trap must operate was also causing problems. Hydrogen diffuses out of the steel body of a typical vacuum chamber, Marshall said. Traces of hydrogen gas collided with the ions, interrupting the clock's operation. That limited how long the experiment could run before the ions needed to be reloaded. The team redesigned the vacuum chamber and had it rebuilt out of titanium, which lowered the background hydrogen gas by 150 times. That meant they could go days without reloading the trap, rather than reloading every 30 minutes. There was still one more ingredient they needed: a more stable laser to probe the ions and count their ticks. The 2019 version of the clock had to be run for weeks to average out quantum fluctuations -- temporary random changes in the ions' energy state -- caused by its laser. To reduce that time, the team turned to NIST's own Jun Ye, whose lab at JILA (a joint institute of NIST and the University of Colorado Boulder) hosts one of the most stable lasers in the world. Ye's strontium lattice clock, Strontium 1, held the previous record for accuracy. This was a team effort. Using fiber links under the street, Ye's group at JILA sent the ultrastable laser beam 3.6 kilometers (a little more than 2 miles) to the frequency comb in the lab of Tara Fortier at NIST. The frequency comb, which acts as a "ruler for light," allowed the aluminum ion clock group to compare its laser with Ye's ultrastable one. This process enabled the Ye lab's laser to transfer its stability to the aluminum clock laser. With this improvement, the researchers could probe the ions for a full second compared to their previous record of 150 milliseconds. This improves the clock's stability, reducing the time required to measure down to the 19th decimal place from three weeks to a day and a half. Three researchers in safety glasses are seen through a forest of hanging wires and other electronic and laser devices. (From left to right) Daniel Rodriguez Castillo, Willa Arthur-Dworschack and Mason Marshall work together on the aluminum ion clock at NIST in Boulder. This atomic clock sets a new record for accuracy. Credit: R. Jacobson/NIST With this new record, the aluminum ion clock contributes to the international effort to redefine the second to much greater levels of accuracy than before, facilitating new scientific and technological advances. The upgrades also drastically improve its use as a quantum logic testbed, exploring new concepts in quantum physics and building the tools needed for quantum technology, an exciting prospect for those involved. More importantly, by cutting down the averaging time from weeks to days, this clock can be a tool to make new measurements of Earth's geodesy and explore physics beyond the Standard Model, such as the possibility that the fundamental constants of nature are not fixed values but actually changing. "With this platform, we're poised to explore new clock architectures -- like scaling up the number of clock ions and even entangling them -- further improving our measurement capabilities," Arthur-Dworschack said. --------------------------------------------------------------------- Paper: Mason C. Marshall, Daniel A. Rodriguez Castillo, Willa J. Arthur-Dworschack, Alexander Aeppli, Kyungtae Kim, Dahyeon Lee, William Warfield, Joost Hinrichs, Nicholas V. Nardelli, Tara M. Fortier, Jun Ye, David R. Leibrandt and David B. Hume. High-stability single-ion clock with 5.5x10-19 systematic uncertainty. Physical Review Letters. Published online July 14, 2025. DOI: 10.1103/ hb3c-dk28 Metrology, Time and frequency metrology, Physics and Time and frequency Media Contact * Rebecca Jacobson [email protected] (303) 497-4789 Organizations * NIST Headquarters * + Laboratory Programs + o Physical Measurement Laboratory o # Time and Frequency Division # @ Ion Storage Group Related News New Atomic Fountain Clock Joins Elite Group That Keeps the World on Time Related Publications High-Stability Single-Ion Clock with 5.5 x 10^-19 Systematic Uncertainty Related Links Learn More About Atomic Clocks Sign up for updates from NIST Enter Email Address [ ] [Sign up] Released July 14, 2025, Updated July 15, 2025 Was this page helpful? National Institute of Standards and Technology logo HEADQUARTERS 100 Bureau Drive Gaithersburg, MD 20899 301-975-2000 Webmaster | Contact Us | Our Other Offices X.com Facebook LinkedIn Instagram YouTube Giphy RSS Feed Mailing List How are we doing? 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