NIST’s Aluminum Ion Clock Achieves Unprecedented Accuracy

USA: NIST’s Aluminum Ion Clock Achieves Unprecedented Accuracy

A new record for timekeeping precision was announced on July 14, 2025, when researchers at the National Institute of Standards and Technology (NIST) reported that their aluminum‑ion optical clock can measure time with an accuracy of 19 decimal places. The achievement represents a 41% improvement over the previous best and makes the device 2.6 times more stable than any other ion‑based clock.

Technical Advances in Accuracy

The clock’s enhanced performance stems from a series of hardware upgrades, including a redesigned ion trap, a titanium vacuum chamber, and a more stable interrogation laser. Together these changes reduced systematic uncertainty to 5.5×10⁻¹⁹, enabling the clock to reach the new accuracy benchmark.

Quantum Logic Spectroscopy Approach

To overcome the difficulty of directly cooling aluminum ions, the team employed a “buddy system” that pairs each aluminum ion with a magnesium ion. The magnesium ion is readily laser‑cooled and transfers its motion to the aluminum ion, allowing the clock’s state to be read out via quantum logic spectroscopy.

Improved Ion Trap Design

Excess micromotion caused by electrical imbalances in the trap was identified as a source of error. Engineers addressed the issue by mounting the trap on a thicker diamond wafer and applying thicker gold coatings to the electrodes, which reduced resistance and stabilized the ions’ motion.

Vacuum System Redesign

Hydrogen outgassing from a conventional steel chamber introduced background gas collisions that limited continuous operation. Replacing the chamber with a titanium vessel lowered hydrogen presence by a factor of 150, extending uninterrupted run times from minutes to several days.

Laser Stability Enhancements

The clock’s interrogation laser was linked via a 3.6‑kilometer fiber link to an ultrastable strontium lattice laser at JILA. This connection allowed the aluminum‑ion system to probe the ions for a full second—up from 150 milliseconds—cutting the averaging period needed to reach the 19th decimal place from three weeks to roughly a day and a half.

Implications for Metrology and Science

Beyond redefining the SI second, the improved clock is expected to support geodetic measurements, tests of fundamental physics, and the development of quantum technologies. Researchers anticipate that scaling the number of ions or creating entangled states could further enhance measurement capabilities.

This report is based on information from NIST, licensed under Public Domain (U.S. Government Work). Source: Official U.S. Government release.