Researchers Unveil World’s Most Accurate Clock After 20 Years

Researchers at the National Institute of Standards and Technology (NIST) have achieved a remarkable milestone by developing the world’s most accurate clock. This new optical atomic clock, which took two decades to build, utilizes a single trapped aluminum ion and boasts an astonishing fractional frequency uncertainty of 5.5 × 10−19. This level of precision means that the clock would take longer than the current age of the universe to lose or gain just one second.

The clock’s fractional frequency stability is equally impressive, rated at 3.5 × 10−16 / √τ seconds. This makes it 2.6 times more stable than any previous ion clock. Researchers evaluate optical clocks based on two primary criteria: accuracy, which refers to how closely they align with “true” time, and stability, which denotes how consistently they can measure it.

Two Decades of Innovation

The record-breaking achievement is the culmination of 20 years of continuous enhancements to various components of the aluminum ion clock, including its laser, ion trap, and vacuum chamber. “It’s exciting to work on the most accurate clock ever,” said Mason Marshall, a NIST researcher and the first author of the study.

The clock operates using quantum logic spectroscopy of a single 27Al+ ion, with a 25Mg+ ion trapped alongside it. The magnesium ion assists with sympathetic cooling and helps researchers indirectly read the state of the aluminum ion. Aluminum is particularly suited for timekeeping due to its stable “ticks,” which are less influenced by temperature fluctuations and magnetic fields. However, controlling aluminum with lasers proves challenging, making magnesium a valuable partner in this process.

Significant Upgrades and Future Potential

Key improvements to the clock include extending the Rabi probe duration to one second. This advancement was made possible by transferring laser stability from a remote cryogenic silicon cavity located in Jun Ye‘s lab at JILA through a 3.6 km fiber link. This innovation reduced instability by a factor of three compared to earlier aluminum ion clocks.

The research team also redesigned the ion trap to minimize excess micromotion, which can disrupt timing accuracy. By using a thicker diamond wafer and adjusting the gold coatings on the electrodes, they addressed electrical imbalances that contributed to this issue. Additionally, the vacuum chamber was reconstructed from titanium, leading to a significant reduction in background hydrogen gas by 150 times and decreasing collisional shifts. As a result, the clock can now operate for days without needing to reload ions.

Researchers have also developed a method to measure the ac magnetic field from the radio-frequency trap in a direction-sensitive manner, eliminating uncertainty related to field orientation. These enhancements allow the clock to achieve 19-decimal-place precision in approximately 36 hours, a significant improvement from the previous three-week requirement.

“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,” remarked Willa Arthur-Dworschack, a graduate student involved in the research.

The implications of this achievement are profound, with the potential to redefine the second with unprecedented precision. It could also pave the way for new advancements in Earth science and fundamental physics, including investigations into whether the constants of nature remain consistent over time.