A team of researchers at the National Institute of Standards and Technology (NIST) has developed the world’s most accurate clock, a feat that took two decades of meticulous engineering and research. This groundbreaking optical atomic clock, built around a single trapped aluminum ion, achieves a fractional frequency uncertainty of 5.5 × 10−19. This level of precision means it would take longer than the age of the universe for it to lose or gain a second.
The clock’s performance is further enhanced by its fractional frequency stability of 3.5 × 10−16 / √τ seconds, making it 2.6 times more stable than any other ion clock currently available. Researchers assess optical clocks based on two critical metrics: accuracy, which measures how closely they align with “true” time, and stability, which evaluates consistency in timekeeping.
Innovations in Design and Technology
The achievement is the result of continuous improvements over 20 years involving the aluminum ion clock’s 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 study’s lead author.
The clock operates by using quantum logic spectroscopy on a single 27Al+ ion, with a 25Mg+ ion trapped alongside it to assist with sympathetic cooling and to facilitate measurement of the aluminum ion’s state. Aluminum is particularly effective for timekeeping due to its steady “ticks” that are less influenced by temperature or magnetic fields. However, controlling aluminum ions with lasers presents challenges. The magnesium ion serves as a partner, allowing for easier handling while enabling researchers to indirectly measure the aluminum ion.
Significant upgrades were made, including extending the Rabi probe duration to one second, achieved through a 3.6 km fiber link that transferred laser stability from a remote cryogenic silicon cavity located in Jun Ye’s lab at JILA. This advancement reduced instability by a factor of three compared to previous aluminum ion clocks.
Engineering Breakthroughs Enhance Performance
The design of the ion trap was also re-engineered to minimize excess micromotion—tiny movements that can disrupt precise timing. Researchers utilized a thicker diamond wafer and adjusted gold coatings on the electrodes to address electrical imbalances. Additionally, the vacuum chamber was reconstructed from titanium, which significantly decreased background hydrogen gas by a factor of 150. This reduction lowered collisional shifts, allowing the clock to operate for days without the need to reload ions.
Further refinements included measuring the alternating current magnetic field from the radio-frequency trap in a direction-sensitive manner, effectively removing the uncertainty caused by the orientation of the field. These enhancements enable the clock to achieve 19-decimal-place precision in approximately 36 hours, a considerable improvement compared to the previous timeline of three weeks.
“This platform positions us to explore new clock architectures—like increasing the number of clock ions and even entangling them—enhancing our measurement capabilities,” stated graduate student Willa Arthur-Dworschack.
The implications of this achievement extend beyond timekeeping. It has the potential to redefine the second with unprecedented precision and could facilitate advancements in Earth science and fundamental physics, including investigations into whether the constants of nature remain constant.
As this research advances, it highlights the remarkable progress made in the field of precision measurement and its far-reaching impacts on science and technology.
