The National Institute of Standards and Technology (NIST) has developed the world’s most accurate clock, a groundbreaking optical atomic clock built around a single trapped aluminum ion. This innovative clock is so precise that its fractional frequency uncertainty measures at 5.5 × 10−19, meaning it would take longer than the age of the universe for it to lose or gain a single second. This achievement marks a significant milestone after 20 years of continuous improvements.
Precision and Stability Redefined
The new optical atomic clock boasts a fractional frequency stability of 3.5 × 10−16 / √τ seconds, making it 2.6 times more stable than any previously existing ion clock. The performance of optical clocks is evaluated based on two key factors: accuracy, which indicates how close they come to measuring “true” time, and stability, which reflects how consistently they can maintain that measurement.
Mason Marshall, a researcher at NIST and the study’s lead author, expressed his enthusiasm: “It’s exciting to work on the most accurate clock ever.” The clock utilizes quantum logic spectroscopy on a single 27Al+ ion, with a 25Mg+ ion trapped alongside to aid in sympathetic cooling and to facilitate measurement of the aluminum ion’s state.
Innovative Upgrades Enhance Performance
Aluminum is particularly effective for timekeeping, as its “ticks” are highly consistent and less susceptible to variations caused by temperature or magnetic fields. However, controlling aluminum ions with lasers is challenging. The magnesium ion serves as a partner by cooling the aluminum ion, thus enabling researchers to measure it indirectly.
A significant enhancement in the clock’s performance was achieved by extending the Rabi probe duration to 1 second. This improvement was made possible by transferring laser stability from a remote cryogenic silicon cavity in Jun Ye’s lab at JILA through a 3.6 km fiber link. This advancement reduced instability by a factor of three compared to earlier models of aluminum ion clocks.
Further refinements included redesigning the ion trap to minimize excess micromotion, which can disrupt timing accuracy. Researchers employed a thicker diamond wafer and adjusted the gold coatings on the electrodes to address electrical imbalances. The vacuum chamber was also reconstructed using titanium, leading to a reduction in background hydrogen gas by 150 times. This change significantly lowered collisional shifts, allowing the clock to operate for days without needing to reload ions.
In addition, the research team measured the alternating current (AC) magnetic field from the radio-frequency trap in a direction-sensitive manner, effectively eliminating uncertainties associated with field orientation. These enhancements enable the clock to achieve 19-decimal-place precision in approximately 36 hours, a remarkable improvement from the previous requirement of three weeks.
Graduate student Willa Arthur-Dworschack remarked, “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.”
The implications of this achievement extend beyond mere timekeeping. The new clock technology could help redefine the second with unprecedented precision and open new avenues in Earth science and fundamental physics, including investigating whether the constants of nature are truly constant.
This advancement from NIST not only represents a significant technical achievement but also possesses the potential to reshape our understanding of time itself.