The world’s most accurate clock has been developed by researchers at the National Institute of Standards and Technology (NIST). This optical atomic clock, which utilizes a single trapped aluminum ion, boasts an astonishing fractional frequency uncertainty of 5.5 × 10−19. To put this into perspective, it would take longer than the age of the universe for it to lose or gain a single second.
Notably, this clock exhibits a fractional frequency stability of 3.5 × 10−16 / √τ seconds, making it 2.6 times more stable than any other ion clock currently in existence. The advancements in this technology are a culmination of 20 years of dedicated research, focusing on enhancements to the aluminum ion clock’s laser, ion trap, and vacuum chamber.
Technological Innovations Propel Accuracy
The clock operates through a method known as quantum logic spectroscopy of a single 27Al+ ion. A secondary ion, 25Mg+, is trapped alongside the aluminum ion to facilitate sympathetic cooling and assist in measuring the state of the aluminum ion. Aluminum’s unique properties make it ideal for precision timekeeping, as its “ticks” are incredibly steady and less susceptible to temperature fluctuations or magnetic fields. However, controlling aluminum ions with lasers has proven challenging. This is where magnesium plays a crucial role, helping to cool the aluminum ion and allowing researchers to measure it indirectly.
One of the significant upgrades incorporated into this clock is the extension of the Rabi probe duration to 1 second. This improvement was achieved by transferring laser stability from a remote cryogenic silicon cavity located in Jun Ye‘s laboratory at JILA via a 3.6 km fiber link. This modification resulted in a threefold reduction in instability compared to earlier aluminum ion clocks.
Precision Redefined Through Design Improvements
The research team also redesigned the ion trap to minimize excess micromotion, which refers to tiny unwanted movements that can disrupt timing. Enhancements included utilizing a thicker diamond wafer and modifying gold coatings on the electrodes to correct electrical imbalances. Additionally, the vacuum chamber was reconstructed from titanium, significantly reducing background hydrogen gas by 150 times. This alteration led to a decrease in collisional shifts, enabling the clock to function for days without the need to reload ions.
Researchers further improved measurement accuracy by assessing the ac magnetic field from the radio-frequency trap in a direction-sensitive manner, thereby eliminating uncertainties associated with field orientation. These advancements allow the clock to achieve 19-decimal-place precision in approximately 36 hours, a remarkable improvement over the previous three weeks.
“This platform positions us to explore new clock architectures, such as increasing the number of clock ions and even entangling them, which would further enhance our measurement capabilities,” stated Willa Arthur-Dworschack, a graduate student involved in the project.
The implications of this breakthrough extend beyond mere timekeeping. The newfound precision could redefine the second and open avenues for advancements in Earth science and fundamental physics. This includes investigating whether the constants of nature remain constant, thereby advancing our understanding of the universe. The journey to create the most accurate clock serves not only as a testament to scientific progress but also as a foundation for future explorations in time and space.
