World's most accurate atomic clock redefines how me measure second

The National Institute of Standards and Technology (NIST) has developed the world’s most accurate aluminum ion-based optical atomic clock, setting a new benchmark by measuring a second to its 19th decimal place. This clock is 41% more accurate and 2.6 times more stable than the previous record holder, reflecting two decades of refinement. Unlike traditional cesium atomic clocks, this device uses a single aluminum ion known for its exceptionally steady high-frequency vibrations, paired with a magnesium ion in a “buddy system” through quantum logic spectroscopy. The magnesium ion helps cool the aluminum ion and facilitates precise measurement of its “ticks.” Achieving this unprecedented precision involved overcoming several technical challenges, including redesigning the ion trap to minimize unwanted ion motion and constructing a vacuum chamber from titanium to drastically reduce hydrogen interference. Additionally, the clock benefits from an ultrastable laser developed at JILA, whose beam travels over two miles via fiber optics to NIST, enhancing the clock’s stability and reducing measurement time from weeks