US lab sets world record for most accurate clock, 41% more efficient device offers 2.6% more stability than other ion clock

The newly modified ion trap for NIST’s aluminum ion clock, with an inset showing a CCD image of the aluminum-magnesium ion pair. The circle shows the position of the aluminum ion, which is dark to the camera as it can only be read out using quantum logic spectroscopy via the magnesium ion. Credit: NIST

In a groundbreaking achievement, researchers at the National Institute of Standards and Technology (NIST) have unveiled the most accurate clock in the world, an advanced atomic clock that utilizes a trapped aluminum ion.

This remarkable device is part of the latest generation of optical atomic clocks and boasts an astonishing timekeeping precision of 19 decimal places.

Optical clocks are assessed based on two critical factors: accuracy, which measures how closely a clock aligns with the ideal "true" time, and stability, which gauges the clock's efficiency in measuring time. The new aluminum ion clock has surpassed its predecessor by an impressive 41% in accuracy and is 2.6 times more stable than any other ion clock currently in existence.

Achieving this level of precision has required meticulous enhancements to every component of the clock, from the laser to the trap and vacuum chamber.

Exciting work on most accurate clock

The research team's findings were published in the prestigious journal Physical Review Letters.

“It’s exciting to work on the most accurate clock ever,” said Mason Marshall, a NIST researcher and the lead author of the study. “At NIST, we have the opportunity to pursue long-term precision measurement projects that can advance the field of physics and deepen our understanding of the universe.”

The aluminum ion is an exceptional timekeeper, exhibiting a remarkably steady and high-frequency "ticking" rate.

Aluminum ion's ticks are more stable than those of cesium

According to David Hume, the NIST physicist leading the project, the aluminum ion's ticks are more stable than those of cesium, which currently defines the second in scientific terms. Additionally, the aluminum ion is less sensitive to environmental factors such as temperature and magnetic fields.

However, working with aluminum ions presents challenges. Marshall explained that aluminum is difficult to probe and cool with lasers, both essential techniques for atomic clocks. To overcome this, the research team paired the aluminum ion with magnesium, which, while lacking the exquisite ticking properties of aluminum, can be easily controlled with lasers. This innovative approach, known as quantum logic spectroscopy, allows the magnesium ion to cool the aluminum ion and synchronize their movements, enabling the clock's state to be read through the magnesium ion's motion.

NIST physicist David Hume holds the newly modified ion trap for the aluminum ion clock. By modifying the trap, the aluminum ion and its magnesium ion partner were able to “tick” unperturbed. Credit: R. Jacobson/NIST

“It’s a big, complex challenge because every part of the clock’s design affects its performance,” said Daniel Rodriguez Castillo, a graduate student involved in the project.

One significant hurdle was the design of the ion trap, which was causing tiny movements known as excess micromotion that compromised the clock's accuracy.

The team redesigned the trap, placing it on a thicker diamond wafer and modifying the gold coatings on the electrodes to correct electrical imbalances that disturbed the ions. These refinements slowed the ions' motion, allowing them to "tick" without interference.

The vacuum system housing the trap also posed challenges. Traditional steel vacuum chambers allowed hydrogen to diffuse, which interfered with the ions' operation. To address this, the team constructed a new vacuum chamber from titanium, reducing hydrogen gas interference by 150 times. This upgrade enabled the clock to run for days without needing to reload the ions, a significant improvement over the previous requirement of reloading every 30 minutes.

A more stable laser was also essential for probing the ions and counting their ticks. The previous version of the clock required weeks of operation to average out quantum fluctuations caused by its laser. To enhance stability, the team collaborated with Jun Ye at NIST's JILA, who operates one of the world's most stable lasers. By sending the ultrastable laser beam 3.6 kilometers (over 2 miles) to NIST, the researchers were able to synchronize the aluminum ion clock with Ye's laser, significantly improving its performance.

With these advancements, the aluminum ion clock is poised to contribute to the international effort to redefine the second with unprecedented accuracy, paving the way for new scientific and technological breakthroughs. The upgrades also enhance its potential as a quantum logic testbed, allowing researchers to explore new concepts in quantum physics and develop tools for quantum technology.

“By reducing the averaging time from weeks to days, this clock can facilitate new measurements of Earth’s geodesy and investigate physics beyond the Standard Model,” Arthur-Dworschack noted. “With this platform, we're ready to explore new clock architectures, scale up the number of clock ions, and even entangle them, further enhancing our measurement capabilities.”

As the world of precision timekeeping continues to evolve, NIST's latest work marks a significant milestone in our quest to understand the fundamental nature of time and the universe.