The Most Accurate Clock Ever Built: NIST’s Quantum Logic Breakthrough

July 17, 2025

In a remarkable leap for precision timekeeping, scientists at the National Institute of Standards and Technology (NIST) have built the world’s most accurate clock — a quantum logic atomic clock based on an aluminum ion. This record-setting instrument can now measure time to an unprecedented level of 19 decimal places.

A 20-Year Journey Toward Perfect Timing

The achievement stems from two decades of innovation and refinement. NIST’s aluminum ion clock — now the most accurate in the world — uses a technique known as quantum logic spectroscopy, which pairs an aluminum ion with a magnesium ion. The magnesium ion acts as a “helper,” enabling researchers to cool and read the elusive aluminum ion with incredible precision.

(From left to right) Mason Marshall, David Hume, Willa Arthur-Dworschack, and Daniel Rodriguez Castillo in front of the NIST aluminum ion clock. With its recent improvements, the clock could help redefine the second.Credit: R. Jacobson/NIST

This latest version isn’t just a little better — it’s 41% more accurate than the previous record-holder and 2.6 times more stable than any other ion-based clock. That stability is crucial for applications ranging from GPS synchronization to probing the very foundations of physics.

Understanding Accuracy and Stability

Atomic clocks are judged on two main fronts:

• Accuracy — how closely the clock approaches “true” time, and
• Stability — how reliably it measures time over a given period.

The aluminum ion “ticks” with incredible precision. It even outperforms the cesium-based clocks that currently define the official length of a second. But aluminum ions are notoriously hard to control. That’s where magnesium comes in — easy to manipulate with lasers, it helps steady and read out the clock’s state.

NIST physicist David Hume holds the newly modified ion trap. The aluminum and magnesium ion pair tick in sync thanks to a careful redesign.Credit: R. Jacobson/NIST

 Overcoming Engineering Challenges

Getting the clock to this level of performance meant redesigning multiple components, including:

• The Ion Trap: The aluminum and magnesium ions are suspended in a trap that originally caused tiny shifts known as excess micromotion. These fluctuations undermined precision. The NIST team resolved this by upgrading the trap structure — using a thicker diamond wafer and enhanced gold electrode coatings — which minimized unwanted electrical imbalances.

A closer look at the newly modified ion trap. The circle shows the location of the aluminum ion, which is dark because it’s read indirectly through the magnesium ion.Credit: NIST

• The Vacuum Chamber: Standard steel vacuum chambers slowly leak hydrogen, disturbing the ion pair. The team rebuilt the chamber in titanium, reducing background gas by a factor of 150. This improvement stretched the clock’s continuous runtime from 30 minutes to several days.
• The Laser System: Precision measurements depend on a stable laser. Partnering with Jun Ye’s lab at JILA, the team linked their system via fiber optics to one of the most stable lasers in the world. This allowed them to extend ion probing time from 150 milliseconds to a full second — a game-changer for clock stability.

Daniel Rodriguez Castillo, Willa Arthur-Dworschack, and Mason Marshall working on the aluminum ion clock. Their work has led to a new world record in timing accuracy. Credit: R. Jacobson/NIST

Why It Matters: Redefining the Second and Beyond

This new benchmark pushes the world closer to redefining the second — the foundation of our entire system of timekeeping — with optical standards like the aluminum ion clock.

But the implications don’t stop there.

With this clock, scientists can now explore frontier questions in physics, including:

• The constancy of nature’s fundamental constants
• Precision geodesy (measuring Earth’s shape and gravity)
• Testing the limits of quantum mechanics and general relativity

“It’s a complex puzzle where every piece affects the final picture,” said graduate student Daniel Rodriguez Castillo. “But now we have a platform that can unlock entirely new scientific directions.”

Looking Ahead

As the clock continues to evolve, researchers are already planning to scale it up — entangling multiple ions and pushing even further into the realm of quantum precision.

“This platform gives us a foundation to build more advanced clocks, test new ideas in quantum logic, and explore how nature really works at the deepest levels,” said Willa Arthur-Dworschack.

Source: https://www.nist.gov/news-events/news/2025/07/nist-ion-clock-sets-new-record-most-accurate-clock-world

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