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Lutetium atomic clocks verified at the 19th digit

Lutetium atomic clocks verified at the 19th digit

New Capabilities

Two independent 176Lu+ clocks agree at 5.7 × 10⁻¹⁹, the most precise clock comparison ever measured

2 days ago: Nature publishes lutetium clock verification

Overview

Updated 1 hour ago

The world's most accurate clock would take more than 260 billion years to lose a second. Researchers at the National University of Singapore (NUS) built two of them from the rare-earth metal lutetium and verified they agree to the 19th decimal place — the most precise clock comparison ever performed.

Published in Nature on September 23, the result is four times more accurate than the previous record holder, a calcium-ion clock. It strengthens the case for redefining the SI second, tied to cesium microwave radiation since 1967, using optical clocks in or after 2030. Lutetium is now a leading candidate to anchor that redefinition.

Why it matters

A fourfold leap in timekeeping precision could anchor a redefined second and sharpen GPS, finance, and fundamental physics.

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Key Indicators

5.7 × 10⁻¹⁹
Agreement between the two clocks
Relative frequency difference after 200 hours of averaging, the most precise clock comparison ever performed.
1 × 10⁻¹⁹
Systematic uncertainty
Lowest reported for any optical atomic clock; about four times better than the prior calcium-ion record.
260 billion yrs
Time for the clock to lose one second
Computed from the clock's fractional frequency accuracy of about 1 × 10⁻¹⁹.
4×
Accuracy gain over previous best
Lutetium beats the prior record-holding clock, which used calcium ions, by roughly four times.

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People Involved

Murray Barrett
Murray Barrett
Physicist who led the lutetium clock team at NUS
Led the 10-year project that built and verified the two clocks
 Kyle Arnold
Kyle Arnold
NUS physicist on the lutetium clock team
Part of the group that built and characterized the clocks

Organizations Involved

National University of Singapore
National University of Singapore
Research university
Home of the lutetium optical clock team

NUS's Centre for Quantum Technologies built and verified the two lutetium optical clocks.
Nature
Nature
Scientific journal
Published the peer-reviewed clock results

Nature published the lutetium clock results online on September 23, 2026.

Timeline

December 2025 September 2026

3 events Latest: 2 days ago

  1. Nature publishes lutetium clock verification

    Latest Publication

    Peer-reviewed paper confirms the two ¹⁷⁶Lu⁺ clocks agree at 5.7 × 10⁻¹⁹ after 200 hours of averaging, with total systematic uncertainty near 1 × 10⁻¹⁹.

  2. Results presented at APS DAMOP

    Conference

    Team presents the two-clock comparison at the American Physical Society's Division of Atomic, Molecular and Optical Physics annual meeting, citing 1 × 10⁻¹⁹ systematic uncertainty.

  3. Lutetium clock results posted to arXiv

    Publication

    Team posts preprint 'Optical clocks with accuracy validated at the 19th digit' (arXiv:2512.07346), reporting systematic uncertainties of 1.1 × 10⁻¹⁹ and 1.4 × 10⁻¹⁹ for the two systems.

Scenarios

1

Lutetium chosen to define the redefined second

Possible Resolves by End of 2030

Discussed by: Metrologists at the International Bureau of Weights and Measures (BIPM); Nature news coverage lists lutetium as one of a handful of candidate elements for the 2030 redefinition.

The BIPM consults the community on which optical transition will define the SI second after 2030. Lutetium's verified 10⁻¹⁹ accuracy, room-temperature operation, and low sensitivity to magnetic fields make it a leading candidate alongside strontium and ytterbium lattice clocks. If chosen, the ¹⁷⁶Lu⁺ ¹S₀ ↔ ³D₁ transition would replace cesium-133 microwave radiation as the definition.

2

Miniaturized lutetium clock demonstrated outside the lab

Possible Resolves by End of 2029

Discussed by: Murray Barrett's NUS team, quoted in Nature news about hopes to miniaturize the clock and take it out of the lab.

The NUS team adapts the room-temperature lutetium design into a transportable unit. A portable version would enable chronometric levelling, mapping gravitational potential changes at the millimetre scale for geodesy, civil engineering, and geophysics. Commercial laser components already used in the lab design aid portability.

3

Competing atom surpasses lutetium accuracy

Unlikely Resolves by End of 2028

Discussed by: The broader metrology community; UCLA physicist David Leibrandt notes that accuracy claims require verification by direct clock comparison.

A competing optical clock, using calcium, strontium, ytterbium, or a neutral-atom lattice, reports a lower evaluated uncertainty or a more precise same-species comparison. The NUS lutetium result set the bar about four times better than the previous calcium record, so a challenger would need a major advance to reclaim the lead.

Historical Context

3 moments from history that rhyme with this story — and how they unfolded.

October 1967

Redefinition of the second (1967)

The 13th General Conference on Weights and Measures replaced astronomical timekeeping with atomic time, defining the second by the microwave transition of cesium-133. Previously, the second was tied to Earth's rotation, which drifts by milliseconds per century.

Then

The cesium standard ended reliance on astronomical observations and enabled the GPS, telecommunications, and finance systems built on precise timing.

Now

The 1967 decision set the precedent that metrologists revisit the second's definition as clocks improve — the same process now targeting optical clocks.

Why this matters now

The 2026 lutetium result is the latest step in that redefinition process, which BIPM plans to revisit in or after 2030.

Early 2000s

Optical lattice clock development (2000s)

Researchers at JILA and elsewhere built the first optical lattice clocks using strontium, trapping thousands of atoms in a laser lattice to reach fractional uncertainties below 10⁻¹⁷. These demonstrated that visible-light frequencies could outperform microwave cesium clocks.

Then

Optical lattice clocks overtook cesium standards in accuracy, prompting the push toward an optical definition of the second.

Now

They established that room-temperature, tabletop systems could reach precisions that rival or exceed large national-standard installations.

Why this matters now

Lutetium's single-ion approach now matches lattice-clock accuracy while adding the stability that ion clocks historically lacked, breaking the old accuracy-versus-stability trade-off.

2010s–2020s

Calcium ion optical clock (prior record)

A calcium-ion single clock held the lowest systematic uncertainty among optical standards before lutetium, evaluated below 10⁻¹⁸. Calcium-ion designs were limited mainly by sensitivity to electric fields and blackbody radiation.

Then

The calcium result set the benchmark that other single-ion systems had to match.

Now

It highlighted that single-ion clocks could be exceptionally accurate but struggled to compete with lattice clocks on stability, a gap lutetium now closes with correlation spectroscopy.

Why this matters now

Lutetium's fourfold improvement over the calcium record, combined with stability of 4.8 × 10⁻¹⁶ (τ/s)⁻¹/², directly addresses the weakness that held ion clocks back.

Sources

(9)
+3
Nature arXiv NUS News APS Division of Atomic, Molecular and Optical Physics EurekAlert! The Quantum Insider Science Advances Springer Nature Nature (news)