Atomic Clocks and the Coming Redefinition of the Second
What a clock really is
Any clock needs two parts: something that ticks steadily, and a counter. A pendulum ticks at a rate set by its length, which changes with temperature. An atom ticks at a rate set by physics. Every caesium atom, for example, responds to the same microwave frequency, so a clock locked to that frequency can be copied anywhere. The current international definition of the second is based on caesium. This is a form of quantum sensing that has been quietly running the world for decades.
From microwaves to light
Better clocks come from higher frequencies. Caesium clocks tick at microwave frequencies. Optical clocks lock to atoms or ions excited by visible or near-visible light, which oscillates hundreds of thousands of times faster. More ticks per second means you can slice time more finely. According to the International Bureau of Weights and Measures (BIPM), optical clocks are 10 to 100 times more accurate than microwave clocks, and the best caesium fountains have been surpassed by optical standards with about two orders of magnitude lower systematic uncertainties. In plain terms, the definition of the second is now the limit, not the technology.
The leading candidates
- Strontium atoms held in a lattice of laser light.
- Ytterbium atoms or ions, a close rival.
- Other ions are studied too, and several are already reported to the BIPM as secondary representations of the second.
A Chinese team at USTC was reported to have achieved a strontium clock uncertainty of 9.2 parts in 10 to the 19, and the researchers said this meets the accuracy requirement set for redefining the second. Treat single-lab figures as reported results, not final rulings.
The timeline, as the BIPM describes it
| Step | Date |
|---|---|
| General Conference (CGPM) reviews progress | 2026 |
| Consultative Committee evaluates criteria and finalizes a proposal | 2028 to 2029 |
| CGPM decides on a new definition and implementation date, if consensus and mandatory criteria are met | 2030 |
The BIPM lists eight mandatory criteria and six ancillary conditions. These include an immediate accuracy gain of 10 to 100 times, continuity with the caesium definition, and acceptance by national metrology institutes. Options being considered are a single optical transition or a weighted average of several. The BIPM says the change will not disrupt everyday timekeeping.
The hidden problem: comparing clocks
A clock is only useful if you can compare it with others. Satellite time transfer cannot yet support comparisons at optical precision, so the BIPM points to optical fibre links, which so far have been demonstrated over roughly 1000 km. This is a big reason why the redefinition is a multi-year engineering effort and not just a vote.
Why ordinary people should care
You will not see the new second on your phone. But better time underpins many things you rely on: synchronized cell networks, power grid monitoring, financial timestamps and satellite navigation. When clocks improve, the whole stack can improve with them. Better clocks also act as sensors in their own right. Because time runs very slightly differently at different heights, ultra-precise clocks can in principle detect tiny gravity differences, linking this topic to gravity sensing.
Smaller clocks for the field
The lab record-setters fill rooms. Another track is shrinking clocks for vehicles. The UK defence science lab Dstl was reported to complete trials of next-generation atomic clock technology in February 2026, including devices aimed at underwater use with the Royal Navy, as a fallback for satellite timing. The UK government announced the trial on February 18, 2026, with a follow-up trial planned for 2027. Holdover, the ability of a clock to keep good time when GPS is lost, is exactly what GPS-free navigation needs.
Where this fits in the bigger picture
Atomic clocks are the oldest and most proven quantum technology, which is part of why sensing is the nearest-term story. The next decade is about making them smaller, tougher and networked. None of this relates to any crypto asset, and nothing here is financial advice.
Sources and further reading
- BIPM: FAQ on the redefinition of the second
- ScienceAlert: new clock could redefine the second
- GOV.UK: trial speeds up next generation of atomic clocks
- Quantum Computing Report: Dstl atomic clock trials
- GEANT: Time and Frequency Pathfinder Study
Reported as of 2026-10-09. Many test results below are company reported and not independently confirmed. Check primary documents before relying on any figure. This site is educational and is not financial advice. The QNT memecoin is independent and is not linked to Quantinuum Ltd or any company, lab or government named here.
Frequently asked questions
Why redefine the second?
Optical clocks have become more accurate than the caesium clocks that define it, so the definition now limits accuracy, according to the BIPM.
When could the new second arrive?
The BIPM roadmap points to a decision at the 2030 General Conference at the earliest, and only if mandatory criteria are met.
Will my phone or watch change?
No. The BIPM says the redefinition will not disrupt everyday timekeeping.
Are atomic clocks quantum technology?
Yes. They are among the oldest quantum technologies, using the fixed energy levels of atoms as a reference.
Keep reading
- Quantum Sensing Explained
What is quantum sensing? Learn how quantum sensors measure time, motion, gravity and magnetic fields with great precision, and where they are used. - Quantum Navigation Without GPS: Flight Tests and Defense Interest
How magnetic maps and quantum sensors can back up GPS, what the reported 2025 and 2026 flight tests showed, and what is still unproven. - Why Quantum Sensing May Be the Nearest-Term Quantum Technology
Quantum sensors do not need thousands of perfect qubits. Here is why sensing, timing and navigation are reaching real customers before big quantum computers. - Magnetometers, Gravimeters and NV Diamonds Explained
A tour of three families of quantum field sensors: atomic vapor magnetometers, diamond NV centers and cold atom gravity sensors, plus who is building them.
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