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Atomic clocks

Clocks that keep time by the vibration of atoms, used in navigation satellites, telecoms and precision measurement.

The United States leads atomic clocks research, with 38.7% of the 10% most cited papers published 2021–2025; China is second with 19.9%.

US
FirstUnited States38.7%
CN
SecondChina19.9%
1.9×lead, by share of the 10% most cited papers, 2021–2025

Standings

1USUnited States38.7%2CNChina19.9%3DEGermany11.5%4–6GBUnited Kingdom4.7%4–6JPJapan4.7%4–6AUAustralia4.2%7–8FRFrance3.5%7–8ATAustria2.9%9–16BEBelgium0.8%9–16KRSouth Korea0.8%

Share of the 10% most cited papers, 2021–2025; 127 papers. Source: OpenAlex, pulled 18 October 2026. Method

Year by year

About 25 papers a year. Single-year moves are noise.
0204060% 20212022202320242025 United States 39.9%China 19.3%Australia 9.9%Germany 7.6%United Kingdom 2.6%Japan 0.5%

Share of the 10% most cited papers published in each year. Source: OpenAlex, pulled 18 October 2026. Method

Inside the field

Always the top 10%Pilot

Each paper sorted into one sub-area by an AI model reading its title and abstract, then credited as usual. On 200 hand-labelled papers it chose the same sub-area, or a defensible second, 92% of the time.

Sub-areaPapersFirstSecondThird
Optical lattice and trapped-ion clock performance34USUnited States61.2%CNChina14.4%DEGermany9.4%
Time and frequency transfer, and GNSS satellite clocks20CNChina37.5%USUnited States16.3%DEGermany11.5%
Compact, transportable and space-borne clocks18USUnited States31.6%CNChina28.7%DEGermany7.9%
Thorium-229 and other nuclear clocks16USUnited States35.7%ATAustria22.0%DEGermany19.1%
Ultrastable lasers and optical cavities14USUnited States42.0%CNChina27.7%ILIsrael7.1%
Tests of fundamental physics with clocks12DEGermany34.8%USUnited States30.6%GBUnited Kingdom16.1%

Share of each sub-area's papers in the top 10%. Source: OpenAlex, pulled 18 October 2026. Method

Earlier and recent

Small sample: 59 papers in one period.

The same top 10%, split into 2021–2023 and 2024–2025.

FallingRising2021–20232024–2025Change
USUnited States 36.1%41.6%+5.5 pts
CNChina 19.3%20.6%+1.4 pts
DEGermany 14.8%7.6%−7.2 pts
GBUnited Kingdom 5.0%4.4%−0.6 pts
JPJapan 5.8%3.5%−2.3 pts
AUAustralia 3.3%5.3%+2.1 pts
FRFrance 5.5%1.3%−4.2 pts
ATAustria 1.6%4.4%+2.8 pts

Greyed rows rest on fewer than five papers of credit in one period.

Share of the 10% most cited papers: 68 papers in 2021–2023, 59 in 2024–2025. Source: OpenAlex, pulled 18 October 2026. Method

2026 so far: a different count

Not the most cited papers: every 2026 paper matched so far (223), and a paper counts in full for each country on it. This year's papers are too new to rank by citations, so these shares cannot be compared with the ones above.

  1. CNChina44.8%of 2026 papers have an author here
  2. USUnited States14.3%of 2026 papers have an author here
  3. DEGermany7.2%of 2026 papers have an author here
  4. JPJapan4.0%of 2026 papers have an author here
  5. AUAustralia3.1%of 2026 papers have an author here

With home citations removed

Home bias removed

Removes only the home citations above what the country's share of the field predicts. This is the fair test.

All citationsBias removedAll citationsBias removed
USUnited States 38.7%39.0%
CNChina 19.9%16.9%
DEGermany 11.5%12.8%
GBUnited Kingdom 4.7%4.7%
JPJapan 4.7%4.7%
AUAustralia 4.2%4.7%

Every home citation removed

Removes all citations from a paper's own countries. A country that writes most of a field loses most, whatever its habits.

All citationsForeign onlyAll citationsForeign only
USUnited States 38.7%41.4%
CNChina 19.9%6.3%
DEGermany 11.5%13.3%
GBUnited Kingdom 4.7%4.7%
JPJapan 4.7%6.2%
AUAustralia 4.2%7.0%

Share of the 10% most cited papers, 2021–2025; 127 papers in each version; both panels on the same scale. Source: OpenAlex, pulled 18 October 2026. Method

Who cites the top papers

How much more often a country's top papers are cited from home than its size predicts. Expected is the country's share of all papers in the field; the bar is the excess, in percentage points. Home citers include authors citing their own earlier work.

HomeExpectedExcess
USUnited States 38.0%17.4%+20.6
CNChina 74.3%42.2%+32.1
DEGermany 39.5%9.9%+29.6
GBUnited Kingdom 40.5%4.1%+36.4
JPJapan 44.1%4.1%+40.0
AUAustralia 54.0%3.4%+50.6
FRFrance 46.6%5.4%+41.2
ATAustria 41.1%2.6%+38.5

Every paper in the top 10%, counted once per citing paper. Source: OpenAlex, pulled 18 October 2026. Method

Behind the share

Institutions with the most credit

  1. 1USNational Institute of Standards and TechnologyGovernment lab10.0%
  2. 2USUniversity of Colorado Boulder5.1%
  3. 3DEPhysikalisch-Technische BundesanstaltGovernment lab4.9%
  4. 4USJoint Institute for Laboratory AstrophysicsResearch facility4.6%
  5. 5GBNational Physical LaboratoryResearch facility2.5%
  6. 6CNChinese Academy of SciencesGovernment lab2.3%
  7. 7CNPeking University1.9%
  8. 8ATTU Wien1.7%
  9. 9USUniversity of Wisconsin–Madison1.7%
  10. 10AUThe University of Adelaide1.6%

Share of the top 10%. Institutions across all 45 technologies

Who does the work

SectorAllUSCNDE
Universities45.1%
50.2%
54.4%
15.9%
Research facilities27.0%
19.4%
27.3%
24.9%
Government labs21.2%
26.1%
13.3%
43.9%
Non-profits2.5%
2.0%
0%
11.0%

Share of credit by type of institution, overall and for the three leading countries.

Across borders

33.1% of the top 10% have authors in more than one country.

  1. DEUSGermany with United States12
  2. GBUSUnited Kingdom with United States9
  3. ATDEAustria with Germany8
  4. JPUSJapan with United States7
  5. ATUSAustria with United States6

Most frequent pairings, by number of shared papers.

The papers behind the numbers

The five most cited papers this definition catches. If one looks out of place, the definition needs work.

  1. 446citations
  2. 389citations
  3. 210citations
  4. 199citations
  5. 194citations

More in quantum

The most technologically advanced countries, and is China ahead of the US?

How this technology is defined

A paper counts if its title or abstract matches the search below. Articles in core journals and proceedings only; retracted papers are excluded.

"atomic clock" OR "optical clock" OR "optical lattice clock" OR "frequency standard" OR "atomic fountain" OR "ion clock" OR "nuclear clock" OR "clock transition" OR "time and frequency transfer"

and its main topic in OpenAlex is one of: Advanced Frequency and Time Standards; Cold Atom Physics and Bose-Einstein Condensates; Quantum optics and atomic interactions; Atomic and Molecular Physics; Atomic and Subatomic Physics Research; Network Time Synchronization Technologies; GNSS positioning and interference. The topic check removes papers that only mention the technology.

Papers matched, 2021–2025
1,257
In the top 10%
127
In the top 1%
16
Countries with credit
27
Credit with no known country
4.5%
Every one of the 166 most cited papers was checked for relevance; 10 were left out as not about atomic clocks

The most cited of those left out:

  • Laser cooling of antihydrogen atoms84 citations
  • Continuous operation of a coherent 3,000-qubit system56 citations
  • Navigation Using Doppler Shift From LEO Constellations and INS Data40 citations
  • Coherence limits in lattice atom interferometry at the one-minute scale38 citations
  • Ground-State g Factor of Highly Charged Th229 Ions: An Access to the M1 Transition Probability between the Isomeric and Ground Nuclear States31 citations
  • Collective Radiation of a Cascaded Quantum System: From Timed Dicke States to Inverted Ensembles31 citations
  • Hamiltonian engineering of collective XYZ spin models in an optical cavity21 citations
  • Nanosecond-Level Resilient GNSS-Based Time Synchronization in Telecommunication Networks Through WR-PTP HA17 citations
  • Resilient satellite-based PNT system design and key technologies15 citations
  • Atom interferometry in an Einstein Elevator11 citations

Definition version 0.5, pilot. It is a plain text file: copy it, change it, rerun it.

Read the method