Atomic clock (English Wikipedia)

"Notice Advisory to Navstar Users (NANU) 2012034". GPS Operations Center. 30 May 2012. Archived from the original on 8 April 2013. Retrieved 2 July 2012.

airforce-technology.com (Global: 4,662^nd place; English: 3,786^th place)

"DARPA to launch programme for creating optical atomic clocks". Airforce Technology. 21 January 2022. Retrieved 15 February 2022.

allanstime.com (Global: low place; English: low place)

Allan, David W. (1997). "The Science of Timekeeping" (PDF). Application Note (1289). Hewlett Packard. Archived (PDF) from the original on 25 October 2012.

aps.org (Global: 1,503^rd place; English: 1,378^th place)

journals.aps.org

Brewer, S. M.; Chen, J.-S.; Hankin, A. M.; Clements, E. R.; Chou, C. W.; Wineland, D. J.; Hume, D. B.; Leibrandt, D. R. (15 July 2019). "Al+27 Quantum-Logic Clock with a Systematic Uncertainty below 10⁻¹⁸". Physical Review Letters. 123 (3) 033201. arXiv:1902.07694. doi:10.1103/physrevlett.123.033201. ISSN 0031-9007. PMID 31386450. S2CID 119075546.

physics.aps.org

Thirolf, Peter (29 April 2024). "Shedding Light on the Thorium-229 Nuclear Clock Isomer". Physics. Vol. 17. doi:10.1103/Physics.17.71.

link.aps.org

Koller, S. B.; Grotti, J.; Vogt, St.; Al-Masoudi, A.; Dörscher, S.; Häfner, S.; Sterr, U.; Lisdat, Ch. (13 February 2017). "Transportable Optical Lattice Clock with 7×10⁻¹⁷ Uncertainty". Physical Review Letters. 118 (7) 073601. arXiv:1609.06183. doi:10.1103/PhysRevLett.118.073601. ISSN 0031-9007. PMID 28256845. S2CID 40822816.

archives-ouvertes.fr (Global: 1,031^st place; English: 879^th place)

hal.archives-ouvertes.fr

Dupays, Arnaud; Beswick, Alberto; Lepetit, Bruno; Rizzo, Carlo (August 2003). "Proton Zemach radius from measurements of the hyperfine splitting of hydrogen and muonic hydrogen" (PDF). Physical Review A. 68 (5) 052503. arXiv:quant-ph/0308136. Bibcode:2003PhRvA..68e2503D. doi:10.1103/PhysRevA.68.052503. S2CID 3957861. Archived (PDF) from the original on 14 January 2019. Retrieved 26 September 2016.

arxiv.org (Global: 69^th place; English: 59^th place)

Lodewyck, Jérôme (16 September 2019). "On a definition of the SI second with a set of optical clock transitions". Metrologia. 56 (5) 055009. arXiv:1911.05551. Bibcode:2019Metro..56e5009L. doi:10.1088/1681-7575/ab3a82. ISSN 0026-1394. S2CID 202129810.
Nicholson, T. L.; Campbell, S. L.; Hutson, R. B.; Marti, G. E.; Bloom, B. J.; McNally, R. L.; Zhang, W.; Barrett, M. D.; Safronova, M. S.; Strouse, G. F.; Tew, W. L. (21 April 2015). "Systematic evaluation of an atomic clock at 2×10⁻¹⁸ total uncertainty". Nature Communications. 6 (1) 6896. arXiv:1412.8261. Bibcode:2015NatCo...6.6896N. doi:10.1038/ncomms7896. ISSN 2041-1723. PMC 4411304. PMID 25898253.
Brewer, S. M.; Chen, J.-S.; Hankin, A. M.; Clements, E. R.; Chou, C. W.; Wineland, D. J.; Hume, D. B.; Leibrandt, D. R. (15 July 2019). "Al+27 Quantum-Logic Clock with a Systematic Uncertainty below 10⁻¹⁸". Physical Review Letters. 123 (3) 033201. arXiv:1902.07694. doi:10.1103/physrevlett.123.033201. ISSN 0031-9007. PMID 31386450. S2CID 119075546.
Bothwell, Tobias; Kennedy, Colin J.; Aeppli, Alexander; Kedar, Dhruv; Robinson, John M.; Oelker, Eric; Staron, Alexander; Ye, Jun (16 February 2022). "Resolving the gravitational redshift across a millimetre-scale atomic sample". Nature. 602 (7897): 420–424. arXiv:2109.12238. Bibcode:2022Natur.602..420B. doi:10.1038/s41586-021-04349-7. ISSN 0028-0836. PMID 35173346. S2CID 246902611.
Dimarcq, Noel; Gertsvolf, Marina; Mileti, Gaetano; Bize, Sebastien; Oates, Christopher; Peik, Ekkehard; Calonico, Davide; Ido, Tetsuya; Tavella, Patrizia; Meynadier, Frédéric (2024). "Roadmap towards the redefinition of the second". Metrologia. 61 (1): 012001. arXiv:2307.14141. Bibcode:2024Metro..61a2001D. doi:10.1088/1681-7575/ad17d2.
Poli, N (2014). "Optical atomic clocks". La Rivista del Nuovo Cimento. 36 (12): 555. arXiv:1401.2378. Bibcode:2013NCimR..36..555P. doi:10.1393/ncr/i2013-10095-x. S2CID 118430700.
Ludlow, A. D.; Boyd, M. M.; Ye, Jun; Peik, E.; Schmidt, P. O. (26 June 2015). "Optical atomic clocks". Reviews of Modern Physics. 87 (2): 637–701. arXiv:1407.3493. Bibcode:2015RvMP...87..637L. doi:10.1103/RevModPhys.87.637. S2CID 119116973.
Westergaard, P. G.; Lodewyck, J.; Lemonde, P. (March 2010). "Minimizing the Dick effect in an optical lattice clock". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 57 (3): 623–628. arXiv:0909.0909. Bibcode:2010ITUFF..57..623W. doi:10.1109/TUFFC.2010.1457. PMID 20211780. S2CID 10581032.
Pottie, Paul-Eric; Grosche, Gesine (19 August 2016). "A clock network for geodesy and fundamental science". Nature Communications. 7 12443. arXiv:1511.07735. Bibcode:2016NatCo...712443L. doi:10.1038/ncomms12443. PMC 4980484. PMID 27503795.
Campbell, C.; Radnaev, A.G.; Kuzmich, A.; Dzuba, V.A.; Flambaum, V.V.; Derevianko, A. (2012). "A single ion nuclear clock for metrology at the 19th decimal place". Phys. Rev. Lett. 108 (12) 120802. arXiv:1110.2490. Bibcode:2012PhRvL.108l0802C. doi:10.1103/PhysRevLett.108.120802. PMID 22540568. S2CID 40863227.
von der Wense, Lars; Seiferle, Benedict; Laatiaoui, Mustapha; Neumayr, Jürgen B.; Maier, Hans-Jörg; Wirth, Hans-Friedrich; Mokry, Christoph; Runke, Jörg; Eberhardt, Klaus; Düllmann, Christoph E.; Trautmann, Norbert G.; Thirolf, Peter G. (5 May 2016). "Direct detection of the ²²⁹Th nuclear clock transition". Nature. 533 (7601): 47–51. arXiv:1710.11398. Bibcode:2016Natur.533...47V. doi:10.1038/nature17669. PMID 27147026. S2CID 205248786.
Thielking, J.; Okhapkin, M.V.; Glowacki, P.; Meier, D.M.; von der Wense, L.; Seiferle, B.; Düllmann, C.E.; Thirolf, P.G.; Peik, E. (2018). "Laser spectroscopic characterization of the nuclear-clock isomer ^229mTh". Nature. 556 (7701): 321–325. arXiv:1709.05325. Bibcode:2018Natur.556..321T. doi:10.1038/s41586-018-0011-8. PMID 29670266. S2CID 4990345.
Masuda, T.; Yoshimi, A.; Fujieda, A.; Fujimoto, H.; Haba, H.; Hara, H.; Hiraki, T.; Kaino, H.; Kasamatsu, Y.; Kitao, S.; Konashi, K.; Miyamoto, Y.; Okai, K.; Okubo, S.; Sasao, N.; Seto, M.; Schumm, T.; Shigekawa, Y.; Suzuki, K.; Stellmer, S.; Tamasaku, K.; Uetake, S.; Watanabe, M.; Watanabe, T.; Yasuda, Y.; Yamaguchi, A.; Yoda, Y.; Yokokita, T.; Yoshimura, M.; Yoshimura, K. (12 September 2019). "X-ray pumping of the ²²⁹Th nuclear clock isomer". Nature. 573 (7773): 238–242. arXiv:1902.04823. Bibcode:2019Natur.573..238M. doi:10.1038/s41586-019-1542-3. PMID 31511686. S2CID 119083861.
Seiferle, B.; von der Wense, L.; Bilous, P.V.; Amersdorffer, I.; Lemell, C.; Libisch, F.; Stellmer, S.; Schumm, T.; Düllmann, C.E.; Pálffy, A.; Thirolf, P.G. (12 September 2019). "Energy of the ²²⁹Th nuclear clock transition". Nature. 573 (7773): 243–246. arXiv:1905.06308. Bibcode:2019Natur.573..243S. doi:10.1038/s41586-019-1533-4. PMID 31511684. S2CID 155090121.
Elwell, R.; Schneider, Christian; Jeet, Justin; Terhune, J. E. S.; Morgan, H. W. T.; Alexandrova, A. N.; Tran Tan, Hoang Bao; Derevianko, Andrei; Hudson, Eric R. (2 July 2024). "Laser excitation of the ²²⁹Th nuclear isomeric transition in a solid-state host". Physical Review Letters. 133 (1) 013201. arXiv:2404.12311. doi:10.1103/PhysRevLett.133.013201. PMID 39042795. a narrow, laser-linewidth-limited spectral feature at 148.38219(4)_stat(20)_sys nm (2020407.3(5)_stat(30)_sys GHz) that decays with a lifetime of 568(13)_stat(20)_sys s. This feature is assigned to the excitation of the ²²⁹Th nuclear isomeric state, whose energy is found to be 8.355733(2)_stat(10)</sys> eV in ²²⁹Th:LiSrAlF₆.
Zhang, Chuankun; Ooi, Tian; Higgins, Jacob S.; Doyle, Jack F.; von der Wense, Lars; Beeks, Kjeld; Leitner, Adrian; Kazakov, Georgy; Li, Peng; Thirolf, Peter G.; Schumm, Thorsten; Ye, Jun (4 September 2024). "Frequency ratio of the ^229mTh nuclear isomeric transition and the ⁸⁷Sr atomic clock". Nature. 633 (8028): 63–70. arXiv:2406.18719. Bibcode:2024Natur.633...63Z. doi:10.1038/s41586-024-07839-6. PMID 39232152. The transition frequency between the $I = 5/2$ ground state and the $I = 3/2$ excited state is determined as: $𝜈Th = .mw-parser-output .sfrac{white-space:nowrap}.mw-parser-output .sfrac.tion,.mw-parser-output .sfrac .tion{display:inline-block;vertical-align:-0.5em;font-size:85%;text-align:center}.mw-parser-output .sfrac .num{display:block;line-height:1em;margin:0.0em 0.1em;border-bottom:1px solid}.mw-parser-output .sfrac .den{display:block;line-height:1em;margin:0.1em 0.1em}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}⁠1/6⁠ (𝜈a + 2𝜈b + 2𝜈c + 𝜈d) = 2020407384335(2) kHz$ .
Seiferle, Benedict; von der Wense, Lars; Thirolf, Peter G. (2017). "Lifetime measurement of the ²²⁹Th nuclear isomer". Physical Review Letters. 118 (4) 042501. arXiv:1801.05205. Bibcode:2017PhRvL.118d2501S. doi:10.1103/PhysRevLett.118.042501. PMID 28186791. S2CID 37518294. A half-life of 7±1 μs has been measured
Dupays, Arnaud; Beswick, Alberto; Lepetit, Bruno; Rizzo, Carlo (August 2003). "Proton Zemach radius from measurements of the hyperfine splitting of hydrogen and muonic hydrogen" (PDF). Physical Review A. 68 (5) 052503. arXiv:quant-ph/0308136. Bibcode:2003PhRvA..68e2503D. doi:10.1103/PhysRevA.68.052503. S2CID 3957861. Archived (PDF) from the original on 14 January 2019. Retrieved 26 September 2016.
Brewer, S.; Chen, J.-S.; Hankin, A.; Clements, E. (15 July 2019). "²⁷Al⁺ Quantum-Logic Clock with a Systematic Uncertainty below 10⁻¹⁸". Physical Review Letters. 123 (3) 033201. arXiv:1902.07694. Bibcode:2019PhRvL.123c3201B. doi:10.1103/PhysRevLett.123.033201. PMID 31386450. S2CID 119075546.
Huntemann, N.; Sanner, C.; Lipphardt, B.; Tamm, Chr. (8 February 2016). "Single-Ion Atomic Clock with 3×10⁻¹⁸ Systematic Uncertainty". Physical Review Letters. 116 (6) 063001. arXiv:1602.03908. Bibcode:2016PhRvL.116f3001H. doi:10.1103/PhysRevLett.116.063001. PMID 26918984. S2CID 19870627.
Leute, J.; Huntemann, N.; Lipphardt, B.; Tamm, Christian (3 February 2016). "Frequency Comparison of ¹⁷¹Yb⁺ Ion Optical Clocks at PTB and NPL via GPS PPP". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 63 (7): 981–985. arXiv:1507.04754. doi:10.1109/TUFFC.2016.2524988. PMID 26863657. S2CID 20466105.
Bothwell, Tobias; Kennedy, Colin J.; Aeppli, Alexander; Kedar, Dhruv; Robinson, John M.; Oelker, Eric; Staron, Alexander; Ye, Jun (2022). "Resolving the gravitational redshift across a millimetre-scale atomic sample". Nature. 602 (7897): 420–424. arXiv:2109.12238. Bibcode:2022Natur.602..420B. doi:10.1038/s41586-021-04349-7. PMID 35173346. S2CID 237940816.
Koller, S. B.; Grotti, J.; Vogt, St.; Al-Masoudi, A.; Dörscher, S.; Häfner, S.; Sterr, U.; Lisdat, Ch. (13 February 2017). "Transportable Optical Lattice Clock with 7×10⁻¹⁷ Uncertainty". Physical Review Letters. 118 (7) 073601. arXiv:1609.06183. doi:10.1103/PhysRevLett.118.073601. ISSN 0031-9007. PMID 28256845. S2CID 40822816.

bbc.co.uk (Global: 8^th place; English: 10^th place)

"China GPS rival Beidou starts offering navigation data". BBC. 27 December 2011. Archived from the original on 3 February 2012. Retrieved 22 June 2018.
"China's Beidou GPS-substitute opens to public in Asia". BBC. 27 December 2012. Archived from the original on 27 December 2012. Retrieved 27 December 2012.

beidou.gov.cn (Global: low place; English: low place)

interact.beidou.gov.cn

China Satellite Navigation Office, Version 2.0, December 2013^{[permanent dead link]}

bipm.org (Global: 641^st place; English: 955^th place)

bipm.org

"Roadmap to the redefinition of the second". Retrieved 17 November 2025.
International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), ISBN 92-822-2213-6, archived (PDF) from the original on 4 June 2021, retrieved 16 December 2021
"Mise en pratique for the definition of the second in the SI" (PDF). Bureau International Poids et Mesures. Consultative Committee for Time and Frequency. 20 May 2019.
"Consultative Committee for Units (CCU) Report of the 25th meeting (21-23 September 2021) to the International Committee for Weights and Measures".
"Unit of time (second)". SI Brochure. BIPM. 2014 [2006]. Archived from the original on 19 November 2011. Retrieved 23 June 2015.
"⁸⁷Rubidium BIPM document" (PDF). Archived (PDF) from the original on 23 September 2015. Retrieved 22 June 2015.
"⁸⁷Strontium BIPM document" (PDF). Archived (PDF) from the original on 4 March 2016. Retrieved 25 June 2015.
"²⁷Aluminum ion BIPM document". Archived from the original on 2 August 2022. Retrieved 9 December 2022.
"¹⁷¹Ytterbium 171 ion (642 THz) BIPM document". Archived from the original on 2 August 2022. Retrieved 9 December 2022.
"¹⁷¹Ytterbium 171 ion (688 THz) BIPM document". Archived from the original on 2 August 2022. Retrieved 9 December 2022.

webtai.bipm.org

Explanatory Supplement of BIPM Circular T (PDF), International Bureau of Weights and Measures, 12 July 2021, archived (PDF) from the original on 9 October 2022, retrieved 16 June 2022
BIPM Annual Report on Time Activities (PDF). Vol. 15. International Bureau of Weights and Measures. 2020. p. 9. ISBN 978-92-822-2280-5. ISSN 1994-9405. Archived (PDF) from the original on 14 August 2021. Retrieved 16 June 2022.
"BIPM Time Dept database". International Bureau of Weights and Measures. Retrieved 20 February 2025.

chainzy.com (Global: low place; English: low place)

"TimeChainZ – Regulatory Reporting For High-Frequency Trading". www.chainzy.com. Retrieved 16 February 2022.

doi.org (Global: 2^nd place; English: 2^nd place)

Thomas P. Heavner; Elizabeth A. Donley; Filippo Levi; Giovanni Costanzo; Thomas E. Parker; Jon H. Shirley; Neil Ashby; Stephan Barlow; Steven R. Jefferts (May 2014). "First Accuracy Evaluation of NIST-F2" (PDF). Metrologia. 51 (3): 174–182. doi:10.1088/0026-1394/51/3/174.
Ramsey, Norman F. (June 2006). "History of early atomic clocks". Metrologia. 42 (3): S1 – S3. doi:10.1088/0026-1394/42/3/s01. ISSN 0026-1394. S2CID 122631200.
Achard, F. (2005). "James Clerk Maxwell, A treatise on electricity and magnetism, first edition (1873)". Landmark Writings in Western Mathematics 1640–1940. Elsevier. pp. 564–587. doi:10.1016/b978-044450871-3/50125-x. ISBN 978-0-444-50871-3.
Rabi, I. I. (15 April 1937). "Space Quantization in a Gyrating Magnetic Field". Physical Review. 51 (8): 652–654. Bibcode:1937PhRv...51..652R. doi:10.1103/physrev.51.652. ISSN 0031-899X.
Rabi, I. I.; Zacharias, J. R.; Millman, S.; Kusch, P. (15 February 1938). "A New Method of Measuring Nuclear Magnetic Moment". Physical Review. 53 (4): 318. Bibcode:1938PhRv...53..318R. doi:10.1103/physrev.53.318. ISSN 0031-899X.
Essen, L.; Parry, J. V. L. (1955). "An Atomic Standard of Frequency and Time Interval: A Cæsium Resonator". Nature. 176 (4476): 280–282. Bibcode:1955Natur.176..280E. doi:10.1038/176280a0. S2CID 4191481.
Essen, L.; Parry, J. V. L. (1955). "An Atomic Standard of Frequency and Time Interval: A Cæsium Resonator". Nature. 176 (4476): 280. Bibcode:1955Natur.176..280E. doi:10.1038/176280a0. S2CID 4191481. p.280.
Ramsey, N. F. (September 1983). "History of Atomic Clocks". Journal of Research of the National Bureau of Standards. 88 (5): 301–320. doi:10.6028/jres.088.015. ISSN 0160-1741. PMC 6768155. PMID 34566107.
"Paper 1.15: "Experiments with Separated Oscillatory Fields and Hydrogen Masers," (Nobel Lecture), N. F. Ramsey, Les Prix Nobel (1989, The Nobel Foundation) and Rev. Mod. Phys. 62, 541–552 (1990)", Spectroscopy With Coherent Radiation, World Scientific Series in 20th Century Physics, vol. 21, WORLD SCIENTIFIC, pp. 115–127, June 1998, doi:10.1142/9789812795717_0015, ISBN 978-981-02-3250-4
Hellwig, Helmut; Evenson, Kenneth M.; Wineland, David J. (December 1978). "Time, frequency and physical measurement". Physics Today. 31 (12): 23–30. Bibcode:1978PhT....31l..23H. doi:10.1063/1.2994867. ISSN 0031-9228.
Lodewyck, Jérôme (16 September 2019). "On a definition of the SI second with a set of optical clock transitions". Metrologia. 56 (5) 055009. arXiv:1911.05551. Bibcode:2019Metro..56e5009L. doi:10.1088/1681-7575/ab3a82. ISSN 0026-1394. S2CID 202129810.
Ye, J.; Schnatz, H.; Hollberg, L. W. (2003). "Optical frequency combs: From frequency metrology to optical phase control" (PDF). IEEE Journal of Selected Topics in Quantum Electronics. 9 (4): 1041–1058. Bibcode:2003IJSTQ...9.1041Y. doi:10.1109/JSTQE.2003.819109. Archived (PDF) from the original on 6 March 2016. Retrieved 25 February 2016.
Nicholson, T. L.; Campbell, S. L.; Hutson, R. B.; Marti, G. E.; Bloom, B. J.; McNally, R. L.; Zhang, W.; Barrett, M. D.; Safronova, M. S.; Strouse, G. F.; Tew, W. L. (21 April 2015). "Systematic evaluation of an atomic clock at 2×10⁻¹⁸ total uncertainty". Nature Communications. 6 (1) 6896. arXiv:1412.8261. Bibcode:2015NatCo...6.6896N. doi:10.1038/ncomms7896. ISSN 2041-1723. PMC 4411304. PMID 25898253.
Brewer, S. M.; Chen, J.-S.; Hankin, A. M.; Clements, E. R.; Chou, C. W.; Wineland, D. J.; Hume, D. B.; Leibrandt, D. R. (15 July 2019). "Al+27 Quantum-Logic Clock with a Systematic Uncertainty below 10⁻¹⁸". Physical Review Letters. 123 (3) 033201. arXiv:1902.07694. doi:10.1103/physrevlett.123.033201. ISSN 0031-9007. PMID 31386450. S2CID 119075546.
Bothwell, Tobias; Kennedy, Colin J.; Aeppli, Alexander; Kedar, Dhruv; Robinson, John M.; Oelker, Eric; Staron, Alexander; Ye, Jun (16 February 2022). "Resolving the gravitational redshift across a millimetre-scale atomic sample". Nature. 602 (7897): 420–424. arXiv:2109.12238. Bibcode:2022Natur.602..420B. doi:10.1038/s41586-021-04349-7. ISSN 0028-0836. PMID 35173346. S2CID 246902611.
Dimarcq, Noel; Gertsvolf, Marina; Mileti, Gaetano; Bize, Sebastien; Oates, Christopher; Peik, Ekkehard; Calonico, Davide; Ido, Tetsuya; Tavella, Patrizia; Meynadier, Frédéric (2024). "Roadmap towards the redefinition of the second". Metrologia. 61 (1): 012001. arXiv:2307.14141. Bibcode:2024Metro..61a2001D. doi:10.1088/1681-7575/ad17d2.
Poli, N (2014). "Optical atomic clocks". La Rivista del Nuovo Cimento. 36 (12): 555. arXiv:1401.2378. Bibcode:2013NCimR..36..555P. doi:10.1393/ncr/i2013-10095-x. S2CID 118430700.
Santarelli, G.; Audoin, C.; Makdissi, A.; Laurent, P.; Dick, G.J.; Clairon, A. (1998). "Frequency stability degradation of an oscillator slaved to a periodically interrogated atomic resonator". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 45 (4): 887–894. Bibcode:1998ITUFF..45..887S. doi:10.1109/58.710548. PMID 18244242. S2CID 12303876.
Ludlow, A. D.; Boyd, M. M.; Ye, Jun; Peik, E.; Schmidt, P. O. (26 June 2015). "Optical atomic clocks". Reviews of Modern Physics. 87 (2): 637–701. arXiv:1407.3493. Bibcode:2015RvMP...87..637L. doi:10.1103/RevModPhys.87.637. S2CID 119116973.
Quessada, A.; Kovacich, R. P.; Courtillot, I.; Clairon, A.; Santarelli, G.; Lemonde, P. (2 April 2003). "The Dick effect for an optical frequency standard". Journal of Optics B: Quantum and Semiclassical Optics. 5 (2): S150 – S154. Bibcode:2003JOptB...5S.150Q. doi:10.1088/1464-4266/5/2/373.
Westergaard, P. G.; Lodewyck, J.; Lemonde, P. (March 2010). "Minimizing the Dick effect in an optical lattice clock". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 57 (3): 623–628. arXiv:0909.0909. Bibcode:2010ITUFF..57..623W. doi:10.1109/TUFFC.2010.1457. PMID 20211780. S2CID 10581032.
Gibney, Elizabeth (2 June 2015). "Hyper-precise atomic clocks face off to redefine time – Next-generation timekeepers can only be tested against each other". Nature. 522 (7554): 16–17. Bibcode:2015Natur.522...16G. doi:10.1038/522016a. PMID 26040875.
Pottie, Paul-Eric; Grosche, Gesine (19 August 2016). "A clock network for geodesy and fundamental science". Nature Communications. 7 12443. arXiv:1511.07735. Bibcode:2016NatCo...712443L. doi:10.1038/ncomms12443. PMC 4980484. PMID 27503795.
Beloy, Kyle; Bodine, Martha I.; Bothwell, Tobias; Brewer, Samuel M.; Bromley, Sarah L.; Chen, Jwo-Sy; Deschênes, Jean-Daniel; Diddams, Scott A.; Fasano, Robert J.; Fortier, Tara M.; Hassan, Youssef S. (25 March 2021). "Frequency ratio measurements at 18-digit accuracy using an optical clock network". Nature. 591 (7851): 564–569. Bibcode:2021Natur.591..564B. doi:10.1038/s41586-021-03253-4. ISSN 1476-4687. PMID 33762766. S2CID 232355391.
Peik, E.; Tamm, Chr. (15 January 2003). "Nuclear laser spectroscopy of the 3.5 eV transition in ²²⁹Th" (PDF). Europhysics Letters. 61 (2): 181–186. Bibcode:2003EL.....61..181P. doi:10.1209/epl/i2003-00210-x. S2CID 250818523. Archived from the original (PDF) on 16 December 2013. Retrieved 11 September 2019.
Campbell, C.; Radnaev, A.G.; Kuzmich, A.; Dzuba, V.A.; Flambaum, V.V.; Derevianko, A. (2012). "A single ion nuclear clock for metrology at the 19th decimal place". Phys. Rev. Lett. 108 (12) 120802. arXiv:1110.2490. Bibcode:2012PhRvL.108l0802C. doi:10.1103/PhysRevLett.108.120802. PMID 22540568. S2CID 40863227.
von der Wense, Lars; Seiferle, Benedict; Laatiaoui, Mustapha; Neumayr, Jürgen B.; Maier, Hans-Jörg; Wirth, Hans-Friedrich; Mokry, Christoph; Runke, Jörg; Eberhardt, Klaus; Düllmann, Christoph E.; Trautmann, Norbert G.; Thirolf, Peter G. (5 May 2016). "Direct detection of the ²²⁹Th nuclear clock transition". Nature. 533 (7601): 47–51. arXiv:1710.11398. Bibcode:2016Natur.533...47V. doi:10.1038/nature17669. PMID 27147026. S2CID 205248786.
Thielking, J.; Okhapkin, M.V.; Glowacki, P.; Meier, D.M.; von der Wense, L.; Seiferle, B.; Düllmann, C.E.; Thirolf, P.G.; Peik, E. (2018). "Laser spectroscopic characterization of the nuclear-clock isomer ^229mTh". Nature. 556 (7701): 321–325. arXiv:1709.05325. Bibcode:2018Natur.556..321T. doi:10.1038/s41586-018-0011-8. PMID 29670266. S2CID 4990345.
Masuda, T.; Yoshimi, A.; Fujieda, A.; Fujimoto, H.; Haba, H.; Hara, H.; Hiraki, T.; Kaino, H.; Kasamatsu, Y.; Kitao, S.; Konashi, K.; Miyamoto, Y.; Okai, K.; Okubo, S.; Sasao, N.; Seto, M.; Schumm, T.; Shigekawa, Y.; Suzuki, K.; Stellmer, S.; Tamasaku, K.; Uetake, S.; Watanabe, M.; Watanabe, T.; Yasuda, Y.; Yamaguchi, A.; Yoda, Y.; Yokokita, T.; Yoshimura, M.; Yoshimura, K. (12 September 2019). "X-ray pumping of the ²²⁹Th nuclear clock isomer". Nature. 573 (7773): 238–242. arXiv:1902.04823. Bibcode:2019Natur.573..238M. doi:10.1038/s41586-019-1542-3. PMID 31511686. S2CID 119083861.
Seiferle, B.; von der Wense, L.; Bilous, P.V.; Amersdorffer, I.; Lemell, C.; Libisch, F.; Stellmer, S.; Schumm, T.; Düllmann, C.E.; Pálffy, A.; Thirolf, P.G. (12 September 2019). "Energy of the ²²⁹Th nuclear clock transition". Nature. 573 (7773): 243–246. arXiv:1905.06308. Bibcode:2019Natur.573..243S. doi:10.1038/s41586-019-1533-4. PMID 31511684. S2CID 155090121.
Thirolf, Peter (29 April 2024). "Shedding Light on the Thorium-229 Nuclear Clock Isomer". Physics. Vol. 17. doi:10.1103/Physics.17.71.
Tiedau, J.; Okhapkin, M. V.; Zhang, K.; Thielking, J.; Zitzer, G.; Peik, E.; et al. (29 April 2024). "Laser Excitation of the Th-229 Nucleus" (PDF). Physical Review Letters. 132 (18) 182501. Bibcode:2024PhRvL.132r2501T. doi:10.1103/PhysRevLett.132.182501. PMID 38759160. The nuclear resonance for the Th⁴⁺ ions in Th:CaF₂ is measured at the wavelength 148.3821(5) nm, frequency 2020.409(7) THz, and the fluorescence lifetime in the crystal is 630(15) s, corresponding to an isomer half-life of 1740(50) s for a nucleus isolated in vacuum.
Elwell, R.; Schneider, Christian; Jeet, Justin; Terhune, J. E. S.; Morgan, H. W. T.; Alexandrova, A. N.; Tran Tan, Hoang Bao; Derevianko, Andrei; Hudson, Eric R. (2 July 2024). "Laser excitation of the ²²⁹Th nuclear isomeric transition in a solid-state host". Physical Review Letters. 133 (1) 013201. arXiv:2404.12311. doi:10.1103/PhysRevLett.133.013201. PMID 39042795. a narrow, laser-linewidth-limited spectral feature at 148.38219(4)_stat(20)_sys nm (2020407.3(5)_stat(30)_sys GHz) that decays with a lifetime of 568(13)_stat(20)_sys s. This feature is assigned to the excitation of the ²²⁹Th nuclear isomeric state, whose energy is found to be 8.355733(2)_stat(10)</sys> eV in ²²⁹Th:LiSrAlF₆.
Zhang, Chuankun; Ooi, Tian; Higgins, Jacob S.; Doyle, Jack F.; von der Wense, Lars; Beeks, Kjeld; Leitner, Adrian; Kazakov, Georgy; Li, Peng; Thirolf, Peter G.; Schumm, Thorsten; Ye, Jun (4 September 2024). "Frequency ratio of the ^229mTh nuclear isomeric transition and the ⁸⁷Sr atomic clock". Nature. 633 (8028): 63–70. arXiv:2406.18719. Bibcode:2024Natur.633...63Z. doi:10.1038/s41586-024-07839-6. PMID 39232152. The transition frequency between the $I = 5/2$ ground state and the $I = 3/2$ excited state is determined as: $𝜈Th = .mw-parser-output .sfrac{white-space:nowrap}.mw-parser-output .sfrac.tion,.mw-parser-output .sfrac .tion{display:inline-block;vertical-align:-0.5em;font-size:85%;text-align:center}.mw-parser-output .sfrac .num{display:block;line-height:1em;margin:0.0em 0.1em;border-bottom:1px solid}.mw-parser-output .sfrac .den{display:block;line-height:1em;margin:0.1em 0.1em}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}⁠1/6⁠ (𝜈a + 2𝜈b + 2𝜈c + 𝜈d) = 2020407384335(2) kHz$ .
Seiferle, Benedict; von der Wense, Lars; Thirolf, Peter G. (2017). "Lifetime measurement of the ²²⁹Th nuclear isomer". Physical Review Letters. 118 (4) 042501. arXiv:1801.05205. Bibcode:2017PhRvL.118d2501S. doi:10.1103/PhysRevLett.118.042501. PMID 28186791. S2CID 37518294. A half-life of 7±1 μs has been measured
National Physical Laboratory (2011). "When should we change the definition of the second?". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 369 (1953): 4109–4130. Bibcode:2011RSPTA.369.4109G. doi:10.1098/rsta.2011.0237. PMID 21930568. S2CID 6896025.
Gill, Patrick (28 October 2011). "When should we change the definition of the second?". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 369 (1953): 4109–4130. Bibcode:2011RSPTA.369.4109G. doi:10.1098/rsta.2011.0237. PMID 21930568. S2CID 6896025.
Essen, L; Donaldson, R W; Hope, E G; Bangham, M J (July 1973). "Hydrogen Maser Work at the National Physical Laboratory". Metrologia. 9 (3): 128–137. Bibcode:1973Metro...9..128E. doi:10.1088/0026-1394/9/3/004. S2CID 250828528.
Dupays, Arnaud; Beswick, Alberto; Lepetit, Bruno; Rizzo, Carlo (August 2003). "Proton Zemach radius from measurements of the hyperfine splitting of hydrogen and muonic hydrogen" (PDF). Physical Review A. 68 (5) 052503. arXiv:quant-ph/0308136. Bibcode:2003PhRvA..68e2503D. doi:10.1103/PhysRevA.68.052503. S2CID 3957861. Archived (PDF) from the original on 14 January 2019. Retrieved 26 September 2016.
Brewer, S.; Chen, J.-S.; Hankin, A.; Clements, E. (15 July 2019). "²⁷Al⁺ Quantum-Logic Clock with a Systematic Uncertainty below 10⁻¹⁸". Physical Review Letters. 123 (3) 033201. arXiv:1902.07694. Bibcode:2019PhRvL.123c3201B. doi:10.1103/PhysRevLett.123.033201. PMID 31386450. S2CID 119075546.
Huntemann, N.; Sanner, C.; Lipphardt, B.; Tamm, Chr. (8 February 2016). "Single-Ion Atomic Clock with 3×10⁻¹⁸ Systematic Uncertainty". Physical Review Letters. 116 (6) 063001. arXiv:1602.03908. Bibcode:2016PhRvL.116f3001H. doi:10.1103/PhysRevLett.116.063001. PMID 26918984. S2CID 19870627.
Leute, J.; Huntemann, N.; Lipphardt, B.; Tamm, Christian (3 February 2016). "Frequency Comparison of ¹⁷¹Yb⁺ Ion Optical Clocks at PTB and NPL via GPS PPP". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 63 (7): 981–985. arXiv:1507.04754. doi:10.1109/TUFFC.2016.2524988. PMID 26863657. S2CID 20466105.
Ren, Wei; Li, Tang; Qu, Qiuzhi; Wang, Bin; Li, Lin; Lü, Desheng; Chen, Weibiao; Liu, Liang (18 December 2020). "Development of a space cold atom clock". National Science Review. 7 (12): 1828–1836. doi:10.1093/nsr/nwaa215. ISSN 2095-5138. PMC 8288775. PMID 34691520.
Bothwell, Tobias; Kennedy, Colin J.; Aeppli, Alexander; Kedar, Dhruv; Robinson, John M.; Oelker, Eric; Staron, Alexander; Ye, Jun (2022). "Resolving the gravitational redshift across a millimetre-scale atomic sample". Nature. 602 (7897): 420–424. arXiv:2109.12238. Bibcode:2022Natur.602..420B. doi:10.1038/s41586-021-04349-7. PMID 35173346. S2CID 237940816.
Koller, S. B.; Grotti, J.; Vogt, St.; Al-Masoudi, A.; Dörscher, S.; Häfner, S.; Sterr, U.; Lisdat, Ch. (13 February 2017). "Transportable Optical Lattice Clock with 7×10⁻¹⁷ Uncertainty". Physical Review Letters. 118 (7) 073601. arXiv:1609.06183. doi:10.1103/PhysRevLett.118.073601. ISSN 0031-9007. PMID 28256845. S2CID 40822816.

esa.int (Global: 1,482^nd place; English: 1,468^th place)

"Galileo begins serving the globe". European Space Agency. Archived from the original on 13 September 2019. Retrieved 15 December 2016.
"Galileo's clocks". European Space Agency. Archived from the original on 29 August 2019. Retrieved 16 January 2017.

eso.org (Global: 3,034^th place; English: 2,650^th place)

"President Piñera Receives ESO's First Atomic Clock". ESO Announcement. 15 November 2013. Archived from the original on 1 April 2014. Retrieved 20 November 2013.

ethw.org (Global: low place; English: 7,456^th place)

"Milestones:First Atomic Clock, 1948". ETHW. 14 June 2022. Retrieved 20 June 2022.
Sullivan, D. B. (2001). Time and frequency measurement at NIST: The first 100 years (PDF). IEEE International Frequency Control Symposium. NIST. pp. 4–17. Archived (PDF) from the original on 29 December 2019. Retrieved 1 May 2018.

eurekalert.org (Global: 3,538^th place; English: 3,083^rd place)

University of Wisconsin-Madison. "Ultraprecise atomic clock poised for new physics discoveries".
"The atomic clock with the world's best long-term accuracy is revealed after evaluation". EurekAlert!. Retrieved 20 February 2022.

europa.eu (Global: 68^th place; English: 117^th place)

ec.europa.eu

"Galileo's contribution to the MEOSAR system". European Commission. Archived from the original on 9 July 2016. Retrieved 30 December 2015.

gsa.europa.eu

"Galileo Goes Live". European GNSS Agency. 15 December 2016. Archived from the original on 15 January 2021. Retrieved 1 February 2017.

galleon.eu.com (Global: low place; English: low place)

atomic-clock.galleon.eu.com

"GPS time accurate to 100 nanoseconds". Galleon. Archived from the original on 14 May 2012. Retrieved 12 October 2012.

ghostarchive.org (Global: 32^nd place; English: 21^st place)

Explanatory Supplement of BIPM Circular T (PDF), International Bureau of Weights and Measures, 12 July 2021, archived (PDF) from the original on 9 October 2022, retrieved 16 June 2022

gps.gov (Global: low place; English: low place)

"Global Positioning System". Gps.gov. Archived from the original on 30 July 2010. Retrieved 26 June 2010.

gsc-europa.eu (Global: low place; English: low place)

"European GNSS (Galileo) Open Service Signal-In-Space Operational Status Definition, Issue 1.0, September 2015" (PDF). Archived from the original (PDF) on 9 January 2017. Retrieved 3 October 2015.
"Galileo Initial Services – Open Service – Quarterly Performance Report Oct–Nov–Dec 2017" (PDF). European GNSS Service Centre. 28 March 2018. Archived (PDF) from the original on 26 August 2019. Retrieved 28 March 2017.
"Galileo Open Service and Search and Rescue – Quarterly Performance Reports, containing measured performance statistics". Archived from the original on 26 August 2019. Retrieved 3 March 2019.

gsi.de (Global: low place; English: low place)

indico.gsi.de

Peik, Ekkehard (25–27 September 2012). Concepts and Prospects for a Thorium-229 Nuclear Clock (PDF). EMMI Workshop: The ^229mTh Nuclear Isomer Clock. Darmstadt. Archived (PDF) from the original on 10 October 2021. Retrieved 2 December 2019.

harvard.edu (Global: 18^th place; English: 17^th place)

ui.adsabs.harvard.edu

Rabi, I. I. (15 April 1937). "Space Quantization in a Gyrating Magnetic Field". Physical Review. 51 (8): 652–654. Bibcode:1937PhRv...51..652R. doi:10.1103/physrev.51.652. ISSN 0031-899X.
Rabi, I. I.; Zacharias, J. R.; Millman, S.; Kusch, P. (15 February 1938). "A New Method of Measuring Nuclear Magnetic Moment". Physical Review. 53 (4): 318. Bibcode:1938PhRv...53..318R. doi:10.1103/physrev.53.318. ISSN 0031-899X.
Essen, L.; Parry, J. V. L. (1955). "An Atomic Standard of Frequency and Time Interval: A Cæsium Resonator". Nature. 176 (4476): 280–282. Bibcode:1955Natur.176..280E. doi:10.1038/176280a0. S2CID 4191481.
Essen, L.; Parry, J. V. L. (1955). "An Atomic Standard of Frequency and Time Interval: A Cæsium Resonator". Nature. 176 (4476): 280. Bibcode:1955Natur.176..280E. doi:10.1038/176280a0. S2CID 4191481. p.280.
Hellwig, Helmut; Evenson, Kenneth M.; Wineland, David J. (December 1978). "Time, frequency and physical measurement". Physics Today. 31 (12): 23–30. Bibcode:1978PhT....31l..23H. doi:10.1063/1.2994867. ISSN 0031-9228.
Lodewyck, Jérôme (16 September 2019). "On a definition of the SI second with a set of optical clock transitions". Metrologia. 56 (5) 055009. arXiv:1911.05551. Bibcode:2019Metro..56e5009L. doi:10.1088/1681-7575/ab3a82. ISSN 0026-1394. S2CID 202129810.
Ye, J.; Schnatz, H.; Hollberg, L. W. (2003). "Optical frequency combs: From frequency metrology to optical phase control" (PDF). IEEE Journal of Selected Topics in Quantum Electronics. 9 (4): 1041–1058. Bibcode:2003IJSTQ...9.1041Y. doi:10.1109/JSTQE.2003.819109. Archived (PDF) from the original on 6 March 2016. Retrieved 25 February 2016.
Nicholson, T. L.; Campbell, S. L.; Hutson, R. B.; Marti, G. E.; Bloom, B. J.; McNally, R. L.; Zhang, W.; Barrett, M. D.; Safronova, M. S.; Strouse, G. F.; Tew, W. L. (21 April 2015). "Systematic evaluation of an atomic clock at 2×10⁻¹⁸ total uncertainty". Nature Communications. 6 (1) 6896. arXiv:1412.8261. Bibcode:2015NatCo...6.6896N. doi:10.1038/ncomms7896. ISSN 2041-1723. PMC 4411304. PMID 25898253.
Bothwell, Tobias; Kennedy, Colin J.; Aeppli, Alexander; Kedar, Dhruv; Robinson, John M.; Oelker, Eric; Staron, Alexander; Ye, Jun (16 February 2022). "Resolving the gravitational redshift across a millimetre-scale atomic sample". Nature. 602 (7897): 420–424. arXiv:2109.12238. Bibcode:2022Natur.602..420B. doi:10.1038/s41586-021-04349-7. ISSN 0028-0836. PMID 35173346. S2CID 246902611.
Dimarcq, Noel; Gertsvolf, Marina; Mileti, Gaetano; Bize, Sebastien; Oates, Christopher; Peik, Ekkehard; Calonico, Davide; Ido, Tetsuya; Tavella, Patrizia; Meynadier, Frédéric (2024). "Roadmap towards the redefinition of the second". Metrologia. 61 (1): 012001. arXiv:2307.14141. Bibcode:2024Metro..61a2001D. doi:10.1088/1681-7575/ad17d2.
Poli, N (2014). "Optical atomic clocks". La Rivista del Nuovo Cimento. 36 (12): 555. arXiv:1401.2378. Bibcode:2013NCimR..36..555P. doi:10.1393/ncr/i2013-10095-x. S2CID 118430700.
Santarelli, G.; Audoin, C.; Makdissi, A.; Laurent, P.; Dick, G.J.; Clairon, A. (1998). "Frequency stability degradation of an oscillator slaved to a periodically interrogated atomic resonator". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 45 (4): 887–894. Bibcode:1998ITUFF..45..887S. doi:10.1109/58.710548. PMID 18244242. S2CID 12303876.
Ludlow, A. D.; Boyd, M. M.; Ye, Jun; Peik, E.; Schmidt, P. O. (26 June 2015). "Optical atomic clocks". Reviews of Modern Physics. 87 (2): 637–701. arXiv:1407.3493. Bibcode:2015RvMP...87..637L. doi:10.1103/RevModPhys.87.637. S2CID 119116973.
Quessada, A.; Kovacich, R. P.; Courtillot, I.; Clairon, A.; Santarelli, G.; Lemonde, P. (2 April 2003). "The Dick effect for an optical frequency standard". Journal of Optics B: Quantum and Semiclassical Optics. 5 (2): S150 – S154. Bibcode:2003JOptB...5S.150Q. doi:10.1088/1464-4266/5/2/373.
Westergaard, P. G.; Lodewyck, J.; Lemonde, P. (March 2010). "Minimizing the Dick effect in an optical lattice clock". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 57 (3): 623–628. arXiv:0909.0909. Bibcode:2010ITUFF..57..623W. doi:10.1109/TUFFC.2010.1457. PMID 20211780. S2CID 10581032.
Gibney, Elizabeth (2 June 2015). "Hyper-precise atomic clocks face off to redefine time – Next-generation timekeepers can only be tested against each other". Nature. 522 (7554): 16–17. Bibcode:2015Natur.522...16G. doi:10.1038/522016a. PMID 26040875.
Pottie, Paul-Eric; Grosche, Gesine (19 August 2016). "A clock network for geodesy and fundamental science". Nature Communications. 7 12443. arXiv:1511.07735. Bibcode:2016NatCo...712443L. doi:10.1038/ncomms12443. PMC 4980484. PMID 27503795.
Beloy, Kyle; Bodine, Martha I.; Bothwell, Tobias; Brewer, Samuel M.; Bromley, Sarah L.; Chen, Jwo-Sy; Deschênes, Jean-Daniel; Diddams, Scott A.; Fasano, Robert J.; Fortier, Tara M.; Hassan, Youssef S. (25 March 2021). "Frequency ratio measurements at 18-digit accuracy using an optical clock network". Nature. 591 (7851): 564–569. Bibcode:2021Natur.591..564B. doi:10.1038/s41586-021-03253-4. ISSN 1476-4687. PMID 33762766. S2CID 232355391.
Peik, E.; Tamm, Chr. (15 January 2003). "Nuclear laser spectroscopy of the 3.5 eV transition in ²²⁹Th" (PDF). Europhysics Letters. 61 (2): 181–186. Bibcode:2003EL.....61..181P. doi:10.1209/epl/i2003-00210-x. S2CID 250818523. Archived from the original (PDF) on 16 December 2013. Retrieved 11 September 2019.
Campbell, C.; Radnaev, A.G.; Kuzmich, A.; Dzuba, V.A.; Flambaum, V.V.; Derevianko, A. (2012). "A single ion nuclear clock for metrology at the 19th decimal place". Phys. Rev. Lett. 108 (12) 120802. arXiv:1110.2490. Bibcode:2012PhRvL.108l0802C. doi:10.1103/PhysRevLett.108.120802. PMID 22540568. S2CID 40863227.
von der Wense, Lars; Seiferle, Benedict; Laatiaoui, Mustapha; Neumayr, Jürgen B.; Maier, Hans-Jörg; Wirth, Hans-Friedrich; Mokry, Christoph; Runke, Jörg; Eberhardt, Klaus; Düllmann, Christoph E.; Trautmann, Norbert G.; Thirolf, Peter G. (5 May 2016). "Direct detection of the ²²⁹Th nuclear clock transition". Nature. 533 (7601): 47–51. arXiv:1710.11398. Bibcode:2016Natur.533...47V. doi:10.1038/nature17669. PMID 27147026. S2CID 205248786.
Thielking, J.; Okhapkin, M.V.; Glowacki, P.; Meier, D.M.; von der Wense, L.; Seiferle, B.; Düllmann, C.E.; Thirolf, P.G.; Peik, E. (2018). "Laser spectroscopic characterization of the nuclear-clock isomer ^229mTh". Nature. 556 (7701): 321–325. arXiv:1709.05325. Bibcode:2018Natur.556..321T. doi:10.1038/s41586-018-0011-8. PMID 29670266. S2CID 4990345.
Masuda, T.; Yoshimi, A.; Fujieda, A.; Fujimoto, H.; Haba, H.; Hara, H.; Hiraki, T.; Kaino, H.; Kasamatsu, Y.; Kitao, S.; Konashi, K.; Miyamoto, Y.; Okai, K.; Okubo, S.; Sasao, N.; Seto, M.; Schumm, T.; Shigekawa, Y.; Suzuki, K.; Stellmer, S.; Tamasaku, K.; Uetake, S.; Watanabe, M.; Watanabe, T.; Yasuda, Y.; Yamaguchi, A.; Yoda, Y.; Yokokita, T.; Yoshimura, M.; Yoshimura, K. (12 September 2019). "X-ray pumping of the ²²⁹Th nuclear clock isomer". Nature. 573 (7773): 238–242. arXiv:1902.04823. Bibcode:2019Natur.573..238M. doi:10.1038/s41586-019-1542-3. PMID 31511686. S2CID 119083861.
Seiferle, B.; von der Wense, L.; Bilous, P.V.; Amersdorffer, I.; Lemell, C.; Libisch, F.; Stellmer, S.; Schumm, T.; Düllmann, C.E.; Pálffy, A.; Thirolf, P.G. (12 September 2019). "Energy of the ²²⁹Th nuclear clock transition". Nature. 573 (7773): 243–246. arXiv:1905.06308. Bibcode:2019Natur.573..243S. doi:10.1038/s41586-019-1533-4. PMID 31511684. S2CID 155090121.
Tiedau, J.; Okhapkin, M. V.; Zhang, K.; Thielking, J.; Zitzer, G.; Peik, E.; et al. (29 April 2024). "Laser Excitation of the Th-229 Nucleus" (PDF). Physical Review Letters. 132 (18) 182501. Bibcode:2024PhRvL.132r2501T. doi:10.1103/PhysRevLett.132.182501. PMID 38759160. The nuclear resonance for the Th⁴⁺ ions in Th:CaF₂ is measured at the wavelength 148.3821(5) nm, frequency 2020.409(7) THz, and the fluorescence lifetime in the crystal is 630(15) s, corresponding to an isomer half-life of 1740(50) s for a nucleus isolated in vacuum.
Zhang, Chuankun; Ooi, Tian; Higgins, Jacob S.; Doyle, Jack F.; von der Wense, Lars; Beeks, Kjeld; Leitner, Adrian; Kazakov, Georgy; Li, Peng; Thirolf, Peter G.; Schumm, Thorsten; Ye, Jun (4 September 2024). "Frequency ratio of the ^229mTh nuclear isomeric transition and the ⁸⁷Sr atomic clock". Nature. 633 (8028): 63–70. arXiv:2406.18719. Bibcode:2024Natur.633...63Z. doi:10.1038/s41586-024-07839-6. PMID 39232152. The transition frequency between the $I = 5/2$ ground state and the $I = 3/2$ excited state is determined as: $𝜈Th = .mw-parser-output .sfrac{white-space:nowrap}.mw-parser-output .sfrac.tion,.mw-parser-output .sfrac .tion{display:inline-block;vertical-align:-0.5em;font-size:85%;text-align:center}.mw-parser-output .sfrac .num{display:block;line-height:1em;margin:0.0em 0.1em;border-bottom:1px solid}.mw-parser-output .sfrac .den{display:block;line-height:1em;margin:0.1em 0.1em}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}⁠1/6⁠ (𝜈a + 2𝜈b + 2𝜈c + 𝜈d) = 2020407384335(2) kHz$ .
Seiferle, Benedict; von der Wense, Lars; Thirolf, Peter G. (2017). "Lifetime measurement of the ²²⁹Th nuclear isomer". Physical Review Letters. 118 (4) 042501. arXiv:1801.05205. Bibcode:2017PhRvL.118d2501S. doi:10.1103/PhysRevLett.118.042501. PMID 28186791. S2CID 37518294. A half-life of 7±1 μs has been measured
National Physical Laboratory (2011). "When should we change the definition of the second?". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 369 (1953): 4109–4130. Bibcode:2011RSPTA.369.4109G. doi:10.1098/rsta.2011.0237. PMID 21930568. S2CID 6896025.
Gill, Patrick (28 October 2011). "When should we change the definition of the second?". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 369 (1953): 4109–4130. Bibcode:2011RSPTA.369.4109G. doi:10.1098/rsta.2011.0237. PMID 21930568. S2CID 6896025.
Essen, L; Donaldson, R W; Hope, E G; Bangham, M J (July 1973). "Hydrogen Maser Work at the National Physical Laboratory". Metrologia. 9 (3): 128–137. Bibcode:1973Metro...9..128E. doi:10.1088/0026-1394/9/3/004. S2CID 250828528.
Dupays, Arnaud; Beswick, Alberto; Lepetit, Bruno; Rizzo, Carlo (August 2003). "Proton Zemach radius from measurements of the hyperfine splitting of hydrogen and muonic hydrogen" (PDF). Physical Review A. 68 (5) 052503. arXiv:quant-ph/0308136. Bibcode:2003PhRvA..68e2503D. doi:10.1103/PhysRevA.68.052503. S2CID 3957861. Archived (PDF) from the original on 14 January 2019. Retrieved 26 September 2016.
Brewer, S.; Chen, J.-S.; Hankin, A.; Clements, E. (15 July 2019). "²⁷Al⁺ Quantum-Logic Clock with a Systematic Uncertainty below 10⁻¹⁸". Physical Review Letters. 123 (3) 033201. arXiv:1902.07694. Bibcode:2019PhRvL.123c3201B. doi:10.1103/PhysRevLett.123.033201. PMID 31386450. S2CID 119075546.
Huntemann, N.; Sanner, C.; Lipphardt, B.; Tamm, Chr. (8 February 2016). "Single-Ion Atomic Clock with 3×10⁻¹⁸ Systematic Uncertainty". Physical Review Letters. 116 (6) 063001. arXiv:1602.03908. Bibcode:2016PhRvL.116f3001H. doi:10.1103/PhysRevLett.116.063001. PMID 26918984. S2CID 19870627.
Bothwell, Tobias; Kennedy, Colin J.; Aeppli, Alexander; Kedar, Dhruv; Robinson, John M.; Oelker, Eric; Staron, Alexander; Ye, Jun (2022). "Resolving the gravitational redshift across a millimetre-scale atomic sample". Nature. 602 (7897): 420–424. arXiv:2109.12238. Bibcode:2022Natur.602..420B. doi:10.1038/s41586-021-04349-7. PMID 35173346. S2CID 237940816.

hparchive.com (Global: low place; English: low place)

"A Cesium Beam Frequency Reference for Severe Environment" (PDF). Retrieved 24 February 2022.

ieee-uffc.org (Global: low place; English: low place)

Forman, Paul (1998). "Atomichron: The Atomic Clock from Concept to Commercial Product". Archived from the original on 21 October 2007. Retrieved 16 February 2022.

insidegnss.com (Global: low place; English: low place)

"ESA Adds System Time Offset to Galileo Navigation Message". insidegnss.com. Archived from the original on 28 March 2018. Retrieved 5 October 2015.

iop.org (Global: 1,725^th place; English: 1,828^th place)

iopscience.iop.org

Ramsey, Norman F. (June 2006). "History of early atomic clocks". Metrologia. 42 (3): S1 – S3. doi:10.1088/0026-1394/42/3/s01. ISSN 0026-1394. S2CID 122631200.
Lodewyck, Jérôme (16 September 2019). "On a definition of the SI second with a set of optical clock transitions". Metrologia. 56 (5) 055009. arXiv:1911.05551. Bibcode:2019Metro..56e5009L. doi:10.1088/1681-7575/ab3a82. ISSN 0026-1394. S2CID 202129810.
Dimarcq, Noel; Gertsvolf, Marina; Mileti, Gaetano; Bize, Sebastien; Oates, Christopher; Peik, Ekkehard; Calonico, Davide; Ido, Tetsuya; Tavella, Patrizia; Meynadier, Frédéric (2024). "Roadmap towards the redefinition of the second". Metrologia. 61 (1): 012001. arXiv:2307.14141. Bibcode:2024Metro..61a2001D. doi:10.1088/1681-7575/ad17d2.

laserfocusworld.com (Global: low place; English: low place)

"StackPath". www.laserfocusworld.com. September 2001. Retrieved 11 February 2022.

livemint.com (Global: 390^th place; English: 227^th place)

Varma, K. J. M. (27 December 2018). "China's BeiDou navigation satellite, rival to US GPS, starts global services". livemint.com. Archived from the original on 27 December 2018. Retrieved 27 December 2018.

mit.edu (Global: 415^th place; English: 327^th place)

news.mit.edu

"New type of atomic clock keeps time even more precisely". MIT News | Massachusetts Institute of Technology. 16 December 2020. Retrieved 11 February 2022.

nasa.gov (Global: 75^th place; English: 83^rd place)

jpl.nasa.gov

Landau, Elizabeth (27 April 2015). "Deep Space Atomic Clock". NASA. Archived from the original on 10 December 2015. Retrieved 29 April 2015.
"NASA Activates Deep Space Atomic Clock". NASA Jet Propulsion Laboratory (JPL). Retrieved 20 February 2022.

nasa.gov

Northon, Karen (25 June 2019). "NASA Technology Missions Launch on SpaceX Falcon Heavy". NASA. Retrieved 20 February 2022.
Hartono, Naomi (1 October 2021). "Working Overtime: NASA's Deep Space Atomic Clock Completes Mission". NASA. Retrieved 20 February 2022.

grc.nasa.gov

"Temperature and Kinetic Energy – Answers". www.grc.nasa.gov. Retrieved 19 February 2022.

nature.com (Global: 234^th place; English: 397^th place)

Beloy, Kyle; Bodine, Martha I.; Bothwell, Tobias; Brewer, Samuel M.; Bromley, Sarah L.; Chen, Jwo-Sy; Deschênes, Jean-Daniel; Diddams, Scott A.; Fasano, Robert J.; Fortier, Tara M.; Hassan, Youssef S. (25 March 2021). "Frequency ratio measurements at 18-digit accuracy using an optical clock network". Nature. 591 (7851): 564–569. Bibcode:2021Natur.591..564B. doi:10.1038/s41586-021-03253-4. ISSN 1476-4687. PMID 33762766. S2CID 232355391.

navipedia.net (Global: low place; English: low place)

"Time References in GNSS". navipedia.net. Archived from the original on 2 June 2018. Retrieved 2 October 2015.

navy.mil (Global: 237^th place; English: 170^th place)

usno.navy.mil

"USNO Master Clock". Archived from the original on 7 December 2010. Retrieved 23 November 2010.

tycho.usno.navy.mil

Dick, G. J. (1987). Local oscillator induced instabilities in trapped ion frequency standards (PDF). Precise Time and Time Interval (PTTI) Conference. Redondo Beach. Archived from the original (PDF) on 19 October 2016.

newscientist.com (Global: 774^th place; English: 716^th place)

Woodward, Aylin (5 October 2017). "The most precise atomic clock ever made is a cube of quantum gas". New Scientist. Retrieved 11 February 2022.

nih.gov (Global: 4^th place; English: 4^th place)

pubmed.ncbi.nlm.nih.gov

Ramsey, N. F. (September 1983). "History of Atomic Clocks". Journal of Research of the National Bureau of Standards. 88 (5): 301–320. doi:10.6028/jres.088.015. ISSN 0160-1741. PMC 6768155. PMID 34566107.
Nicholson, T. L.; Campbell, S. L.; Hutson, R. B.; Marti, G. E.; Bloom, B. J.; McNally, R. L.; Zhang, W.; Barrett, M. D.; Safronova, M. S.; Strouse, G. F.; Tew, W. L. (21 April 2015). "Systematic evaluation of an atomic clock at 2×10⁻¹⁸ total uncertainty". Nature Communications. 6 (1) 6896. arXiv:1412.8261. Bibcode:2015NatCo...6.6896N. doi:10.1038/ncomms7896. ISSN 2041-1723. PMC 4411304. PMID 25898253.
Brewer, S. M.; Chen, J.-S.; Hankin, A. M.; Clements, E. R.; Chou, C. W.; Wineland, D. J.; Hume, D. B.; Leibrandt, D. R. (15 July 2019). "Al+27 Quantum-Logic Clock with a Systematic Uncertainty below 10⁻¹⁸". Physical Review Letters. 123 (3) 033201. arXiv:1902.07694. doi:10.1103/physrevlett.123.033201. ISSN 0031-9007. PMID 31386450. S2CID 119075546.
Bothwell, Tobias; Kennedy, Colin J.; Aeppli, Alexander; Kedar, Dhruv; Robinson, John M.; Oelker, Eric; Staron, Alexander; Ye, Jun (16 February 2022). "Resolving the gravitational redshift across a millimetre-scale atomic sample". Nature. 602 (7897): 420–424. arXiv:2109.12238. Bibcode:2022Natur.602..420B. doi:10.1038/s41586-021-04349-7. ISSN 0028-0836. PMID 35173346. S2CID 246902611.
Santarelli, G.; Audoin, C.; Makdissi, A.; Laurent, P.; Dick, G.J.; Clairon, A. (1998). "Frequency stability degradation of an oscillator slaved to a periodically interrogated atomic resonator". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 45 (4): 887–894. Bibcode:1998ITUFF..45..887S. doi:10.1109/58.710548. PMID 18244242. S2CID 12303876.
Westergaard, P. G.; Lodewyck, J.; Lemonde, P. (March 2010). "Minimizing the Dick effect in an optical lattice clock". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 57 (3): 623–628. arXiv:0909.0909. Bibcode:2010ITUFF..57..623W. doi:10.1109/TUFFC.2010.1457. PMID 20211780. S2CID 10581032.
Gibney, Elizabeth (2 June 2015). "Hyper-precise atomic clocks face off to redefine time – Next-generation timekeepers can only be tested against each other". Nature. 522 (7554): 16–17. Bibcode:2015Natur.522...16G. doi:10.1038/522016a. PMID 26040875.
Pottie, Paul-Eric; Grosche, Gesine (19 August 2016). "A clock network for geodesy and fundamental science". Nature Communications. 7 12443. arXiv:1511.07735. Bibcode:2016NatCo...712443L. doi:10.1038/ncomms12443. PMC 4980484. PMID 27503795.
Beloy, Kyle; Bodine, Martha I.; Bothwell, Tobias; Brewer, Samuel M.; Bromley, Sarah L.; Chen, Jwo-Sy; Deschênes, Jean-Daniel; Diddams, Scott A.; Fasano, Robert J.; Fortier, Tara M.; Hassan, Youssef S. (25 March 2021). "Frequency ratio measurements at 18-digit accuracy using an optical clock network". Nature. 591 (7851): 564–569. Bibcode:2021Natur.591..564B. doi:10.1038/s41586-021-03253-4. ISSN 1476-4687. PMID 33762766. S2CID 232355391.
Campbell, C.; Radnaev, A.G.; Kuzmich, A.; Dzuba, V.A.; Flambaum, V.V.; Derevianko, A. (2012). "A single ion nuclear clock for metrology at the 19th decimal place". Phys. Rev. Lett. 108 (12) 120802. arXiv:1110.2490. Bibcode:2012PhRvL.108l0802C. doi:10.1103/PhysRevLett.108.120802. PMID 22540568. S2CID 40863227.
von der Wense, Lars; Seiferle, Benedict; Laatiaoui, Mustapha; Neumayr, Jürgen B.; Maier, Hans-Jörg; Wirth, Hans-Friedrich; Mokry, Christoph; Runke, Jörg; Eberhardt, Klaus; Düllmann, Christoph E.; Trautmann, Norbert G.; Thirolf, Peter G. (5 May 2016). "Direct detection of the ²²⁹Th nuclear clock transition". Nature. 533 (7601): 47–51. arXiv:1710.11398. Bibcode:2016Natur.533...47V. doi:10.1038/nature17669. PMID 27147026. S2CID 205248786.
Thielking, J.; Okhapkin, M.V.; Glowacki, P.; Meier, D.M.; von der Wense, L.; Seiferle, B.; Düllmann, C.E.; Thirolf, P.G.; Peik, E. (2018). "Laser spectroscopic characterization of the nuclear-clock isomer ^229mTh". Nature. 556 (7701): 321–325. arXiv:1709.05325. Bibcode:2018Natur.556..321T. doi:10.1038/s41586-018-0011-8. PMID 29670266. S2CID 4990345.
Masuda, T.; Yoshimi, A.; Fujieda, A.; Fujimoto, H.; Haba, H.; Hara, H.; Hiraki, T.; Kaino, H.; Kasamatsu, Y.; Kitao, S.; Konashi, K.; Miyamoto, Y.; Okai, K.; Okubo, S.; Sasao, N.; Seto, M.; Schumm, T.; Shigekawa, Y.; Suzuki, K.; Stellmer, S.; Tamasaku, K.; Uetake, S.; Watanabe, M.; Watanabe, T.; Yasuda, Y.; Yamaguchi, A.; Yoda, Y.; Yokokita, T.; Yoshimura, M.; Yoshimura, K. (12 September 2019). "X-ray pumping of the ²²⁹Th nuclear clock isomer". Nature. 573 (7773): 238–242. arXiv:1902.04823. Bibcode:2019Natur.573..238M. doi:10.1038/s41586-019-1542-3. PMID 31511686. S2CID 119083861.
Seiferle, B.; von der Wense, L.; Bilous, P.V.; Amersdorffer, I.; Lemell, C.; Libisch, F.; Stellmer, S.; Schumm, T.; Düllmann, C.E.; Pálffy, A.; Thirolf, P.G. (12 September 2019). "Energy of the ²²⁹Th nuclear clock transition". Nature. 573 (7773): 243–246. arXiv:1905.06308. Bibcode:2019Natur.573..243S. doi:10.1038/s41586-019-1533-4. PMID 31511684. S2CID 155090121.
Tiedau, J.; Okhapkin, M. V.; Zhang, K.; Thielking, J.; Zitzer, G.; Peik, E.; et al. (29 April 2024). "Laser Excitation of the Th-229 Nucleus" (PDF). Physical Review Letters. 132 (18) 182501. Bibcode:2024PhRvL.132r2501T. doi:10.1103/PhysRevLett.132.182501. PMID 38759160. The nuclear resonance for the Th⁴⁺ ions in Th:CaF₂ is measured at the wavelength 148.3821(5) nm, frequency 2020.409(7) THz, and the fluorescence lifetime in the crystal is 630(15) s, corresponding to an isomer half-life of 1740(50) s for a nucleus isolated in vacuum.
Elwell, R.; Schneider, Christian; Jeet, Justin; Terhune, J. E. S.; Morgan, H. W. T.; Alexandrova, A. N.; Tran Tan, Hoang Bao; Derevianko, Andrei; Hudson, Eric R. (2 July 2024). "Laser excitation of the ²²⁹Th nuclear isomeric transition in a solid-state host". Physical Review Letters. 133 (1) 013201. arXiv:2404.12311. doi:10.1103/PhysRevLett.133.013201. PMID 39042795. a narrow, laser-linewidth-limited spectral feature at 148.38219(4)_stat(20)_sys nm (2020407.3(5)_stat(30)_sys GHz) that decays with a lifetime of 568(13)_stat(20)_sys s. This feature is assigned to the excitation of the ²²⁹Th nuclear isomeric state, whose energy is found to be 8.355733(2)_stat(10)</sys> eV in ²²⁹Th:LiSrAlF₆.
Zhang, Chuankun; Ooi, Tian; Higgins, Jacob S.; Doyle, Jack F.; von der Wense, Lars; Beeks, Kjeld; Leitner, Adrian; Kazakov, Georgy; Li, Peng; Thirolf, Peter G.; Schumm, Thorsten; Ye, Jun (4 September 2024). "Frequency ratio of the ^229mTh nuclear isomeric transition and the ⁸⁷Sr atomic clock". Nature. 633 (8028): 63–70. arXiv:2406.18719. Bibcode:2024Natur.633...63Z. doi:10.1038/s41586-024-07839-6. PMID 39232152. The transition frequency between the $I = 5/2$ ground state and the $I = 3/2$ excited state is determined as: $𝜈Th = .mw-parser-output .sfrac{white-space:nowrap}.mw-parser-output .sfrac.tion,.mw-parser-output .sfrac .tion{display:inline-block;vertical-align:-0.5em;font-size:85%;text-align:center}.mw-parser-output .sfrac .num{display:block;line-height:1em;margin:0.0em 0.1em;border-bottom:1px solid}.mw-parser-output .sfrac .den{display:block;line-height:1em;margin:0.1em 0.1em}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}⁠1/6⁠ (𝜈a + 2𝜈b + 2𝜈c + 𝜈d) = 2020407384335(2) kHz$ .
Seiferle, Benedict; von der Wense, Lars; Thirolf, Peter G. (2017). "Lifetime measurement of the ²²⁹Th nuclear isomer". Physical Review Letters. 118 (4) 042501. arXiv:1801.05205. Bibcode:2017PhRvL.118d2501S. doi:10.1103/PhysRevLett.118.042501. PMID 28186791. S2CID 37518294. A half-life of 7±1 μs has been measured
National Physical Laboratory (2011). "When should we change the definition of the second?". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 369 (1953): 4109–4130. Bibcode:2011RSPTA.369.4109G. doi:10.1098/rsta.2011.0237. PMID 21930568. S2CID 6896025.
Gill, Patrick (28 October 2011). "When should we change the definition of the second?". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 369 (1953): 4109–4130. Bibcode:2011RSPTA.369.4109G. doi:10.1098/rsta.2011.0237. PMID 21930568. S2CID 6896025.
Brewer, S.; Chen, J.-S.; Hankin, A.; Clements, E. (15 July 2019). "²⁷Al⁺ Quantum-Logic Clock with a Systematic Uncertainty below 10⁻¹⁸". Physical Review Letters. 123 (3) 033201. arXiv:1902.07694. Bibcode:2019PhRvL.123c3201B. doi:10.1103/PhysRevLett.123.033201. PMID 31386450. S2CID 119075546.
Huntemann, N.; Sanner, C.; Lipphardt, B.; Tamm, Chr. (8 February 2016). "Single-Ion Atomic Clock with 3×10⁻¹⁸ Systematic Uncertainty". Physical Review Letters. 116 (6) 063001. arXiv:1602.03908. Bibcode:2016PhRvL.116f3001H. doi:10.1103/PhysRevLett.116.063001. PMID 26918984. S2CID 19870627.
Leute, J.; Huntemann, N.; Lipphardt, B.; Tamm, Christian (3 February 2016). "Frequency Comparison of ¹⁷¹Yb⁺ Ion Optical Clocks at PTB and NPL via GPS PPP". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 63 (7): 981–985. arXiv:1507.04754. doi:10.1109/TUFFC.2016.2524988. PMID 26863657. S2CID 20466105.
Ren, Wei; Li, Tang; Qu, Qiuzhi; Wang, Bin; Li, Lin; Lü, Desheng; Chen, Weibiao; Liu, Liang (18 December 2020). "Development of a space cold atom clock". National Science Review. 7 (12): 1828–1836. doi:10.1093/nsr/nwaa215. ISSN 2095-5138. PMC 8288775. PMID 34691520.
Bothwell, Tobias; Kennedy, Colin J.; Aeppli, Alexander; Kedar, Dhruv; Robinson, John M.; Oelker, Eric; Staron, Alexander; Ye, Jun (2022). "Resolving the gravitational redshift across a millimetre-scale atomic sample". Nature. 602 (7897): 420–424. arXiv:2109.12238. Bibcode:2022Natur.602..420B. doi:10.1038/s41586-021-04349-7. PMID 35173346. S2CID 237940816.
Koller, S. B.; Grotti, J.; Vogt, St.; Al-Masoudi, A.; Dörscher, S.; Häfner, S.; Sterr, U.; Lisdat, Ch. (13 February 2017). "Transportable Optical Lattice Clock with 7×10⁻¹⁷ Uncertainty". Physical Review Letters. 118 (7) 073601. arXiv:1609.06183. doi:10.1103/PhysRevLett.118.073601. ISSN 0031-9007. PMID 28256845. S2CID 40822816.

ncbi.nlm.nih.gov

Ramsey, N. F. (September 1983). "History of Atomic Clocks". Journal of Research of the National Bureau of Standards. 88 (5): 301–320. doi:10.6028/jres.088.015. ISSN 0160-1741. PMC 6768155. PMID 34566107.
Nicholson, T. L.; Campbell, S. L.; Hutson, R. B.; Marti, G. E.; Bloom, B. J.; McNally, R. L.; Zhang, W.; Barrett, M. D.; Safronova, M. S.; Strouse, G. F.; Tew, W. L. (21 April 2015). "Systematic evaluation of an atomic clock at 2×10⁻¹⁸ total uncertainty". Nature Communications. 6 (1) 6896. arXiv:1412.8261. Bibcode:2015NatCo...6.6896N. doi:10.1038/ncomms7896. ISSN 2041-1723. PMC 4411304. PMID 25898253.
Pottie, Paul-Eric; Grosche, Gesine (19 August 2016). "A clock network for geodesy and fundamental science". Nature Communications. 7 12443. arXiv:1511.07735. Bibcode:2016NatCo...712443L. doi:10.1038/ncomms12443. PMC 4980484. PMID 27503795.
Ren, Wei; Li, Tang; Qu, Qiuzhi; Wang, Bin; Li, Lin; Lü, Desheng; Chen, Weibiao; Liu, Liang (18 December 2020). "Development of a space cold atom clock". National Science Review. 7 (12): 1828–1836. doi:10.1093/nsr/nwaa215. ISSN 2095-5138. PMC 8288775. PMID 34691520.

nist.gov (Global: 355^th place; English: 454^th place)

nist.gov

"NIST Launches a New U.S. Time Standard: NIST-F2 Atomic Clock". NIST. 3 April 2014 – via www.nist.gov.
"NIST Ion Clock Sets New Record for Most Accurate Clock in the World". Retrieved 17 November 2025.
"Optical Clocks: The Future of Time". Retrieved 17 November 2025.
NIST (31 December 2009). "Optical Frequency Combs". NIST. Retrieved 16 February 2022.
swenson (4 February 2010). "NIST's Second 'Quantum Logic Clock' Based on Aluminum Ion is Now World's Most Precise Clock". NIST. Retrieved 21 February 2022.
sarah.henderson@nist.gov (15 July 2019). "NIST's Quantum Logic Clock Returns to Top Performance". NIST. Retrieved 21 February 2022.
robin.materese@nist.gov (9 April 2019). "Second: The Future". NIST. Retrieved 20 February 2022.
"NIST launches a new US time standard: NIST-F2 atomic clock". NIST. nist.gov. 3 April 2014. Archived from the original on 6 April 2014. Retrieved 3 April 2014.
sarah.henderson@nist.gov (24 March 2021). "NIST Team Compares 3 Top Atomic Clocks With Record Accuracy Over Both Fiber and Air". NIST. Retrieved 16 February 2022.
swenson (29 December 1999). "NIST-F1 Cesium Fountain Clock". NIST. Retrieved 19 February 2022.
mweiss (26 August 2009). "NIST-F1 Cesium Fountain Atomic Clock". NIST. Retrieved 19 February 2022.
"NIST Launches a New U.S. Time Standard: NIST-F2 Atomic Clock". NIST. 3 April 2014. Archived from the original on 19 August 2016. Retrieved 13 July 2017.
andrew.novick@nist.gov (11 February 2010). "Help with WWVB Radio Controlled Clocks". NIST. Retrieved 15 February 2022.
lombardi (24 September 2009). "Radio Station WWV". NIST. Retrieved 16 February 2022.
sarah.henderson@nist.gov (16 February 2022). "JILA Atomic Clocks Measure Einstein's General Relativity at Millimeter Scale". NIST. Retrieved 17 February 2022.
mark.esser@nist.gov (18 June 2020). "Keeping Time at NIST". NIST. Retrieved 16 February 2022.

tf.nist.gov

Lombardi, M. A.; Heavner, T. P.; Jefferts, S. R. (2007). "NIST Primary Frequency Standards and the Realization of the SI Second" (PDF). Journal of Measurement Science. 2 (4): 74–89. Archived (PDF) from the original on 12 February 2021. Retrieved 24 October 2009.
Ye, J.; Schnatz, H.; Hollberg, L. W. (2003). "Optical frequency combs: From frequency metrology to optical phase control" (PDF). IEEE Journal of Selected Topics in Quantum Electronics. 9 (4): 1041–1058. Bibcode:2003IJSTQ...9.1041Y. doi:10.1109/JSTQE.2003.819109. Archived (PDF) from the original on 6 March 2016. Retrieved 25 February 2016.
"Chip-Scale Atomic Devices at NIST". NIST. 2007. Archived from the original on 7 January 2008. Retrieved 17 January 2008. Available on-line at: NIST.gov. Archived 7 January 2021 at the Wayback Machine
Allan, David W. Statistics of Atomic Frequency Standards, pp. 221–230. Proceedings of the IEEE, Vol. 54, No 2, February 1966.
J. A. Barnes, A. R. Chi, L. S. Cutler, D. J. Healey, D. B. Leeson, T. E. McGunigal, J. A. Mullen, W. L. Smith, R. Sydnor, R. F. C. Vessot, G. M. R. Winkler: Characterization of Frequency Stability, NBS Technical Note 394, 1970.
NIST (December 2007). "NIST Primary Frequency Standards and the Realization of the SI Second" (PDF). NCSL International Measure. 2: 77.
Michael A. Lombardi, "How Accurate is a Radio Controlled Clock?", Archived 7 January 2021 at the Wayback Machine, National Institute of Standards and Technology, 2010.

tf.boulder.nist.gov

Thomas P. Heavner; Elizabeth A. Donley; Filippo Levi; Giovanni Costanzo; Thomas E. Parker; Jon H. Shirley; Neil Ashby; Stephan Barlow; Steven R. Jefferts (May 2014). "First Accuracy Evaluation of NIST-F2" (PDF). Metrologia. 51 (3): 174–182. doi:10.1088/0026-1394/51/3/174.

npl.co.uk (Global: 8,830^th place; English: 8,644^th place)

npl.co.uk

"60 years of the Atomic Clock". National Physical Laboratory. Archived from the original on 17 October 2017. Retrieved 17 October 2017.

empir.npl.co.uk

National Physical Laboratory (2019). "OC18". National Physical laboratory.

nytimes.com (Global: 7^th place; English: 7^th place)

Belcher, David (1 November 2021). "Trying to Get Somewhere? An Atomic Clock May Be Helping". The New York Times. ISSN 0362-4331. Retrieved 15 February 2022.

obspm.fr (Global: 6,718^th place; English: 9,470^th place)

syrte.obspm.fr

"Optical fibre link opens a new era of time-frequency metrology, 19 August 2016". Archived from the original on 14 November 2016. Retrieved 13 November 2016.

optica.org (Global: low place; English: low place)

"Unprecedented optical clock network lays groundwork for redefining the second". Retrieved 18 December 2025.

optics.org (Global: low place; English: low place)

"NIST's ion clock claims record for 'most accurate in the world'". Retrieved 17 November 2025.

pdana.com (Global: low place; English: low place)

Dana, Peter H.; Penro, Bruce M. (July–August 1990). "The Role of GPS in Precise Time and Frequency Dissemination" (PDF). GPSworld. Archived (PDF) from the original on 15 December 2012. Retrieved 27 April 2014.

phys.org (Global: 1,283^rd place; English: 1,130^th place)

Laboratory, National Physical. "Accuracy of the NPL caesium fountain clock further improved". phys.org. Retrieved 20 February 2022.
Ahmed, Issam. "What the world's most accurate clock can tell us about Earth and the cosmos". phys.org. Retrieved 11 February 2022.

ptb.de (Global: 9,128^th place; English: low place)

Peik, E.; Tamm, Chr. (15 January 2003). "Nuclear laser spectroscopy of the 3.5 eV transition in ²²⁹Th" (PDF). Europhysics Letters. 61 (2): 181–186. Bibcode:2003EL.....61..181P. doi:10.1209/epl/i2003-00210-x. S2CID 250818523. Archived from the original (PDF) on 16 December 2013. Retrieved 11 September 2019.

qps.nl (Global: low place; English: low place)

confluence.qps.nl

"UTC to GPS Time Correction". qps.nl. Archived from the original on 21 March 2017. Retrieved 4 October 2015.

quantamagazine.org (Global: 6,413^th place; English: 4,268^th place)

"An Ultra-Precise Clock Shows How to Link the Quantum World With Gravity". Quanta Magazine. 25 October 2021. Retrieved 16 February 2022.

researchgate.net (Global: 120^th place; English: 125^th place)

Quessada, A.; Kovacich, R. P.; Courtillot, I.; Clairon, A.; Santarelli, G.; Lemonde, P. (2 April 2003). "The Dick effect for an optical frequency standard". Journal of Optics B: Quantum and Semiclassical Optics. 5 (2): S150 – S154. Bibcode:2003JOptB...5S.150Q. doi:10.1088/1464-4266/5/2/373.
Westergaard, P. G.; Lodewyck, J.; Lemonde, P. (March 2010). "Minimizing the Dick effect in an optical lattice clock". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 57 (3): 623–628. arXiv:0909.0909. Bibcode:2010ITUFF..57..623W. doi:10.1109/TUFFC.2010.1457. PMID 20211780. S2CID 10581032.

reuters.com (Global: 49^th place; English: 47^th place)

uk.reuters.com

"China puts final satellite for Beidou network into orbit – state media". Reuters. 23 June 2020. Archived from the original on 28 October 2020. Retrieved 23 June 2020.

revolutionized.com (Global: low place; English: low place)

"What Are Optical Clocks and Why Are They Important?". Revolutionalized. 20 July 2021. Retrieved 20 July 2021.

"Passive Hydrogen Maser (PHM)". Safran - Navigation & Timing. Archived from the original on 6 March 2019. Retrieved 30 January 2017.
"Rb Atomic Frequency Standard (RAFS)". safran-navigation-timing.com. Archived from the original on 6 November 2018. Retrieved 30 January 2017.

sci-news.com (Global: low place; English: 9,089^th place)

"2016 Gets Longer with Extra Second Added to New Year Countdown | Sci-News.com". Breaking Science News | Sci-News.com. 23 December 2016. Retrieved 20 February 2022.

sciencenews.org (Global: 3,410^th place; English: 2,939^th place)

"An atomic clock measured how general relativity warps time across a millimeter". Science News. 18 October 2021. Retrieved 22 February 2022.
Conover, Emily (4 September 2024). "A nuclear clock prototype hints at ultraprecise timekeeping". ScienceNews.

scitechdaily.com (Global: low place; English: low place)

University, Lancaster (11 May 2021). "Clock Experiment Shows a Fundamental Connection Between Energy Consumption and Accuracy". SciTechDaily. Retrieved 16 February 2022.

semanticscholar.org (Global: 11^th place; English: 8^th place)

api.semanticscholar.org

Ramsey, Norman F. (June 2006). "History of early atomic clocks". Metrologia. 42 (3): S1 – S3. doi:10.1088/0026-1394/42/3/s01. ISSN 0026-1394. S2CID 122631200.
Essen, L.; Parry, J. V. L. (1955). "An Atomic Standard of Frequency and Time Interval: A Cæsium Resonator". Nature. 176 (4476): 280–282. Bibcode:1955Natur.176..280E. doi:10.1038/176280a0. S2CID 4191481.
Essen, L.; Parry, J. V. L. (1955). "An Atomic Standard of Frequency and Time Interval: A Cæsium Resonator". Nature. 176 (4476): 280. Bibcode:1955Natur.176..280E. doi:10.1038/176280a0. S2CID 4191481. p.280.
Lodewyck, Jérôme (16 September 2019). "On a definition of the SI second with a set of optical clock transitions". Metrologia. 56 (5) 055009. arXiv:1911.05551. Bibcode:2019Metro..56e5009L. doi:10.1088/1681-7575/ab3a82. ISSN 0026-1394. S2CID 202129810.
Brewer, S. M.; Chen, J.-S.; Hankin, A. M.; Clements, E. R.; Chou, C. W.; Wineland, D. J.; Hume, D. B.; Leibrandt, D. R. (15 July 2019). "Al+27 Quantum-Logic Clock with a Systematic Uncertainty below 10⁻¹⁸". Physical Review Letters. 123 (3) 033201. arXiv:1902.07694. doi:10.1103/physrevlett.123.033201. ISSN 0031-9007. PMID 31386450. S2CID 119075546.
Bothwell, Tobias; Kennedy, Colin J.; Aeppli, Alexander; Kedar, Dhruv; Robinson, John M.; Oelker, Eric; Staron, Alexander; Ye, Jun (16 February 2022). "Resolving the gravitational redshift across a millimetre-scale atomic sample". Nature. 602 (7897): 420–424. arXiv:2109.12238. Bibcode:2022Natur.602..420B. doi:10.1038/s41586-021-04349-7. ISSN 0028-0836. PMID 35173346. S2CID 246902611.
Poli, N (2014). "Optical atomic clocks". La Rivista del Nuovo Cimento. 36 (12): 555. arXiv:1401.2378. Bibcode:2013NCimR..36..555P. doi:10.1393/ncr/i2013-10095-x. S2CID 118430700.
Santarelli, G.; Audoin, C.; Makdissi, A.; Laurent, P.; Dick, G.J.; Clairon, A. (1998). "Frequency stability degradation of an oscillator slaved to a periodically interrogated atomic resonator". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 45 (4): 887–894. Bibcode:1998ITUFF..45..887S. doi:10.1109/58.710548. PMID 18244242. S2CID 12303876.
Ludlow, A. D.; Boyd, M. M.; Ye, Jun; Peik, E.; Schmidt, P. O. (26 June 2015). "Optical atomic clocks". Reviews of Modern Physics. 87 (2): 637–701. arXiv:1407.3493. Bibcode:2015RvMP...87..637L. doi:10.1103/RevModPhys.87.637. S2CID 119116973.
Westergaard, P. G.; Lodewyck, J.; Lemonde, P. (March 2010). "Minimizing the Dick effect in an optical lattice clock". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 57 (3): 623–628. arXiv:0909.0909. Bibcode:2010ITUFF..57..623W. doi:10.1109/TUFFC.2010.1457. PMID 20211780. S2CID 10581032.
Beloy, Kyle; Bodine, Martha I.; Bothwell, Tobias; Brewer, Samuel M.; Bromley, Sarah L.; Chen, Jwo-Sy; Deschênes, Jean-Daniel; Diddams, Scott A.; Fasano, Robert J.; Fortier, Tara M.; Hassan, Youssef S. (25 March 2021). "Frequency ratio measurements at 18-digit accuracy using an optical clock network". Nature. 591 (7851): 564–569. Bibcode:2021Natur.591..564B. doi:10.1038/s41586-021-03253-4. ISSN 1476-4687. PMID 33762766. S2CID 232355391.
Peik, E.; Tamm, Chr. (15 January 2003). "Nuclear laser spectroscopy of the 3.5 eV transition in ²²⁹Th" (PDF). Europhysics Letters. 61 (2): 181–186. Bibcode:2003EL.....61..181P. doi:10.1209/epl/i2003-00210-x. S2CID 250818523. Archived from the original (PDF) on 16 December 2013. Retrieved 11 September 2019.
Campbell, C.; Radnaev, A.G.; Kuzmich, A.; Dzuba, V.A.; Flambaum, V.V.; Derevianko, A. (2012). "A single ion nuclear clock for metrology at the 19th decimal place". Phys. Rev. Lett. 108 (12) 120802. arXiv:1110.2490. Bibcode:2012PhRvL.108l0802C. doi:10.1103/PhysRevLett.108.120802. PMID 22540568. S2CID 40863227.
von der Wense, Lars; Seiferle, Benedict; Laatiaoui, Mustapha; Neumayr, Jürgen B.; Maier, Hans-Jörg; Wirth, Hans-Friedrich; Mokry, Christoph; Runke, Jörg; Eberhardt, Klaus; Düllmann, Christoph E.; Trautmann, Norbert G.; Thirolf, Peter G. (5 May 2016). "Direct detection of the ²²⁹Th nuclear clock transition". Nature. 533 (7601): 47–51. arXiv:1710.11398. Bibcode:2016Natur.533...47V. doi:10.1038/nature17669. PMID 27147026. S2CID 205248786.
Thielking, J.; Okhapkin, M.V.; Glowacki, P.; Meier, D.M.; von der Wense, L.; Seiferle, B.; Düllmann, C.E.; Thirolf, P.G.; Peik, E. (2018). "Laser spectroscopic characterization of the nuclear-clock isomer ^229mTh". Nature. 556 (7701): 321–325. arXiv:1709.05325. Bibcode:2018Natur.556..321T. doi:10.1038/s41586-018-0011-8. PMID 29670266. S2CID 4990345.
Masuda, T.; Yoshimi, A.; Fujieda, A.; Fujimoto, H.; Haba, H.; Hara, H.; Hiraki, T.; Kaino, H.; Kasamatsu, Y.; Kitao, S.; Konashi, K.; Miyamoto, Y.; Okai, K.; Okubo, S.; Sasao, N.; Seto, M.; Schumm, T.; Shigekawa, Y.; Suzuki, K.; Stellmer, S.; Tamasaku, K.; Uetake, S.; Watanabe, M.; Watanabe, T.; Yasuda, Y.; Yamaguchi, A.; Yoda, Y.; Yokokita, T.; Yoshimura, M.; Yoshimura, K. (12 September 2019). "X-ray pumping of the ²²⁹Th nuclear clock isomer". Nature. 573 (7773): 238–242. arXiv:1902.04823. Bibcode:2019Natur.573..238M. doi:10.1038/s41586-019-1542-3. PMID 31511686. S2CID 119083861.
Seiferle, B.; von der Wense, L.; Bilous, P.V.; Amersdorffer, I.; Lemell, C.; Libisch, F.; Stellmer, S.; Schumm, T.; Düllmann, C.E.; Pálffy, A.; Thirolf, P.G. (12 September 2019). "Energy of the ²²⁹Th nuclear clock transition". Nature. 573 (7773): 243–246. arXiv:1905.06308. Bibcode:2019Natur.573..243S. doi:10.1038/s41586-019-1533-4. PMID 31511684. S2CID 155090121.
Seiferle, Benedict; von der Wense, Lars; Thirolf, Peter G. (2017). "Lifetime measurement of the ²²⁹Th nuclear isomer". Physical Review Letters. 118 (4) 042501. arXiv:1801.05205. Bibcode:2017PhRvL.118d2501S. doi:10.1103/PhysRevLett.118.042501. PMID 28186791. S2CID 37518294. A half-life of 7±1 μs has been measured
National Physical Laboratory (2011). "When should we change the definition of the second?". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 369 (1953): 4109–4130. Bibcode:2011RSPTA.369.4109G. doi:10.1098/rsta.2011.0237. PMID 21930568. S2CID 6896025.
Gill, Patrick (28 October 2011). "When should we change the definition of the second?". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 369 (1953): 4109–4130. Bibcode:2011RSPTA.369.4109G. doi:10.1098/rsta.2011.0237. PMID 21930568. S2CID 6896025.
Essen, L; Donaldson, R W; Hope, E G; Bangham, M J (July 1973). "Hydrogen Maser Work at the National Physical Laboratory". Metrologia. 9 (3): 128–137. Bibcode:1973Metro...9..128E. doi:10.1088/0026-1394/9/3/004. S2CID 250828528.
Dupays, Arnaud; Beswick, Alberto; Lepetit, Bruno; Rizzo, Carlo (August 2003). "Proton Zemach radius from measurements of the hyperfine splitting of hydrogen and muonic hydrogen" (PDF). Physical Review A. 68 (5) 052503. arXiv:quant-ph/0308136. Bibcode:2003PhRvA..68e2503D. doi:10.1103/PhysRevA.68.052503. S2CID 3957861. Archived (PDF) from the original on 14 January 2019. Retrieved 26 September 2016.
Brewer, S.; Chen, J.-S.; Hankin, A.; Clements, E. (15 July 2019). "²⁷Al⁺ Quantum-Logic Clock with a Systematic Uncertainty below 10⁻¹⁸". Physical Review Letters. 123 (3) 033201. arXiv:1902.07694. Bibcode:2019PhRvL.123c3201B. doi:10.1103/PhysRevLett.123.033201. PMID 31386450. S2CID 119075546.
Huntemann, N.; Sanner, C.; Lipphardt, B.; Tamm, Chr. (8 February 2016). "Single-Ion Atomic Clock with 3×10⁻¹⁸ Systematic Uncertainty". Physical Review Letters. 116 (6) 063001. arXiv:1602.03908. Bibcode:2016PhRvL.116f3001H. doi:10.1103/PhysRevLett.116.063001. PMID 26918984. S2CID 19870627.
Leute, J.; Huntemann, N.; Lipphardt, B.; Tamm, Christian (3 February 2016). "Frequency Comparison of ¹⁷¹Yb⁺ Ion Optical Clocks at PTB and NPL via GPS PPP". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 63 (7): 981–985. arXiv:1507.04754. doi:10.1109/TUFFC.2016.2524988. PMID 26863657. S2CID 20466105.
Bothwell, Tobias; Kennedy, Colin J.; Aeppli, Alexander; Kedar, Dhruv; Robinson, John M.; Oelker, Eric; Staron, Alexander; Ye, Jun (2022). "Resolving the gravitational redshift across a millimetre-scale atomic sample". Nature. 602 (7897): 420–424. arXiv:2109.12238. Bibcode:2022Natur.602..420B. doi:10.1038/s41586-021-04349-7. PMID 35173346. S2CID 237940816.
Koller, S. B.; Grotti, J.; Vogt, St.; Al-Masoudi, A.; Dörscher, S.; Häfner, S.; Sterr, U.; Lisdat, Ch. (13 February 2017). "Transportable Optical Lattice Clock with 7×10⁻¹⁷ Uncertainty". Physical Review Letters. 118 (7) 073601. arXiv:1609.06183. doi:10.1103/PhysRevLett.118.073601. ISSN 0031-9007. PMID 28256845. S2CID 40822816.

smithsonianmag.com (Global: 503^rd place; English: 364^th place)

Fox, Alex. "New Atomic Clocks May Someday Redefine the Length of a Second". Smithsonian Magazine. Retrieved 16 February 2022.

spacecorp.ru (Global: low place; English: low place)

"GLONASS Interface Control Document, Navigation radiosignal In bands L1, L2 (ICD L1, L2 GLONASS), Russian Institute of Space Device Engineering, Edition 5.1, 2008" (PDF). Archived (PDF) from the original on 14 April 2016. Retrieved 2 October 2015.

symmetricom.com (Global: low place; English: low place)

"SA.45s CSAC Chip Scale Atomic Clock (archived version of the original pdf)" (PDF). 2011. Archived from the original (PDF) on 25 May 2013. Retrieved 12 June 2013.

thedefensepost.com (Global: 9,268^th place; English: 6,642^nd place)

"DARPA Aims for More Accurate Atomic Clock to Replace GPS". The Defense Post. 1 February 2022. Retrieved 15 February 2022.

thenextweb.com (Global: 1,356^th place; English: 870^th place)

Vleugels, Anouk (23 May 2021). "New experiment: Clocks consuming more energy are more accurate… 'cause thermodynamics". TNW | Science. Retrieved 16 February 2022.

timeanddate.com (Global: 1,373^rd place; English: 1,090^th place)

"How Do Atomic Clocks Work?". www.timeanddate.com. Retrieved 17 February 2022.

tuwien.at (Global: low place; English: low place)

Tiedau, J.; Okhapkin, M. V.; Zhang, K.; Thielking, J.; Zitzer, G.; Peik, E.; et al. (29 April 2024). "Laser Excitation of the Th-229 Nucleus" (PDF). Physical Review Letters. 132 (18) 182501. Bibcode:2024PhRvL.132r2501T. doi:10.1103/PhysRevLett.132.182501. PMID 38759160. The nuclear resonance for the Th⁴⁺ ions in Th:CaF₂ is measured at the wavelength 148.3821(5) nm, frequency 2020.409(7) THz, and the fluorescence lifetime in the crystal is 630(15) s, corresponding to an isomer half-life of 1740(50) s for a nucleus isolated in vacuum.

unoosa.org (Global: low place; English: low place)

"1 The Definition and Implementation of Galileo System Time (GST). ICG-4 WG-D on GNSS time scales. Jérôme Delporte. CNES – French Space Agency" (PDF). Archived (PDF) from the original on 6 November 2016. Retrieved 5 October 2015.
"GNSS Timescale Description" (PDF). Archived (PDF) from the original on 28 October 2020. Retrieved 5 October 2015.
"Definition and Realization of the System Time of COMPASS/BeiDou Navigation Satellite System, Chunhao Han, Beijing Global Information Center,(BGIC), Beijing, China" (PDF). Archived (PDF) from the original on 29 October 2020. Retrieved 5 October 2015.

ursi.org (Global: low place; English: low place)

Riehle, Fritz. "On Secondary Representations of the Second" (PDF). Physikalisch-Technische Bundesanstalt, Division Optics. Archived from the original (PDF) on 23 June 2015. Retrieved 22 June 2015.

uscg.gov (Global: low place; English: 9,986^th place)

navcen.uscg.gov

"NAVSTAR GPS User Equipment Introduction" (PDF). Archived (PDF) from the original on 21 October 2013. Retrieved 4 October 2015. Section 1.2.2
"NOTICE ADVISORY TO NAVSTAR USERS (NANU)". May 2017. Archived from the original on 28 May 2017. Retrieved 4 October 2015.

usenix.org (Global: 5,990^th place; English: 3,752^nd place)

Geng, Yilong; Liu, Shiyu; Yin, Zi; Naik, Ashish; Prabhakar, Balaji; Rosenblum, Mendel; Vahdat, Amin (2018). Exploiting a Natural Network Effect for Scalable, Fine-grained Clock Synchronization. 15th USENIX Symposium on Networked Systems Design and Implementation. pp. 81–94. ISBN 978-1-939133-01-4.

web.archive.org (Global: 1^st place; English: 1^st place)

"USNO Master Clock". Archived from the original on 7 December 2010. Retrieved 23 November 2010.
Lombardi, M. A.; Heavner, T. P.; Jefferts, S. R. (2007). "NIST Primary Frequency Standards and the Realization of the SI Second" (PDF). Journal of Measurement Science. 2 (4): 74–89. Archived (PDF) from the original on 12 February 2021. Retrieved 24 October 2009.
Sullivan, D. B. (2001). Time and frequency measurement at NIST: The first 100 years (PDF). IEEE International Frequency Control Symposium. NIST. pp. 4–17. Archived (PDF) from the original on 29 December 2019. Retrieved 1 May 2018.
"60 years of the Atomic Clock". National Physical Laboratory. Archived from the original on 17 October 2017. Retrieved 17 October 2017.
"President Piñera Receives ESO's First Atomic Clock". ESO Announcement. 15 November 2013. Archived from the original on 1 April 2014. Retrieved 20 November 2013.
Forman, Paul (1998). "Atomichron: The Atomic Clock from Concept to Commercial Product". Archived from the original on 21 October 2007. Retrieved 16 February 2022.
International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), ISBN 92-822-2213-6, archived (PDF) from the original on 4 June 2021, retrieved 16 December 2021
Ye, J.; Schnatz, H.; Hollberg, L. W. (2003). "Optical frequency combs: From frequency metrology to optical phase control" (PDF). IEEE Journal of Selected Topics in Quantum Electronics. 9 (4): 1041–1058. Bibcode:2003IJSTQ...9.1041Y. doi:10.1109/JSTQE.2003.819109. Archived (PDF) from the original on 6 March 2016. Retrieved 25 February 2016.
"SA.45s CSAC Chip Scale Atomic Clock (archived version of the original pdf)" (PDF). 2011. Archived from the original (PDF) on 25 May 2013. Retrieved 12 June 2013.
"Chip-Scale Atomic Devices at NIST". NIST. 2007. Archived from the original on 7 January 2008. Retrieved 17 January 2008. Available on-line at: NIST.gov. Archived 7 January 2021 at the Wayback Machine
Dick, G. J. (1987). Local oscillator induced instabilities in trapped ion frequency standards (PDF). Precise Time and Time Interval (PTTI) Conference. Redondo Beach. Archived from the original (PDF) on 19 October 2016.
"NIST launches a new US time standard: NIST-F2 atomic clock". NIST. nist.gov. 3 April 2014. Archived from the original on 6 April 2014. Retrieved 3 April 2014.
BIPM Annual Report on Time Activities (PDF). Vol. 15. International Bureau of Weights and Measures. 2020. p. 9. ISBN 978-92-822-2280-5. ISSN 1994-9405. Archived (PDF) from the original on 14 August 2021. Retrieved 16 June 2022.
"Optical fibre link opens a new era of time-frequency metrology, 19 August 2016". Archived from the original on 14 November 2016. Retrieved 13 November 2016.
"NIST Launches a New U.S. Time Standard: NIST-F2 Atomic Clock". NIST. 3 April 2014. Archived from the original on 19 August 2016. Retrieved 13 July 2017.
Peik, E.; Tamm, Chr. (15 January 2003). "Nuclear laser spectroscopy of the 3.5 eV transition in ²²⁹Th" (PDF). Europhysics Letters. 61 (2): 181–186. Bibcode:2003EL.....61..181P. doi:10.1209/epl/i2003-00210-x. S2CID 250818523. Archived from the original (PDF) on 16 December 2013. Retrieved 11 September 2019.
Peik, Ekkehard (25–27 September 2012). Concepts and Prospects for a Thorium-229 Nuclear Clock (PDF). EMMI Workshop: The ^229mTh Nuclear Isomer Clock. Darmstadt. Archived (PDF) from the original on 10 October 2021. Retrieved 2 December 2019.
Riehle, Fritz. "On Secondary Representations of the Second" (PDF). Physikalisch-Technische Bundesanstalt, Division Optics. Archived from the original (PDF) on 23 June 2015. Retrieved 22 June 2015.
"Unit of time (second)". SI Brochure. BIPM. 2014 [2006]. Archived from the original on 19 November 2011. Retrieved 23 June 2015.
"⁸⁷Rubidium BIPM document" (PDF). Archived (PDF) from the original on 23 September 2015. Retrieved 22 June 2015.
Dupays, Arnaud; Beswick, Alberto; Lepetit, Bruno; Rizzo, Carlo (August 2003). "Proton Zemach radius from measurements of the hyperfine splitting of hydrogen and muonic hydrogen" (PDF). Physical Review A. 68 (5) 052503. arXiv:quant-ph/0308136. Bibcode:2003PhRvA..68e2503D. doi:10.1103/PhysRevA.68.052503. S2CID 3957861. Archived (PDF) from the original on 14 January 2019. Retrieved 26 September 2016.
"⁸⁷Strontium BIPM document" (PDF). Archived (PDF) from the original on 4 March 2016. Retrieved 25 June 2015.
"²⁷Aluminum ion BIPM document". Archived from the original on 2 August 2022. Retrieved 9 December 2022.
"¹⁷¹Ytterbium 171 ion (642 THz) BIPM document". Archived from the original on 2 August 2022. Retrieved 9 December 2022.
"¹⁷¹Ytterbium 171 ion (688 THz) BIPM document". Archived from the original on 2 August 2022. Retrieved 9 December 2022.
"Global Positioning System". Gps.gov. Archived from the original on 30 July 2010. Retrieved 26 June 2010.
Allan, David W. (1997). "The Science of Timekeeping" (PDF). Application Note (1289). Hewlett Packard. Archived (PDF) from the original on 25 October 2012.
Dana, Peter H.; Penro, Bruce M. (July–August 1990). "The Role of GPS in Precise Time and Frequency Dissemination" (PDF). GPSworld. Archived (PDF) from the original on 15 December 2012. Retrieved 27 April 2014.
"GPS time accurate to 100 nanoseconds". Galleon. Archived from the original on 14 May 2012. Retrieved 12 October 2012.
"UTC to GPS Time Correction". qps.nl. Archived from the original on 21 March 2017. Retrieved 4 October 2015.
"NAVSTAR GPS User Equipment Introduction" (PDF). Archived (PDF) from the original on 21 October 2013. Retrieved 4 October 2015. Section 1.2.2
"NOTICE ADVISORY TO NAVSTAR USERS (NANU)". May 2017. Archived from the original on 28 May 2017. Retrieved 4 October 2015.
"Notice Advisory to Navstar Users (NANU) 2012034". GPS Operations Center. 30 May 2012. Archived from the original on 8 April 2013. Retrieved 2 July 2012.
"Time References in GNSS". navipedia.net. Archived from the original on 2 June 2018. Retrieved 2 October 2015.
"GLONASS Interface Control Document, Navigation radiosignal In bands L1, L2 (ICD L1, L2 GLONASS), Russian Institute of Space Device Engineering, Edition 5.1, 2008" (PDF). Archived (PDF) from the original on 14 April 2016. Retrieved 2 October 2015.
"Galileo begins serving the globe". European Space Agency. Archived from the original on 13 September 2019. Retrieved 15 December 2016.
"Galileo's contribution to the MEOSAR system". European Commission. Archived from the original on 9 July 2016. Retrieved 30 December 2015.
"European GNSS (Galileo) Open Service Signal-In-Space Operational Status Definition, Issue 1.0, September 2015" (PDF). Archived from the original (PDF) on 9 January 2017. Retrieved 3 October 2015.
"1 The Definition and Implementation of Galileo System Time (GST). ICG-4 WG-D on GNSS time scales. Jérôme Delporte. CNES – French Space Agency" (PDF). Archived (PDF) from the original on 6 November 2016. Retrieved 5 October 2015.
"Galileo's clocks". European Space Agency. Archived from the original on 29 August 2019. Retrieved 16 January 2017.
"Galileo Goes Live". European GNSS Agency. 15 December 2016. Archived from the original on 15 January 2021. Retrieved 1 February 2017.
"Galileo Initial Services – Open Service – Quarterly Performance Report Oct–Nov–Dec 2017" (PDF). European GNSS Service Centre. 28 March 2018. Archived (PDF) from the original on 26 August 2019. Retrieved 28 March 2017.
"Galileo Open Service and Search and Rescue – Quarterly Performance Reports, containing measured performance statistics". Archived from the original on 26 August 2019. Retrieved 3 March 2019.
"Passive Hydrogen Maser (PHM)". Safran - Navigation & Timing. Archived from the original on 6 March 2019. Retrieved 30 January 2017.
"Rb Atomic Frequency Standard (RAFS)". safran-navigation-timing.com. Archived from the original on 6 November 2018. Retrieved 30 January 2017.
"GNSS Timescale Description" (PDF). Archived (PDF) from the original on 28 October 2020. Retrieved 5 October 2015.
"ESA Adds System Time Offset to Galileo Navigation Message". insidegnss.com. Archived from the original on 28 March 2018. Retrieved 5 October 2015.
"Definition and Realization of the System Time of COMPASS/BeiDou Navigation Satellite System, Chunhao Han, Beijing Global Information Center,(BGIC), Beijing, China" (PDF). Archived (PDF) from the original on 29 October 2020. Retrieved 5 October 2015.
"China GPS rival Beidou starts offering navigation data". BBC. 27 December 2011. Archived from the original on 3 February 2012. Retrieved 22 June 2018.
"China's Beidou GPS-substitute opens to public in Asia". BBC. 27 December 2012. Archived from the original on 27 December 2012. Retrieved 27 December 2012.
Varma, K. J. M. (27 December 2018). "China's BeiDou navigation satellite, rival to US GPS, starts global services". livemint.com. Archived from the original on 27 December 2018. Retrieved 27 December 2018.
"China puts final satellite for Beidou network into orbit – state media". Reuters. 23 June 2020. Archived from the original on 28 October 2020. Retrieved 23 June 2020.
Landau, Elizabeth (27 April 2015). "Deep Space Atomic Clock". NASA. Archived from the original on 10 December 2015. Retrieved 29 April 2015.
Michael A. Lombardi, "How Accurate is a Radio Controlled Clock?", Archived 7 January 2021 at the Wayback Machine, National Institute of Standards and Technology, 2010.

wired.com (Global: 193^rd place; English: 152^nd place)

Mann, Adam. "How the U.S. Built the World's Most Ridiculously Accurate Atomic Clock". Wired. ISSN 1059-1028. Retrieved 15 February 2022.
Chen, Sophia. "These Physicists Watched a Clock Tick for 14 Years Straight". Wired. ISSN 1059-1028. Retrieved 15 February 2022.

worldcat.org (Global: 5^th place; English: 5^th place)

search.worldcat.org

Ramsey, Norman F. (June 2006). "History of early atomic clocks". Metrologia. 42 (3): S1 – S3. doi:10.1088/0026-1394/42/3/s01. ISSN 0026-1394. S2CID 122631200.
Rabi, I. I. (15 April 1937). "Space Quantization in a Gyrating Magnetic Field". Physical Review. 51 (8): 652–654. Bibcode:1937PhRv...51..652R. doi:10.1103/physrev.51.652. ISSN 0031-899X.
Rabi, I. I.; Zacharias, J. R.; Millman, S.; Kusch, P. (15 February 1938). "A New Method of Measuring Nuclear Magnetic Moment". Physical Review. 53 (4): 318. Bibcode:1938PhRv...53..318R. doi:10.1103/physrev.53.318. ISSN 0031-899X.
Ramsey, N. F. (September 1983). "History of Atomic Clocks". Journal of Research of the National Bureau of Standards. 88 (5): 301–320. doi:10.6028/jres.088.015. ISSN 0160-1741. PMC 6768155. PMID 34566107.
Hellwig, Helmut; Evenson, Kenneth M.; Wineland, David J. (December 1978). "Time, frequency and physical measurement". Physics Today. 31 (12): 23–30. Bibcode:1978PhT....31l..23H. doi:10.1063/1.2994867. ISSN 0031-9228.
Lodewyck, Jérôme (16 September 2019). "On a definition of the SI second with a set of optical clock transitions". Metrologia. 56 (5) 055009. arXiv:1911.05551. Bibcode:2019Metro..56e5009L. doi:10.1088/1681-7575/ab3a82. ISSN 0026-1394. S2CID 202129810.
Nicholson, T. L.; Campbell, S. L.; Hutson, R. B.; Marti, G. E.; Bloom, B. J.; McNally, R. L.; Zhang, W.; Barrett, M. D.; Safronova, M. S.; Strouse, G. F.; Tew, W. L. (21 April 2015). "Systematic evaluation of an atomic clock at 2×10⁻¹⁸ total uncertainty". Nature Communications. 6 (1) 6896. arXiv:1412.8261. Bibcode:2015NatCo...6.6896N. doi:10.1038/ncomms7896. ISSN 2041-1723. PMC 4411304. PMID 25898253.
Brewer, S. M.; Chen, J.-S.; Hankin, A. M.; Clements, E. R.; Chou, C. W.; Wineland, D. J.; Hume, D. B.; Leibrandt, D. R. (15 July 2019). "Al+27 Quantum-Logic Clock with a Systematic Uncertainty below 10⁻¹⁸". Physical Review Letters. 123 (3) 033201. arXiv:1902.07694. doi:10.1103/physrevlett.123.033201. ISSN 0031-9007. PMID 31386450. S2CID 119075546.
Bothwell, Tobias; Kennedy, Colin J.; Aeppli, Alexander; Kedar, Dhruv; Robinson, John M.; Oelker, Eric; Staron, Alexander; Ye, Jun (16 February 2022). "Resolving the gravitational redshift across a millimetre-scale atomic sample". Nature. 602 (7897): 420–424. arXiv:2109.12238. Bibcode:2022Natur.602..420B. doi:10.1038/s41586-021-04349-7. ISSN 0028-0836. PMID 35173346. S2CID 246902611.
Mann, Adam. "How the U.S. Built the World's Most Ridiculously Accurate Atomic Clock". Wired. ISSN 1059-1028. Retrieved 15 February 2022.
BIPM Annual Report on Time Activities (PDF). Vol. 15. International Bureau of Weights and Measures. 2020. p. 9. ISBN 978-92-822-2280-5. ISSN 1994-9405. Archived (PDF) from the original on 14 August 2021. Retrieved 16 June 2022.
Beloy, Kyle; Bodine, Martha I.; Bothwell, Tobias; Brewer, Samuel M.; Bromley, Sarah L.; Chen, Jwo-Sy; Deschênes, Jean-Daniel; Diddams, Scott A.; Fasano, Robert J.; Fortier, Tara M.; Hassan, Youssef S. (25 March 2021). "Frequency ratio measurements at 18-digit accuracy using an optical clock network". Nature. 591 (7851): 564–569. Bibcode:2021Natur.591..564B. doi:10.1038/s41586-021-03253-4. ISSN 1476-4687. PMID 33762766. S2CID 232355391.
Ren, Wei; Li, Tang; Qu, Qiuzhi; Wang, Bin; Li, Lin; Lü, Desheng; Chen, Weibiao; Liu, Liang (18 December 2020). "Development of a space cold atom clock". National Science Review. 7 (12): 1828–1836. doi:10.1093/nsr/nwaa215. ISSN 2095-5138. PMC 8288775. PMID 34691520.
Belcher, David (1 November 2021). "Trying to Get Somewhere? An Atomic Clock May Be Helping". The New York Times. ISSN 0362-4331. Retrieved 15 February 2022.
Chen, Sophia. "These Physicists Watched a Clock Tick for 14 Years Straight". Wired. ISSN 1059-1028. Retrieved 15 February 2022.
Koller, S. B.; Grotti, J.; Vogt, St.; Al-Masoudi, A.; Dörscher, S.; Häfner, S.; Sterr, U.; Lisdat, Ch. (13 February 2017). "Transportable Optical Lattice Clock with 7×10⁻¹⁷ Uncertainty". Physical Review Letters. 118 (7) 073601. arXiv:1609.06183. doi:10.1103/PhysRevLett.118.073601. ISSN 0031-9007. PMID 28256845. S2CID 40822816.

Atomic clock (English Wikipedia)

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