Atomic clock (English Wikipedia)

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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.
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.
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.
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
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.
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.
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: $𝜈 Th = ⁠ 1 / 6 ⁠ (𝜈 a + 2 𝜈 b + 2 𝜈 c + 𝜈 d) = 2020407384335 (2) kHz$ .
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.

af.mil (Global: 414^th place; English: 225^th place)

gps.afspc.af.mil

"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: 5,715^th place; English: 5,215^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: 1,264^th place; English: 951^st 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: 1,143^rd place; English: 973^rd 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: 49^th place; English: 31^st 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.
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
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 (2,020,407.3(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: $𝜈 Th = ⁠ 1 / 6 ⁠ (𝜈 a + 2 𝜈 b + 2 𝜈 c + 𝜈 d) = 2020407384335 (2) kHz$ .
Toscani De Col, Luca; et al. (3 June 2026). "A thorium-229 optical nuclear clock with feedback loop". arXiv:2606.04997 [physics.atom-ph].
Huang, Beichen; et al. (7 June 2026). "A nuclear clock based on ²²⁹Th". arXiv:2606.08870 [physics.atom-ph].
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.
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Atomic clock (English Wikipedia)

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