[1] McGrew W F, Zhang X, Fasano R J, Schäffer S A, Beloy K, Nicolodi D, Brown R C, Hinkley N, Milani G, Schioppo M, Yoon T H and Ludlow A D 2018 Nature 564 87 [2] Brewer S M, Chen J S, Hankin A M, Clements E R, Chou C W, Wineland D J, Hume D B and Leibrandt D R 2019 Phys. Rev. Lett. 123 033201 [3] Oelker E, Hutson R B, Kennedy C J, Sonderhouse L, Bothwell T, Goban A, Kedar D, Sanner C, Robinson J M, Marti G E, Matei D G, Legero T, Giunta M, Holzwarth R, Riehle F, Sterr U and Ye J 2019 Nat. Photonics 13 714 [4] Huntemann N, Sanner C, Lipphardt B, Tamm C and Peik E 2016 Phys. Rev. Lett. 116 063001 [5] Takamoto M, Ushijima I, Ohmae N, Yahagi T, Kokado K, Shinkai H and Katori H 2020 Nat. Photonics 14 411 [6] Sanner C, Huntemann N, Lange R, Tamm C, Peik E, Safronova M S and Porsev S G 2019 Nature 567 204 [7] Chou C W, Hume D B, Rosenband T and Wineland D J 2010 Science 329 1630 [8] Beloy K, Bodine M I, Bothwell T, et al. 2021 Nature 591 564 [9] Wcisƚo P, Ablewski P, Beloy K, Bilicki S, Bober M, Brown R, Fasano R, Ciuryƚo R, Hachisu H, Ido T, Lodewyck J, Ludlow A, McGrew W, Morzyński P, Nicolodi D, Schioppo M, Sekido M, Le Targat R, Wolf P, Zhang X, Zjawin B and Zawada M 2018 Sci. Adv. 4 eaau4869 [10] Bothwell T, Kennedy C J, Aeppli A, Kedar D, Robinson J M, Oelker E, Staron A and Ye J 2022 Nature 602 420 [11] Kolkowitz S, Pikovski I, Langellier N, Lukin M D, Walsworth R L and Ye J 2017 Phys. Rev. D 94 124043 [12] https://www.bipm.org/documents/20126/35554894/CCTF+Strategy/7cf0f648-2afe-d15c-0909-1f03406bbb8f [13] CCTF 2021 Roadmap towards the redefinition of the SI second [14] Ai D, Qiao H, Zhang S, Luo L M, Sun C Y, Zhang S, Peng C Q, Qi Q C, Jin T Y, Zhou M and Xu X Y 2020 Chin. Phys. B 29 090601 [15] Katori H, Takamoto M, Pal'chikov V G and Ovsiannikov V D 2003 Phys. Rev. Lett. 91 173005 [16] Brown R C, Phillips N B, Beloy K, McGrew W F, Schioppo M, Fasano R J, Milani G, Zhang X, Hinkley N, Leopardi H, Yoon T H, Nicolodi D, Fortier T M and Ludlow A D 2017 Phys. Rev. Lett. 119 253001 [17] Nemitz N, Jorgensen A A, Yanagimoto R, Bregolin F and Katori H 2019 Phys. Rev. A 99 033424 [18] Ushijima I, Takamoto M and Katori H 2018 Phys. Rev. Lett. 121 263202 [19] Kim K, Aeppli A, Bothwell T and Ye J 2023 Phys. Rev. Lett. 130 113203 [20] Kim H, Heo M S, Park C Y, Yu D H and Lee W K 2021 Metrologia 58 055007 [21] Pizzocaro M, Bregolin F, Barbieri P, Rauf B, Levi F and Calonico D 2020 Metrologia 57 035007 [22] Koller S B, Grotti J, Vogt S T, Al-Masoudi A, Dörscher S, Häfner S, Sterr U and Lisdat C H 2017 Phys. Rev. Lett. 118 073601 [23] Zeng M, Huang Y, Zhang B, Hao Y, Ma Z, Hu R, Zhang H, Chen Z, Wang M, Guan H and Gao K 2023 Phys. Rev. Appl. 19 064004 [24] Yan W, Yao Y, Sun Y, Chad H W, Jiang Y and Ma L 2019 Chin. Opt. Lett. 17 040201 [25] Sun Y, Yao Y, Hao Y, Yu H, Jiang Y and Ma L 2020 Chin. Opt. Lett. 18 070201 [26] Fasano R J, Chen Y J, McGrew W F, Brand W J, Fox R and Ludlow A D 2021 Phys. Rev. Appl. 15 044016 [27] Lemonde P and Wolf P 2005 Phys. Rev. A 72 033409 [28] Ye J 1997 Ultrasensitive high resolution laser spectroscopy and its application to optical frequency standards (PhD thesis) [29] Drever R W P, Hall J L, Kowalski F V, Hough J, Ford G M, Munley A J and Ward H 1983 Appl. Phys. B 31 97 [30] Hao Y, Yao Y, Shi H, Yu H, Jiang Y and Ma L 2022 Chin. Opt. Lett. 20 120201 [31] Itano W M, Bergquist J C, Bollinger J J, Gilligan J M, Heinzen D J, Moore F L, Raizen M G and Wineland D J 2002 Phys. Rev. A 47 3554 [32] Blatt S, Thomsen J W, Campbell G K, Ludlow A D, Swallows M D, Martin M J, Boyd M M and Ye J 2009 Phys. Rev. A 80 052703 [33] Jiang Y Y, Ludlow A D, Lemke N D, Fox R W, Sherman J A, Ma L S and Oates C W 2011 Nat. Photonics 5 158 [34] Lu B, Su Z, Yang T, Lin Y, Wang Q, Li Y, Meng F, Lin B, Li T and Fang Z 2022 Chin. Phys. Lett. 39 080601 [35] Pizzocaro M, Thoumany P, Rauf B, Bregolin F, Milani G, Clivati C, Costanzo G A, Levi F and Calonico D 2017 Metrologia 54 102 |