Safronova, M. S. et al. Search for new physics with atoms and molecules. Rev. Mod. Phys. 90, 025008 (2018).
Google Scholar
Ludlow, A. D., Boyd, M. M., Ye, J., Peik, E. & Schmidt, P. O. Optical atomic clocks. Rev. Mod. Phys. 87, 637–701 (2015).
Google Scholar
Rosenband, T. et al. Frequency ratio of Al+ and Hg+ single-ion optical clocks; metrology at the 17th decimal place. Science 319, 1808–1812 (2008).
Google Scholar
Nemitz, N. et al. Frequency ratio of Yb and Sr clocks with 5 × 10−17 uncertainty at 150 seconds averaging time. Nat. Photon. 10, 258–261 (2016).
Google Scholar
Dörscher, S. et al. Optical frequency ratio of a 171Yb+ single-ion clock and a 87Sr lattice clock. Preprint at https://arXiv.org/abs/2009.05470 (2020).
Brewer, S. M. et al. An 27Al+ quantum-logic clock with systematic uncertainty below 10−18. Phys. Rev. Lett. 123, 033201 (2019).
Google Scholar
Bothwell, T. et al. JILA SrI optical lattice clock with uncertainty of 2.0 × 10−18. Metrologia 56, 065004 (2019).
Google Scholar
McGrew, W. F. et al. Atomic clock performance enabling geodesy below the centimetre level. Nature 564, 87–90 (2018).
Google Scholar
Van Tilburg, K., Leefer, N., Bougas, L. & Budker, D. Search for ultralight scalar dark matter with atomic spectroscopy. Phys. Rev. Lett. 115, 011802 (2015).
Google Scholar
Hees, A., Guéna, J., Abgrall, M., Bize, S. & Wolf, P. Searching for an oscillating massive scalar field as a dark matter candidate using atomic hyperfine frequency comparisons. Phys. Rev. Lett. 117, 061301 (2016).
Google Scholar
Foreman, S. M. et al. Coherent optical phase transfer over a 32-km fiber with 1s instability at 10−17. Phys. Rev. Lett. 99, 153601 (2007).
Google Scholar
Sinclair, L. C. et al. Comparing optical oscillators across the air to milliradians in phase and 10−17 in frequency. Phys. Rev. Lett. 120, 050801 (2018).
Google Scholar
Bodine, M. I. et al. Optical atomic clock comparison through turbulent air. Preprint at https://arXiv.org/abs/2006.01306 (2020).
Mehlstäubler, T. E., Grosche, G., Lisdat, C., Schmidt, P. O. & Denker, H. Atomic clocks for geodesy. Rep. Prog. Phys. 81, 064401 (2018).
Google Scholar
Riehle, F., Gill, P., Arias, F. & Robertsson, L. The CIPM list of recommended frequency standard values: guidelines and procedures. Metrologia 55, 188–200 (2018).
Google Scholar
Nicholson, T. L. et al. Systematic evaluation of an atomic clock at 2 × 10−18 total uncertainty. Nat. Commun. 6, 6896 (2015).
Google Scholar
Huntemann, N., Sanner, C., Lipphardt, B., Tamm, Chr. & Peik, E. Single-ion atomic clock with 3 × 10−18 systematic uncertainty. Phys. Rev. Lett. 116, 063001 (2016).
Google Scholar
Sanner, C. et al. Optical clock comparison for Lorentz symmetry testing. Nature 567, 204–208 (2019).
Google Scholar
Takamoto, M. et al. Test of general relativity by a pair of transportable optical lattice clocks. Nat. Photon. 14, 411–415 (2020).
Google Scholar
Godun, R. M. et al. Frequency ratio of two optical clock transitions in 171Yb+ and constraints on the time variation of fundamental constants. Phys. Rev. Lett. 113, 210801 (2014).
Google Scholar
Takamoto, M. et al. Frequency ratios of Sr, Yb, and Hg based optical lattice clocks and their applications. C.R. Phys. 16, 489–498 (2015).
Google Scholar
Tyumenev, R. et al. Comparing a mercury optical lattice clock with microwave and optical frequency standards. New J. Phys. 18, 113002 (2016).
Google Scholar
Ohmae, N., Bregolin, F., Nemitz, N. & Katori, H. Direct measurement of the frequency ratio for Hg and Yb optical lattice clocks and closure of the Hg/Yb/Sr loop. Opt. Express 28, 15112–15121 (2020).
Google Scholar
Lange, R. et al. Improved limits for violations of local position invariance from atomic clock comparisons. Preprint at https://arXiv.org/abs/2010.06620 (2020).
Riehle, F. Optical clock networks. Nat. Photon. 11, 25–31 (2017).
Google Scholar
Lisdat, C. et al. A clock network for geodesy and fundamental science. Nat. Commun. 7, 12443 (2016).
Google Scholar
Delehaye, M. & Lacroûte, C. Single-ion, transportable optical atomic clocks. J. Mod. Opt. 65, 622–639 (2018).
Google Scholar
Grotti, J. et al. Geodesy and metrology with a transportable optical clock. Nat. Phys. 14, 437–441 (2018).
Google Scholar
Dehmelt, H. G. Monoion oscillator as potential ultimate laser frequency standard. IEEE Trans. Instrum. Meas. IM-31, 83–87 (1982).
Google Scholar
Hall, J. L., Zhu, M. & Buch, P. Prospects for using laser-prepared atomic fountains for optical frequency standards applications. J. Opt. Soc. Am. B 6, 2194–2205 (1989).
Google Scholar
Itano, W. M. et al. Quantum projection noise: population fluctuations in two-level systems. Phys. Rev. A 47, 3554–3570 (1993).
Google Scholar
Oelker, E. et al. Demonstration of 4.8 × 10−17 stability at 1s for two independent optical clocks. Nat. Photon. 13, 714–719 (2019).
Google Scholar
Fortier, T. & Baumann, E. 20 years of developments in optical frequency comb technology and applications. Commun. Phys. 2, 153 (2019); correction 3, 85 (2020).
Leopardi, H. et al. Single-branch Er:fiber frequency comb for precision optical metrology with 10−18 fractional instability. Optica 4, 879–885 (2017).
Google Scholar
Fortier, T. M., Bartels, A. & Diddams, S. A. Octave-spanning Ti:sapphire laser with a repetition rate >1 GHz for optical frequency measurements and comparisons. Opt. Lett. 31, 1011–1013 (2006).
Google Scholar
Deschênes, J.-D. et al. Synchronization of distant optical clocks at the femtosecond level. Phys. Rev. X 6, 021016 (2016).
van Westrum, D. Geodetic Survey of NIST and JILA Clock Laboratories. NOAA Technical Report NOS NGS 77 (NOAA, 2019).
Gelman, A. et al. Bayesian Data Analysis 3rd edn (Chapman & Hall/CRC Texts in Statistical Science) (CRC Press, 2014).
Koepke, A., Lafarge, T., Possolo, A. & Toman, B. Consensus building for interlaboratory studies, key comparisons, and meta-analysis. Metrologia 54, S34–S62 (2017).
Google Scholar
Stalnaker, J. E. et al. Optical-to-microwave frequency comparison with fractional uncertainty of 10−15. Appl. Phys. B 89, 167–176 (2007).
Google Scholar
Rosenband, T. et al. Alpha-dot or not: comparison of two single atom optical clocks. In Proceedings of the 7th Symposium on Frequency Standards and Metrology (ed. Maleki, L.) 20–33 (World Scientific, 2009).
Riehle, F. Towards a redefinition of the second based on optical atomic clocks. C.R. Phys. 16, 506–515 (2015).
Google Scholar
Gill, P. When should we change the definition of the second? Phil. Trans. R. Soc. A 369, 4109–4130 (2011).
Google Scholar
Campbell, G. K. et al. The absolute frequency of the 87 Sr optical clock transition. Metrologia 45, 539–548 (2008).
Google Scholar
Lemke, N. D. et al. Spin-1/2 optical lattice clock. Phys. Rev. Lett. 103, 063001 (2009).
Google Scholar
Pizzocaro, M. et al. Absolute frequency measurement of the 1S0–3P0 transition of 171Yb. Metrologia 54, 102–112 (2017).
Google Scholar
Lodewyck, J. et al. Optical to microwave clock frequency ratios with a nearly continuous strontium optical lattice clock. Metrologia 53, 1123–1130 (2016).
Google Scholar
Grebing, C. et al. Realization of a timescale with an accurate optical lattice clock. Optica 3, 563–569 (2016).
Google Scholar
McGrew, W. F. et al. Towards the optical second: verifying optical clocks at the SI limit. Optica 6, 448–454 (2019).
Google Scholar
Akamatsu, D. et al. Frequency ratio measurement of 171 Yb and 87Sr optical lattice clocks. Opt. Express 22, 7898–7905 (2014).
Google Scholar
Hachisu, H., Petit, G., Nakagawa, F., Hanado, Y. & Ido, T. SI-traceable measurement of an optical frequency at the low 10−16 level without a local primary standard. Opt. Express 25, 8511–8523 (2017).
Google Scholar
Kim, H. et al. Improved absolute frequency measurement of the 171Yb optical lattice clock at KRISS relative to the SI second. Jpn. J. Appl. Phys. 56, 050302 (2017).
Google Scholar
Centers, G. P. et al. Stochastic fluctuations of bosonic dark matter. Preprint at https://arXiv.org/abs/1905.13650 (2019).
Hui, L., Ostriker, J. P., Tremaine, S. & Witten, E. Ultralight scalars as cosmological dark matter. Phys. Rev. D 95, 043541 (2017).
Google Scholar
Ma, L.-S., Jungner, P., Ye, J. & Hall, J. L. Delivering the same optical frequency at two places: accurate cancellation of phase noise introduced by an optical fiber or other time-varying path. Opt. Lett. 19, 1777–1779 (1994).
Google Scholar
Newbury, N. R., Williams, P. A. & Swann, W. C. Coherent transfer of an optical carrier over 251 km. Opt. Lett. 32, 3056–3058 (2007).
Google Scholar
Nemitz, N., Jørgensen, A. A., Yanagimoto, R., Bregolin, F. & Katori, H. Modeling light shifts in optical lattice clocks. Phys. Rev. A 99, 033424 (2019).
Google Scholar
Brown, R. C. et al. Hyperpolarizability and operational magic wavelength in an optical lattice clock. Phys. Rev. Lett. 119, 253001 (2017).
Google Scholar
Katori, H., Ovsiannikov, V. D., Marmo, S. I. & Palchikov, V. G. Strategies for reducing the light shift in atomic clocks. Phys. Rev. A 91, 052503 (2015).
Google Scholar
Mohr, P. J., Newell, D. B. & Taylor, B. N. Codata recommended values of the fundamental physical constants: 2014. Rev. Mod. Phys. 88, 035009 (2016).
Google Scholar
Su, Y.-S. & Yajima, M. R2jags: using R to run ‘JAGS’. https://cran.r-project.org/web/packages/R2jags/index.html (2015).
Geweke, J. Evaluating the accuracy of sampling-based approaches to calculating posterior moments. In Bayesian Statistics 4: Proceedings of the Fourth Valencia International Meeting (eds Bernado, J. M. et al) 641–649 (Clarendon, 1992).
Fuller, W. A. Measurement Error Models (Wiley & Sons, 1987).
Carroll, R. J., Ruppert, D., Stefanski, L. A. & Crainiceanu, C. M. Measurement Error in Nonlinear Models — A Modern Perspective 2nd edn (Chapman & Hall/CRC Texts in Statistical Science) (CRC Press, 2006).
Wcisło, P. et al. New bounds on dark matter coupling from a global network of optical atomic clocks. Sci. Adv. 4, eaau4869 (2018).
Google Scholar
Kennedy, C. J. et al. Precision metrology meets cosmology: improved constraints on ultralight dark matter from atom-cavity frequency comparisons. Phys. Rev. Lett. 125, 201302 (2020).
Google Scholar