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# Making optical atomic clocks more stable with 10−16-level laser stabilization

## Abstract

The superb precision of an atomic clock is derived from its stability. Atomic clocks based on optical (rather than microwave) frequencies are attractive because of their potential for high stability, which scales with operational frequency. Nevertheless, optical clocks have not yet realized this vast potential, due in large part to limitations of the laser used to excite the atomic resonance. To address this problem, we demonstrate a cavity-stabilized laser system with a reduced thermal noise floor, exhibiting a fractional frequency instability of 2 × 10−16. We use this laser as a stable optical source in a ytterbium optical lattice clock to resolve an ultranarrow 1 Hz linewidth for the 518 THz clock transition. With the stable laser source and the signal-to-noise ratio afforded by the ytterbium optical clock, we dramatically reduce key stability limitations of the clock, and make measurements consistent with a clock instability of 5 × 10−16.

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## Acknowledgements

The authors acknowledge support regarding optical frequency comb measurements from S. Diddams, T. Fortier and M. Kirchner, optical cavity measurement and equipment loan from J. Bergquist, T. Rosenband and C. Chou, and useful discussions with J. Bergquist and G. Santarelli. The authors also thank L. Hollberg for design guidance and useful discussions. Y.Y.J. and L.S.M. acknowledge support from the National Basic Research Program of China (grant no. 2010CB922903) and the Science and Technology Commission of Shanghai Municipality (grant no. 07JC14019).

## Author information

Authors

### Contributions

Y.Y.J., A.D.L., N.D.L., and J.A.S. carried out the laser frequency or optical clock measurements reported here. Y.Y.J. designed and constructed many aspects of the stable cavity system and made many of the laser frequency measurements. R.W.F. carried out thermal design simulations and measurements. A.D.L. and N.D.L. designed and constructed many aspects of the stable cavity system. A.D.L., L.S.M., and C.W.O. supervised this work. All authors contributed to the final manuscript.

### Corresponding author

Correspondence to A. D. Ludlow.

## Ethics declarations

### Competing interests

The authors declare no competing financial interests.

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Reprints and Permissions

Jiang, Y., Ludlow, A., Lemke, N. et al. Making optical atomic clocks more stable with 10−16-level laser stabilization. Nature Photon 5, 158–161 (2011). https://doi.org/10.1038/nphoton.2010.313

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• DOI: https://doi.org/10.1038/nphoton.2010.313

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