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Conference on Lasers and Electro-Optics

10-18 Optical Atomic Clock Comparisons within the Boulder Atomic Clock Network

Nicholas V. Nardelli, K. Beloy, Martha I. Bodine, Tobias Bothwell, Samuel M. Brewer, Sarah Bromley, J. Chen, Ethan Clements, Jean-Daniel Deschênes, Scott A. Diddams, Robert Fasano, Tara M. Fortier, Youssef S. Hassan, David B. Hume, Dhruv Kedar, Colin J. Kennedy, Isaac H. Khader, May E. Kim, A. Koepke, David R. Leibrandt, Holly Leopardi, Andrew D. Ludlow, William F. McGrew, William R. Milner, Nathan R. Newbury, Daniele Nicolodi, Eric Glenn Oelker, T.E. Parker, John Martin Robinson, Stefan Alaric Schäffer, Jeff A. Sherman, Laura C. Sinclair, Lindsay Sonderhouse, William C. Swann, David J. Wineland, Jian Yao, J. Ye, Xiaogang Zhang

Published Jan 1, 2020• 0 citations
Publisher

Abstract

We demonstrate optical frequency comparison of the 171Yb, 27Al+ and 87Sr atomic clocks with measurement uncertainties below 1 part in 1017, and discuss how phase-coherent and synchronous clock comparisons can be used to improve measurement stability.
DOI
10.1364/cleo_si.2020.sth3g.3

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Atomic clocks occupy a unique position in measurement science, exhibiting higher accuracy than any other measurement standard and underpinning six out of seven base units in the SI system. By exploiting higher resonance frequencies, optical atomic clocks now achieve greater stability and lower frequency uncertainty than existing primary standards. Here, we report frequency ratios of the 27^{27}27Al+^++, 171^{171}171Yb and 87^{87}87Sr optical clocks in Boulder, Colorado, measured across an optical network spanned by both fiber and free-space links. These ratios have been evaluated with measurement uncertainties between 6×10−186\times10^{-18}6×10−18 and 8×10−188\times10^{-18}8×10−18, making them the most accurate reported measurements of frequency ratios to date. This represents a critical step towards redefinition of the SI second and future applications such as relativistic geodesy and tests of fundamental physics.
Atomic clock frequency ratios with fractional uncertainty ≤3.2×10−18\leq 3.2 \times 10^{-18}≤3.2×10−18
We report high-precision frequency ratio measurements between optical atomic clocks based on 27^{27}27Al+^++, 171^{171}171Yb, and 87^{87}87Sr. With total fractional uncertainties at or below 3.2×10−183.2 \times 10^{-18}3.2×10−18, these measurements meet an important milestone criterion for redefinition of the second in the International System of Units. Discrepancies in 87^{87}87Sr ratios at approximately 1×10−161\times10^{-16}1×10−16 and the Al+^++/Yb ratio at 1.6×10−171.6\times10^{-17}1.6×10−17 in fractional units compared to our previous measurements underscore the importance of repeated, high-precision comparisons by different laboratories. A key innovation in this work is the use of a common ultrastable reference delivered to all clocks via a 3.6 km phase-stabilized fiber link between two institutions. Derived from a cryogenic single-crystal silicon cavity, this reference improves comparison stability by a factor of 2 to 3 over previous systems, with an optical lattice clock ratio achieving a fractional instability of 1.3×10−161.3 \times 10^{-16}1.3×10−16 at 1 second. By enabling faster comparisons, this stability will improve sensitivity to non-white noise processes and other underlying limits of state-of-the-art optical frequency standards.
We report high-precision frequency ratio measurements between optical atomic clocks based on ^{27}Al^{+}, ^{171}Yb, and ^{87}Sr. With total fractional uncertainties at or below 3.2×10^{-18}, these measurements meet an important milestone criterion for redefinition of the second in the International System of Units. Discrepancies in ^{87}Sr ratios at approximately 1×10^{-16} and the Al^{+}/Yb ratio at 1.6×10^{-17} in fractional units compared to our previous measurements underscore the importance of repeated, high-precision comparisons by different laboratories. A key upgrade from our previous work is the use of a common ultrastable reference delivered to all clocks via a 3.6-km phase-stabilized fiber link between two institutions, enabling better accuracy and stability in frequency transfer. Derived from a cryogenic single-crystal silicon cavity, this reference improves comparison stability by a factor of 2-3 over previous systems, with an optical lattice clock ratio achieving a fractional instability of 1.3×10^{-16} at 1 s. Identifying individual clock stabilities with a three-corner-hat measurement, we demonstrate the most stable optical lattice and trapped-ion clocks used in a multispecies comparison. By enabling faster comparisons, this stability will improve sensitivity to nonwhite noise processes and other underlying limits of state-of-the-art optical frequency standards.
Optical atomic clocks that operate at frequencies up to 100,000 times higher than their microwave counterparts permit better resolutions and accuracies, while also providing more leeway in environmental control for out of lab applications. Many of the precision applications of these clocks, including relativistic geodesy and tests of fundamental physics rely on the intercomparison of at least two optical clocks. Relative comparisons that include single ion clocks, however, can require close to one month of continuous averaging to achieve measurement instabilities near 1 part in 1018. The long averaging times result from limits imposed on the quantum project noise as a result of signal detection from a single ion, as well as atom probe time limitations due to laser-atom decoherence. In this talk I will describe how the phase coherent properties of an optical frequency comb can be used to enable correlated and synchronous measurement of atomic clocks as a means to improve their relative measurement instability by close to a factor of 10, and nearly 100 times speed up in averaging time over conventional measurement techniques.
The optical atomic clocks have the potential to transform global timekeeping, relying on the state-of-the-art accuracy and stability, and greatly improve the measurement precision for a wide range of scientific and technological applications. Herein we report on the development of the optical clock based on 171Yb atoms confined in an optical lattice. A minimum width of 1.92-Hz Rabi spectra has been obtained with a new 578-nm clock interrogation laser. The in-loop fractional instability of the 171Yb clock reaches 9.1 × 10−18 after an averaging over a time of 2.0 × 104 s. By synchronous comparison between two clocks, we demonstrate that our 171Yb optical lattice clock achieves a fractional instability of 4.60 × 10 − 16 / τ .