Sr Lattice Clock at 1 x 10-16 Fractional Uncertainty by Remote Optical Evaluation with a Ca clock

Published

March 28, 2008

Author(s)

A D. Ludlow, T Zelevinsky, G K. Campbell, S Blatt, M M. Boyd, M de Miranda, M J. Martin, S M. Foreman, J Ye, Tara M. Fortier, Jason Stalnaker, Scott A. Diddams, Yann LeCoq, Zeb Barber, Nicola Poli, Nathan D. Lemke, K. Beck, Christopher W. Oates

Abstract

Optical atomic clocks promise timekeeping at the highest precision and accuracy, owing to their high operating frequency. The most accurate optical clocks are presently based on single trapped ions1, due to the exquisite control possible over their electronic and motional quantum states, as demonstrated in both clock and quantum information experiments. While neutral atoms enjoy high measurement precision from the use of large ensembles, a longstanding challenge for these systems is achieving control and measurement at similar uncertainties as for single trapped particles. Here we report an uncertainty evaluation of a Sr optical lattice clock at the 1x10^-16 fractional level, surpassing the best current evaluations of the Cs primary microwave standards. This demonstrates control of clock states for large ensembles of atoms approaching that of the best ion systems. Rigorous evaluation of high performance clocks is impossible without access to similarly performing clocks nearby. The work here is enabled by a remote (4 km) optical comparison between the Sr lattice clock at JILA and the Ca optical clock at NIST. This first high-performance optical clock comparison over km-scale urban distances demonstrates an important step for worldwide development of optical standards and is useful for testing fundamental physical laws and long baseline gravitational measurements. Blackbody-induced Sr clock shifts limit the present uncertainty, and we discuss means to overcome this problem affecting many developing standards. Intriguingly, we report density-dependent frequency shifts in spin-polarized, ultracold, fermionic Sr and we find these shifts can be reduced. Precise understanding of interactions among many lattice-confined atoms will allow clean preparation, control, and readout of atoms for quantum simulations. Our measurements with thousands of atoms approach the fundamental quantum noise limit, opening the possibility of spin squeezing in optical lattices to combine precision measurement and quantum optics.

Citation

Science

Volume

319

Pub Type

Journals

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Keywords

atomic clocks, optical frequency standards, remote frequency comparisons

Citation

Ludlow, A. , Zelevinsky, T. , Campbell, G. , Blatt, S. , Boyd, M. , de, M. , Martin, M. , Foreman, S. , Ye, J. , Fortier, T. , Stalnaker, J. , Diddams, S. , LeCoq, Y. , Barber, Z. , Poli, N. , Lemke, N. , Beck, K. and Oates, C. (2008), Sr Lattice Clock at 1 x 10^-16 Fractional Uncertainty by Remote Optical Evaluation with a Ca clock, Science, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=50639 (Accessed October 12, 2025)