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Improved interspecies optical clock comparisons through differential spectroscopy



May E. Kim, Will McGrew, Nicholas Nardelli, Ethan Clements, Youssef Hassan, Xiaogang Zhang, Jose Valencia, Holly Leopardi, David Hume, Tara Fortier, Andrew Ludlow, David Leibrandt


Comparisons of high-accuracy optical atomic clocks \citeLudlow2015} are essential for precision tests of fundamental physics \citeSafronova2018}, relativistic geodesy \citeMcGrew2018, Grotti2018, Delva2019}, and the anticipated redefinition of the SI second \citeRiehle2018}. The scientific reach of these applications is restricted by the statistical precision of interspecies comparison measurements. The instability of individual clocks is limited by the finite coherence time of the optical local oscillator (OLO), which bounds the maximum atomic interrogation time. In this letter, we experimentally demonstrate differential spectroscopy \citeHume2016}, a comparison protocol that enables interrogating beyond the OLO coherence time. By phase coherently linking a zero-dead-time (ZDT) \citeSchioppo2017} \Yb optical lattice clock with an \Al single-ion clock via an optical frequency comb and performing synchronised Ramsey spectroscopy, we show an improvement in comparison instability relative to our previous result \citenetwork2020frequency} of nearly an order of magnitude. To our knowledge, this result represents the most stable interspecies clock comparison to date.
Nature Physics


Kim, M. , McGrew, W. , Nardelli, N. , Clements, E. , Hassan, Y. , Zhang, X. , Valencia, J. , Leopardi, H. , Hume, D. , Fortier, T. , Ludlow, A. and Leibrandt, D. (2022), Improved interspecies optical clock comparisons through differential spectroscopy, Nature Physics, [online], (Accessed July 21, 2024)


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Created November 28, 2022, Updated May 1, 2023