Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Nature Physics

Improved interspecies optical clock comparisons through differential spectroscopy

May E. Kim, William F. McGrew, Nicholas V. Nardelli, Ethan Clements, Youssef S. Hassan, Xiaogang Zhang, Jose L. Valencia, Holly Leopardi, David B. Hume, Tara M. Fortier, Andrew D. Ludlow, David R. Leibrandt

Published Nov 28, 2022• 39 citations
Publisher
DOI
10.1038/s41567-022-01794-7

Related papers

Differential clock comparisons with a multiplexed optical lattice clock

Xin Zheng, Jonathan Dolde, Varun Lochab +3 more

Nature•Feb 16, 2022•149 citations

Optical atomic clock comparisons using correlation spectroscopy (Conference Presentation)

May E. Kim

Optical and Quantum Sensing and Precision Metrology II•Mar 27, 2020•0 citations

Optical coherence between atomic species at the second scale: improved clock comparisons via differential spectroscopy

May E. Kim, William F. McGrew, Nicholas V. Nardelli +9 more

Comparisons of high-accuracy optical atomic clocks \cite{Ludlow2015} are essential for precision tests of fundamental physics \cite{Safronova2018}, relativistic geodesy \cite{McGrew2018, Grotti2018, Delva2019}, and the anticipated redefinition of the SI second \cite{Riehle2018}. 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 \cite{Hume2016}, a comparison protocol that enables interrogating beyond the OLO coherence time. By phase-coherently linking a zero-dead-time (ZDT) \cite{Schioppo2017} 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 \cite{network2020frequency} of nearly an order of magnitude. To our knowledge, this result represents the most stable interspecies clock comparison to date.

arXiv:2109.09540•Sep 20, 2021•3 citations

Improving Optical Clocks

Science•Nov 18, 2004•0 citations

Differential Spectroscopy of Atomic Clocks for Improved Measurement Instability

Nicholas V. Nardelli, Xiaogang Zhang, Ethan Clements +8 more

Using frequency comb mediated phase-coherent and synchronous clock comparisons we demonstrate close to a factor of 10 improvement in short-term measurement instability, σy(τ) < 2 x 10-16 @ 1s averaging, between 171Yb and 27Al+ optical clocks.

Conference on Lasers and Electro-Optics•Jan 1, 2021•2 citations

Interspecies clock comparison below $5 \times 10^{-18}$ uncertainty with a transportable clock

Chetan Vishwakarma, Ingo Nosske, Tim Lücke +6 more

We report a measurement of the optical frequency ratio between the $^2\mathrm{S}_{1/2}(F=0)$--${^2\mathrm{F}_{7/2}(F=3)}$ electric-octupole (E3) transition of $^{171}$Yb$^{+}$ and the $^1\mathrm{S}_0$--${^3\mathrm{P}_0}$ transition of $^{87}$Sr, $ν_{\mathrm{Yb}^{+}}/ν_\mathrm{Sr} = 1.495\,991\,618\,544\,900\,588\,1(65)$. Reaching a fractional uncertainty of $4.3 \times 10^{-18}$, this result improves upon the previous best by more than a factor of three and is among the few that meet the requirements for interspecies clock comparisons specified by the roadmap towards the redefinition of the SI second. The comparison is between a transportable optical lattice clock and a stationary single-ion clock. It spans a period of nearly two years, during which the transportable clock was intermittently operated off-campus. The ratio was reproducibly measured during four separate campaigns, which are consistent within their statistical uncertainties. The results demonstrate reproducible $10^{-18}$ level operation of the transportable clock and thus validate its application for chronometric geodesy and as a transfer standard for inter-institute clock comparisons, e.g., in the absence of optical fiber links.

physics.atom-phCross-listedarXiv:2608.01916•Aug 4, 2026
Comparisons of high-accuracy optical atomic clocks \cite{Ludlow2015} are essential for precision tests of fundamental physics \cite{Safronova2018}, relativistic geodesy \cite{McGrew2018, Grotti2018, Delva2019}, and the anticipated redefinition of the SI second \cite{Riehle2018}. 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 \cite{Hume2016}, a comparison protocol that enables interrogating beyond the OLO coherence time. By phase-coherently linking a zero-dead-time (ZDT) \cite{Schioppo2017} 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 \cite{network2020frequency} of nearly an order of magnitude. To our knowledge, this result represents the most stable interspecies clock comparison to date.
Interspecies clock comparison below 5×10−185 \times 10^{-18}5×10−18 uncertainty with a transportable clock
We report a measurement of the optical frequency ratio between the 2S1/2(F=0)^2\mathrm{S}_{1/2}(F=0)2S1/2​(F=0)--2F7/2(F=3){^2\mathrm{F}_{7/2}(F=3)}2F7/2​(F=3) electric-octupole (E3) transition of 171^{171}171Yb+^{+}+ and the 1S0^1\mathrm{S}_01S0​--3P0{^3\mathrm{P}_0}3P0​ transition of 87^{87}87Sr, νYb+/νSr=1.495 991 618 544 900 588 1(65)ν_{\mathrm{Yb}^{+}}/ν_\mathrm{Sr} = 1.495\,991\,618\,544\,900\,588\,1(65)νYb+​/νSr​=1.4959916185449005881(65). Reaching a fractional uncertainty of 4.3×10−184.3 \times 10^{-18}4.3×10−18, this result improves upon the previous best by more than a factor of three and is among the few that meet the requirements for interspecies clock comparisons specified by the roadmap towards the redefinition of the SI second. The comparison is between a transportable optical lattice clock and a stationary single-ion clock. It spans a period of nearly two years, during which the transportable clock was intermittently operated off-campus. The ratio was reproducibly measured during four separate campaigns, which are consistent within their statistical uncertainties. The results demonstrate reproducible 10−1810^{-18}10−18 level operation of the transportable clock and thus validate its application for chronometric geodesy and as a transfer standard for inter-institute clock comparisons, e.g., in the absence of optical fiber links.