An  ⁸⁸Sr⁺ optical frequency standard for the NIST timescale

We present the current status of our singly-trapped ⁸⁸Sr⁺ ion based clock. While the S_1/2 -> D_5/2 transition in Sr⁺ can support an uncertainty competitive with the best candidate standards [1-3], we target a comparatively modest uncertainty of <10^-16. Our primary objective is high operational uptime so the clock can meaningfully discipline the atomic clock timescale generating UTC(NIST). The strontium ion is an excellent candidate for a robust frequency standard as lasers at the necessary wavelengths (within 400-1200 nm) are all mature technologies. We minimize frequency shifts due to micromotion by operating at the “magic” RF trapping frequency where the relativistic doppler shift and scalar Stark shift cancel. Laser beams for ion creation, state control, and detection are delivered with only two beamlines. In the multi-wavelength beamline, the photoionization, cooling, repump, state preparation and clear-out laser beams are directed from a single photonic crystal fiber to the ion. The intensity-stabilized spectroscopy beam is counter-propagating to the first beamline. Comparison with the NIST-F4 cesium fountain enables absolute frequency measurements of the optical transition.

 

[1] C. Marceau et al.  Metrologia 62 045001 (2025)

[2] T. Lindvall et al. Phys. Rev. Applied 24 044082 (2025)

[3] M. Steinel et al. Phys. Rev. Lett. 131 083002 (2023)

[4] A Madej, APS DAMOP 2013 T7-001 (2013).