171 Yb optical lattice clock with uncertainty below 5×10 −18

Abstract We report improved performance of the 171 Yb optical lattice clocks at East China Normal University, achieving a total uncertainty of 4.4×10 −18 for the Yb2 clock through high-precision synchronous frequency comparisons with the similar Yb1 clock. A 578 nm laser for the 1 S 0 – 3 P 0 clock transition is cavity-stabilized using a newly developed ultra-stable laser system, featuring a reduced thermal-noise limit compared to its predecessor. Through systematic optimization, including suppression of technical noise in the laser system and detailed evaluation of frequency shifts, such as collision, blackbody radiation, lattice, and Zeeman shifts, we achieved stable clock-transition spectra for the m F = ± 1/2 spin states using 400 ms interrogation pulses, obtaining a Fourier-limited linewidth of 2 Hz. Based on these optimizations, synchronous comparisons between two 171 Yb clocks enable a fractional frequency instability for each clock to average at a rate of 2.0×10 −16 / τ , reaching 1.9 − 0.4 + 1.2 ×10 −18 at 8000 s, which provides the resolution necessary for high-precision systematic evaluation. Furthermore, a complementary asynchronous comparison accounting for the Dick noise yields an instability of 4.0×10 −18 at 8000 s. The combination of these high-precision comparisons and rigorous frequency shift evaluations validates the total systematic uncertainty below 5×10 −18 .