¹⁷⁶Lu⁺ clock comparison at the 10^-18 level via correlation spectroscopy.

Area of Science:

• Atomic, Molecular, and Optical Physics
• Metrology and Measurement Science
• Quantum Information and Computation

Background:

• Optical atomic clocks achieve unprecedented precision, driving the redefinition of the second.
• Accuracies exceeding 1 part in 10¹⁸ are crucial for geodesy and fundamental physics tests.
• The ¹⁷⁶Lu⁺ ion's ¹S₀ to ³D₁ transition offers low sensitivity to external perturbations, ideal for high-accuracy clocks.

Purpose of the Study:

• To perform high-accuracy comparisons between two ¹⁷⁶Lu⁺ optical atomic clock references.
• To evaluate the performance of ¹⁷⁶Lu⁺ clocks for practical implementation at the 10⁻¹⁸ inaccuracy level.
• To determine the quadratic Zeeman coefficient for the ¹⁷⁶Lu⁺ reference transition.

Main Methods:

• Utilized correlation spectroscopy for high-accuracy comparisons between two independent ¹⁷⁶Lu⁺ atomic clocks.
• Conducted comparisons at varying magnetic fields to determine the quadratic Zeeman coefficient.
• Performed a low-field comparison to assess clock agreement at the 10⁻¹⁸ level.

Main Results:

• Determined the quadratic Zeeman coefficient for the ¹⁷⁶Lu⁺ reference frequency to be -4.89264(88) Hz/mT.
• Demonstrated agreement between two ¹⁷⁶Lu⁺ clocks at the 10⁻¹⁸ level, limited by averaging time.
• Achieved an evaluated uncertainty of 9 × 10⁻¹⁹ in the frequency difference, the lowest reported for independent optical references.

Conclusions:

• The ¹⁷⁶Lu⁺ ion is a highly promising system for optical atomic clocks operating at or below the 10⁻¹⁸ inaccuracy level.
• The demonstrated agreement validates the potential of ¹⁷⁶Lu⁺ clocks for next-generation metrology and fundamental science.
• This work sets a new benchmark for the precision of comparisons between independent optical atomic clock systems.