A clock network for geodesy and fundamental science.

Area of Science:

• Atomic Physics
• Metrology
• Geophysics
• Astronomy
• Fundamental Physics

Background:

• Optical clocks offer unparalleled precision for scientific applications.
• Comparing distant optical clocks is crucial for advancing geo-science, astronomy, and fundamental physics.
• Existing methods for long-distance clock comparison face limitations in precision and speed.

Purpose of the Study:

• To establish a phase-coherent frequency link for comparing distant optical clocks.
• To demonstrate the capability of high-resolution, long-distance optical clock comparisons.
• To assess the potential for redefining the SI second using advanced clock comparison techniques.

Main Methods:

• Utilized two strontium lattice optical clocks.
• Established a 1,415 km phase-coherent frequency transfer link via telecom fiber between Paris and Braunschweig.
• Measured clock comparison uncertainty and precision over the established link.

Main Results:

• Achieved agreement between two strontium optical clocks with an uncertainty of 5 × 10(-17).
• Demonstrated a fractional precision of 3 × 10(-17) after 1,000 seconds of averaging.
• The optical frequency transfer contributed negligibly to the overall comparison uncertainty, limited primarily by the clocks themselves.
• Exceeded previous long-distance clock comparison performance by an order of magnitude in precision and four orders of magnitude in speed.

Conclusions:

• The developed optical frequency transfer method enables high-resolution international clock comparisons.
• This technology paves the way for a potential redefinition of the SI second.
• Facilitates all-optical dissemination of the SI second, enhancing global timekeeping standards.