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Towards the optical second: verifying optical clocks at the SI limit.

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Researchers precisely measured the Ytterbium-171 optical atomic transition frequency, achieving the most accurate measurement to date. This work is a key step towards redefining the SI second using optical clocks and provides new insights into fundamental physics constants.

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Area of Science:

  • Metrology and Timekeeping
  • Atomic Physics
  • Fundamental Constants

Background:

  • The current definition of the second is based on a microwave atomic transition in Cesium-133.
  • Redefining the second using optical atomic transitions promises significantly higher precision.
  • Ensuring continuity with the current definition requires precise measurement of optical clock frequencies relative to Cesium standards.

Purpose of the Study:

  • To measure the absolute frequency of the 1S0 → 3P0 transition in 171Yb.
  • To compare optical clock frequencies with international primary and secondary frequency standards.
  • To test fundamental physics by constraining variations in the electron-to-proton mass ratio and its coupling to gravity.

Main Methods:

  • Utilized satellite time and frequency transfer to link the 171Yb optical clock to Cesium standards.
  • Performed 79 measurement runs over eight months to establish the absolute frequency.
  • Analyzed long-term frequency data to derive constraints on fundamental constant variations.

Main Results:

  • The absolute frequency of the 171Yb transition was measured to be 518 295 836 590 863.71(11) Hz with a fractional uncertainty of 2.1 × 10-16.
  • The Cs-Yb-Sr-Cs frequency measurement loop was closed with an uncertainty below 3 × 10-16, limited by the current SI second realization.
  • New bounds were inferred for the electron-to-proton mass ratio's variation with gravitational potential and time.

Conclusions:

  • This work represents a significant advancement towards an optical definition of the SI second.
  • The achieved accuracy pushes the limits of the current SI second realization.
  • The results provide stringent constraints on variations of fundamental constants, impacting tests of general relativity and cosmology.