Liquid-Nitrogen-Cooled ​^{40}Ca^{+} Ion Optical Clock with a Systematic Uncertainty of 4.4×10^{-19}.

Area of Science:

• Atomic Physics
• Quantum Metrology
• Optical Clocks

Background:

• Optical atomic clocks are crucial for fundamental physics and metrology.
• Trapped-ion optical clocks face challenges from environmental noise and systematic uncertainties.

Purpose of the Study:

• To develop a high-precision single-ion optical clock based on the ^{40}Ca^{+} ion.
• To minimize systematic uncertainties, particularly those from blackbody radiation and Doppler shifts.
• To investigate the benefits of a cryogenic environment for trapped-ion clocks.

Main Methods:

• Utilized the 4S_{1/2}→3D_{5/2} transition of the ^{40}Ca^{+} ion.
• Operated the clock in a liquid nitrogen cryogenic environment.
• Implemented a refined temperature evaluation and 3D sideband cooling techniques.
• Precisely determined the average Zeeman coefficient.

Main Results:

• Achieved a total systematic uncertainty of 4.4×10^{-19}.
• Reduced frequency uncertainty from blackbody radiation and second-order Doppler shift.
• Significantly reduced quadratic Zeeman shift uncertainty with a determined Zeeman coefficient of 14.345(15) Hz/mT².
• Observed the lowest reported heating rate in trapped-ion optical clocks due to ambient electric field noise.

Conclusions:

• The ^{40}Ca^{+} ion optical clock in a cryogenic environment demonstrates exceptional precision.
• Cryogenic operation and advanced cooling significantly mitigate systematic errors.
• This work sets a new benchmark for trapped-ion optical clock performance.