Absolute frequency measurement of the 40Ca+ 4s(2)S_(1/2)-3d(2)D_(5/2) clock transition

Area of Science:

• Atomic Physics
• Quantum Metrology

Background:

• Accurate atomic clocks are crucial for fundamental physics tests and technological applications.
• Calcium ion (Ca+) clocks offer potential advantages over current standards like Cesium (Cs).

Purpose of the Study:

• To perform the first absolute frequency measurement of the 40Ca+ 4s 2S1/2–3d 2D5/2 electric-quadrupole transition.
• To achieve a measurement uncertainty approaching the level of the Cs atomic standard.

Main Methods:

• Utilized a single, laser-cooled 40Ca+ ion confined in a linear Paul trap.
• Employed a frequency comb referenced to a transportable Cesium atomic fountain clock for high-precision frequency measurement.
• Carefully corrected for various systematic frequency shifts.

Main Results:

• Determined the absolute clock transition frequency of 40Ca+ to be 411 042 129 776 393.2(1.0) Hz.
• Achieved a fractional uncertainty within a factor of 3 of the Cs atomic standard.
• Measured the Landé g factor of the 3d 2D5/2 level as 1.200 334 0(3).

Conclusions:

• This work establishes a new high-precision frequency standard for the 40Ca+ ion.
• The achieved accuracy demonstrates the potential of Ca+ ions for next-generation atomic clocks.
• Provides crucial data for advancing atomic physics and metrology.