Absolute frequency measurement of the In+ clock transition with a mode-locked laser

Area of Science:

• Atomic Physics
• Quantum Metrology
• Optical Clocks

Background:

• Accurate optical atomic clocks are crucial for fundamental physics tests and advanced technologies.
• Indium ions (In(+)) possess suitable properties for developing next-generation atomic clocks.
• Previous measurements of the In(+) clock transition lacked the required accuracy for metrological applications.

Purpose of the Study:

• To measure the absolute frequency of the In(+) 5s(2) (1)S(0)-5s5p (3)P(0) transition with unprecedented accuracy.
• To establish a new benchmark for optical frequency standards using a single trapped ion.
• To improve the accuracy of optical clock transitions by over two orders of magnitude.

Main Methods:

• Utilized a phase-coherent frequency chain to link the In(+) transition to a methane-stabilized HeNe laser.
• Employed a mode-locked femtosecond laser frequency comb to bridge a 37 THz frequency gap.
• Calibrated the HeNe laser against a primary atomic cesium fountain clock for absolute frequency determination.

Main Results:

• The absolute frequency of the In(+) clock transition at 237 nm was determined to be 1,267,402,452,899.92 (0.23) kHz.
• Achieved an accuracy of 1.8 parts in 10(13), limited by the HeNe laser reference uncertainty.
• This represents a significant improvement (>2 orders of magnitude) over previous measurements.

Conclusions:

• The measured In(+) transition frequency is the most accurate optical transition measurement in a single ion to date.
• This work provides a highly accurate frequency standard for potential use in future optical clocks.
• The results pave the way for enhanced precision in timekeeping and fundamental constant measurements.