Three-photon coherent spectroscopy of Rydberg states of 87Rb atoms with 778 nm and 1260 nm laser scheme in Rb atoms

Rydberg atoms, with their high electrical polarizability and strong transition dipole moments, are highly sensitive to subtle changes in external electric fields, making them ideal for quantifying the intensity of microwaves and related electric fields. Recently, research on electric field sensing using Rydberg atoms has been actively conducted. To improve sensitivity, a new scheme utilizing three lasers (780 nm, 776 nm, and 1260 nm) has been introduced, replacing the conventional approach of generating the Rydberg state with two lasers (780 nm and 480 nm). This three-laser setup allows for narrower linewidths in Three-Photon EIT and EIA signals, enabling the electric field strength to be measured with higher sensitivity.

However, the three-laser system involves complexities in laser frequency stabilization using an ultra-low expansion (ULE) cavity and significant constraints on miniaturization. To address these issues, we developed a method that uses only two lasers (778 nm and 1260 nm) while implementing the same energy structure as the three-laser system. By utilizing the 5S1/2–5D5/2–55F7/2 transition scheme of the Rb Rydberg atom, we successfully observed Rydberg spectroscopic signals under this setup. These research results will contribute to the advancement of low-noise, high-sensitivity RF electric field quantum sensors.