Electromagnetically-induced-transparency spectra of a ladder-type four-level system with quantum frequency mixing
Phys. Rev. A 114, 012805 – Published 8 July, 2026
DOI: https://doi.org/10.1103/8qj4-1h31
Abstract
In this paper, we extend the quantum-frequency-mixing technology to a ladder-type four-level system and study its effect on electromagnetically-induced-transparency spectra. We find a secondary splitting of Autler-Townes splitting in the probing field transmission spectra, which can be understood by the effective Hamiltonian derived with multimode Floquet theory. The frequency-mixing scheme developed here enables continuous tunability of the resonant frequency between upper levels, which facilitates the broadband sensing of the ac field. Furthermore, by introducing additional periodic driving, we realize an effective model in which two distinct quantum interference effects coexist: interference among Floquet channels and loop interference arising from closed coherent pathways. Both interference effects can be read out from the transmission spectra independently. The changing of the distance between double-splitting peaks represents the interference of Floquet channels, while their asymmetric linewidth broadening is linked to the total effective phase of the loop. This not only provides a complementary readout for extracting the phase of the ac field but also establishes a paradigm for coherent control in multilevel quantum systems.
