Electromagnetically Induced Transparency Spectra of Ladder Four-Level System with Quantum Frequency Mixing

TL;DR

This paper explores a generalized four-level quantum system demonstrating electromagnetically induced transparency and quantum frequency mixing, revealing new interference effects and enabling broad-band AC field sensing.

Contribution

It introduces a novel ladder-type four-level system with quantum frequency mixing, showing secondary Autler-Townes splitting and coexistence of multiple quantum interference effects.

Findings

Secondary Autler-Townes splitting observed in spectra

Continuous tunability of resonant frequency for broad-band sensing

Coexistence of Floquet channel interference and loop interference

Abstract

In this paper, we generalized the quantum frequency mixing technology to a ladder-type four-level system and studied its effect on electromagnetically induced transparency spectra. We found a secondary splitting of Autler-Townes splitting in the probing field transmission spectra, which could be understood by the effective Hamiltonian derived with multi-mode Floquet theory. The Frequency mixing scheme developed here enables continuous tunablity of the resonant frequency between upper levels, which facilitates the broad band sensing of AC field. Furthermore, by introducing an additional periodic driving, we realize an effective model that two distinct quantum interference effects coexist: interference among Floquet channels and loop interference arising from closed coherent pathways. Both interference effects could 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 with the total effective phase of the loop. This not only provides complementary readout for extracting the phase of AC field, but also establishes a new paradigm for coherent control in multi-level quantum systems.