Interference between four-wave and six-wave mixing signals is observed in a four-level atomic system due to atomic coherence. The experimental and theoretical conditions for generating such interesting effects are investigated.
We investigate the interplay between six-wave mixing (SWM) and four-wave mixing (FWM) resulting from atomic coherence and polarization beat in a four-level atomic system. The dressed FWM evolution and competition pathways can be controlled by the coupling field to exhibit two FWM and SWM turning points, FWM+SWM, and FWM+FWM interference regions. Quantum interference between two FWM or one FWM and one SWM channels leads to nonlinear signal enhancement and suppression under different conditions. The fifth-order nonlinear response can be obtained by the phase control of the polarization beat between the FWM and SWM signals.
We present new results on the coherent control of a four-wave mixing signal in rubidium vapor involving Rydberg levels. By varying the relative polarizations of the laser beams responsible for the nonlinear process, we control atomic excitation routes and thus quantum interference in the medium. We observed interference fringes as a function of the relative polarizations and further developed a theoretical model based on the density-matrix formalism that is in very good agreement with our experimental results.