Journal of Physics B Atomic Molecular and Optical Physics
Non-Markovian effects in optical Bloch dynamics: geometry and power spectra
Octavian Postavaru
Abstract
Abstract Fractional-order extensions of quantum dynamical equations provide an effective framework for incorporating memory and non-Markovian effects into the description of open quantum systems. In this work we investigate a laser-driven two-level system governed by a fractional generalization of the optical Bloch equations based on Caputo derivatives. The resulting evolution is analyzed in phase space, where temporal memory manifests itself through systematic geometric modifications of the relaxation trajectories. In particular, decreasing the fractional order produces a rotation and contraction of the phase-space spirals, together with a displacement of their effective centers, revealing a consistent reorganization of the dissipative oscillatory dynamics. We further connect this time-domain behavior to experimentally accessible frequency-domain signatures by constructing the incoherent resonance-fluorescence power spectrum from the stationary dipole correlation function. The fractional spectra recover the classical three-peak (Mollow-type) structure in the limit α → 1 , while for α < 1 they exhibit a redistribution of spectral weight accompanied by modified peak localization, sideband separation, and intensity ratios. These results demonstrate how fractional dynamics links the geometry of relaxation to measurable spectral morphology in non-Markovian quantum systems.