Novel nonlinear processes, higher-order molecular coupling and multiphoton interactions : a quantum electrodynamical formulation

Kan-ichi Yokoyama

Kochise Bennett, Vladimir Chernyak, Shaul Mukamel

The nonlinear optical response of a system of molecules often contains contributions whereby the products of lower-order processes in two separate molecules give signals that appear on top of a genuine direct higher-order process with a single molecule. These many-body contributions are known as cascading and complicate the interpretation of multidimensional stimulated Raman and other nonlinear signals. In a quantum electrodynamic treatment, these cascading processes arise from second-order expansion in the molecular coupling to vacuum modes of the radiation field, i.e., single-photon exchange between molecules, which also gives rise to other collective effects. We predict the relative phase of the direct and cascading nonlinear signals and its dependence on the microscopic dynamics as well as the sample geometry. This phase may be used to identify experimental conditions for distinguishing the direct and cascading signals by their phase. Higher-order cascading processes involving the exchange of several photons between more than two molecules are discussed.

Farhad H. M. Faisal, A. Dalgarno

Guang S. He

Abstract Laser Stimulated Scattering and Multiphoton Excitation is the first book that comprehensively covers the following three major areas: (1) Quantum electrodynamic theory of stimulated scattering and multiphoton excitation processes; (2) Various stimulated scattering effects, including the early discovered stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS), the later investigated stimulated Kerr scattering (SKS), and the recently developed stimulated Rayleigh–Bragg scattering (SRBS) and stimulated Mie scattering (SMS); (3) Multiphoton excitation-based nonlinear optical effects, photoelectric effects, atomic and molecular ionization effects, and molecular dissociation effects. Each chapter covers: (i) the concept and mechanism description, (ii) the necessary theoretical formulation, (iii) the experimental research achievements, and (iv) the scientific/technological applications. Laser Stimulated Scattering and Multiphoton Excitation is useful and suitable for academics, experts, and students working or interested in the areas of nonlinear optics, nonlinear photonics, laser spectroscopy, physical optics, physical chemistry, and optoelectronic engineering.

Farhad H. M. Faisal

Yun Chen, Geng Zhao, Huanhuan Wei +5 more

Microwave shielding has recently emerged as a powerful tool for engineering interactions in ultracold polar molecules, yet its potential for controlling cavity quantum electrodynamics remains largely unexplored. Here, we investigate a molecular cavity quantum electrodynamics platform in which two microwave-shielded polar molecules are coupled to a single optical cavity mode and demonstrate that shielding-induced interactions provide a unified mechanism for both photon blockade and Bell-state protection. The anisotropic interaction reshapes the few-excitation spectrum by enhancing its anharmonicity, thereby suppressing multiphoton transitions and improving the single-photon purity by more than three orders of magnitude. The enhanced blockade is accompanied by the emergence of negative longitudinal spin correlations, revealing the interaction-induced suppression of simultaneous molecular excitations. We further show that the photon statistics are highly sensitive to the relative molecular configuration, with positional variations on the scale of the relative zero-point fluctuation substantially modifying the blockade performance. Beyond few-photon nonlinear optics, the same interaction protects an initially prepared molecular Bell state by dispersively decoupling molecular excitations from the lossy cavity mode, thereby suppressing cavity-mediated dissipation and slowing the fidelity decay. Our results establish microwave-shielded interactions as a unified interaction resource for engineering few-photon nonlinearities and protecting quantum states in molecular cavity-QED systems.