Quantum Multiphoton Rabi Oscillations in Waveguide QED

Chip-scale nanophotonics, with waveguide QED as a crucial component, remains instrumental in advancing the field of quantum information processing and communication. A key facet of photonic technologies revolves around the scattering of coherent light across a two-level system which leads to Rabi oscillations in the semiclassical, strong-field limit. We analytically investigate the scattering dynamics of multiphoton Fock states as they encounter a two-level emitter and examine both the weak-field and strong-field regimes that exhibit widely disparate dynamical features. The excitation amplitude of the qubit features a linear superposition of various independent scattering events originating from the possibility of sequential photon absorptions and emissions. In the strong pumping limit characterized by asymptotically large photon numbers, all scattering amplitudes attain comparable significance, and signatures of Rabi-like oscillatory dynamics are recovered, closely mirroring semiclassical predictions. Hence, our formulation affords a robust theoretical foundation for understanding the transition from finite to asymptotically large photon numbers. We also explore the scattering dynamics of pulsed wave packets, unveiling strongly enhanced excitation efficiency even in scenarios involving a few photons. This has practical implications for quantum computing protocols based on multiphoton states of light and for waveguide-integrated photonic technologies.