Quantum coherent-state model delivers first closed-form inverse Compton spectrum without simulation

The framework replaces multiparticle classical or semiclassical tracking with a direct QED calculation. For a Gaussian laser pulse the scattered spectrum emerges from the overlap of the electron momentum distribution with the photon field operators, recovering the Landau-Lifshitz equation exactly in the classical limit. Validation against published inverse-Compton data shows spectral shapes match within experimental uncertainty while eliminating the statistical noise inherent in Monte-Carlo codes.

Existing models either demand large-scale particle-in-cell runs or invoke unquantified approximations for the laser envelope. Rogers identifies that both families share a structural limitation: they cannot propagate the full quantum state of the field through the interaction without truncation. The coherent-state approach removes that truncation for the Gaussian case, exposing how phase-space diffusion previously attributed to quantum stochasticity is already captured by the classical radiation-reaction term.

The method is currently restricted to Gaussian pulses and unpolarized electrons. Extension to arbitrary temporal profiles or spin-polarized beams will require numerical quadrature of the same overlap integrals rather than new simulations. If the analytic structure generalizes, compact ICS sources could move from empirical tuning to first-principles spectrum prediction within five years.