Thermal Decoherence and Population Transfer of MeV Channeling Electrons in Diamond

arXiv:2602.16529v2 Announce Type: replace-cross Abstract: Channeling radiation from MeV-regime electrons is governed by transitions between quantized transverse bound states, but experimental spectra are strongly modified by thermal diffuse scattering. To capture these open-system dynamics, a frozen-phonon multislice framework is combined with bound-state projection analysis to construct depth-dependent reduced density matrices in selected transverse manifolds. Beyond reproducing experimental channeling-radiation transition energies, this approach separates thermal population transfer, intra-manifold decoherence, and cross-manifold coherence loss. Applied to 16.9 MeV axial electron channeling in $\langle100\rangle$ diamond, the results show approximately exponential population decay from the initially occupied states, accompanied by strongly channel-dependent feeding among low-lying manifolds. Starting from a coherent superposition within the degenerate 2p manifold, stochastic symmetry breaking by thermal displacements drives the intra-manifold purity toward the maximally mixed limit, indicating rapid phase scrambling. Under 1s initialization, population transferred into the 2p and 3d manifolds remains internally close to maximally mixed, yet a weak residual 2p-3d cross-manifold coherence persists. This framework goes beyond static mean-field thermal broadening and provides a microscopic basis for evaluating population dynamics and coherence lifetimes in strongly quantized channeling-radiation systems.