Phase-Resolved Spatial-Harmonic Experiment: Protocol for Testing a Coherence-Gradient Transport Term in Warm Rubidium Vapor

A prospective, pre-registered-style acquisition protocol for testing whether warm rubidium vapor exhibits an additional normalized-coherence-gradient transport contribution, dψ/dt = D ∂xx ψ + β (∂x Cσ[ψ])(∂x ψ), beyond independently calibrated conventional models. The protocol specifies phase-resolved (complex-field) measurement of second and third spatial harmonics, rival-model comparison (heat diffusion, intensity-dependent diffusion, Kerr/reaction response, variance-gradient transport, instrumental nonlinearity), blind holdout prediction, and planning targets for detection. This is a proposal only: no experiment has been performed and no observations are reported. A positive result would not by itself identify a unique causal mechanism. Prepared with assistance from Claude (Anthropic).