Magic-Angle Photonic Quantum Computing: Geometric Decoherence Protection, the Trisection Qutrit, and Falsifiable Predictions from a (3+3) Spacetime Framework

We apply the (3+3) spacetime framework 1, 6 — a six-dimensional Einstein–Aether construction with three spatial and three temporal dimensions, the third time dimension compactified as a discrete two-sphere S² with Ncells = 2¹⁵² Planck-area cells — to photonic quantum computing. The framework identifies the photon as a null arc (a c-vector configuration with vT = vₜ₂ = vₜ₃ = 0 and vₛpatial = c) corresponding to the n = 0 Kaluza–Klein zero-mode on S². From this single identification three Level-1 structural results follow: (i) the photon's polarization Poincaré sphere is geometrically the third time dimension's S²; single-qubit gates are physical S² rotations and the Born rule is Malus's law as S² projection; (ii) photons inherit no t₃-winding decoherence channels, with cosmological coherence floor τcosm = 1/H₀ ≈ 14. 5 Gyr §14bis. 46. 4 of 6 and practical decoherence by photon loss as t₃ entrainment; (iii) the cross-Kerr nonlinearity scales as χ⁽³⁾ ∼ α² = 5. 3 × 10⁻⁵ from two successive c-vector rotations each of amplitude √α. We give a self-contained derivation in §5. 4 of the χ⁽³⁾ ∼ α² scaling from the Lagrangian-level photon-photon-via-radion vertex L = − (g₀/4) Φ² F⏛⏜ F^μν|ₙode with bare coupling g₀ = (4/9) εZPE², through radion integration-out at optical frequencies, to the four-loop running g₀ → α (drawing on §16–§17 of 6). Sections 5. 5–5. 9 establish the structural form of the nodal-cone TPA-suppression factor ηₙode: the breathing-mode contribution at the cone vanishes geometrically because the Y₂, ₀ (ϑₙode) = 0 identity that defines the cone latitude also eliminates the breathing's metric perturbation there (§5. 7) ; the higher-multipole tail is bounded at ηₙode|ₕigher ≲ 10⁻⁵ using the framework's identified spectrum from 6 (§5. 8) ; and the same Z₃ symmetry that organises SU (3), three-generation fermion structure, and tribimaximal PMNS mixing also protects the qutrit basis at the trisection vertices (§5. 9). Combining these structural results with anchored medium-specific estimates for silicon-on-insulator (Kₘedium ≈ 0. 10–0. 20), silicon nitride (0. 03–0. 08, lowest), and thin-film lithium niobate (0. 05–0. 15) (Appendix B), the framework predicts ηₙode ≈ Kₘedium ≈ 0. 03–0. 20 across candidate platforms — silicon nitride is identified as the optimal platform — dominated entirely by medium contributions rather than framework-vacuum dynamics, and decisively testable by the §6. 7 thermal MZI experiment (2027–2030). The magic-angle latitude ϑₙode = arccos (1/√3) = 54. 74° is the same magic angle as in NMR magic-angle spinning, and the underlying physics (averaging-out of Y₂, ₀ dipolar interactions) is structurally identical. Six engineering proposals leverage these results: null-arc qubit encoding; the nodal-cone LOQC architecture (qubits at the magic-angle latitude where Y₂, ₀ vanishes and the leading TPA channel is suppressed) ; (3+3) measurement protocols with t₃-entrainment-strength control; trisection qutrit photonic computing (log₂ 3 ≈ 1. 585 bits per photon, with Z₃-symmetric coherence protection giving ηqutrit ≈ 0. 06–0. 21 comparable to qubit ηₙode — a 58. 5% information-density gain at essentially no extra coherence cost) ; boson sampling reframed as null-arc network interference; and a nodal-cone photonic-crystal integrated chip. Three testable predictions are organised into a year-resolved 2026–2030+ falsifiability timeline (§6. 7). All claims are explicitly tagged Level 1 (geometric, derived), Level 2 (anchored prefactor), or Level 3 (engineering speculation) ; the room-temperature fault-tolerance projection of §9 is an explicit Level-3 conditional argument with dependency chain made explicit. A self-contained framework digest is given in §1. 7; readers unfamiliar with the (3+3) programme can read §1. 7 alone to decide whether to continue.