Hyperbolicity and Well-Posedness of the Gay-Balmaz–Tronci Hybrid Quantum–Classical Closure

This manuscript establishes the first rigorous well-posedness theory for the exact-factorization hybrid quantum–classical closure of Gay-Balmaz and Tronci. The central result, the Covariance-Symplectic Obstruction Theorem, shows the uniformly hyperbolic admissible sector is generically empty, with local well-posedness instead established on a weaker "uniformly symmetrizable" sector via an explicit microlocal symmetrizer and a Friedrichs–Kato existence argument. A companion Rank-Deficiency Theorem classifies six standard device Hamiltonians (transmon-resonator, tunable coupler, Rydberg array, trapped-ion, optomechanical, and Kerr-cat architectures) as excluded from the hyperbolic sector, connecting the abstract theory to concrete qubit platforms.