Actualization as Physical Mechanism: Implications of Relational Actualism for Quantum Computing and Quantum Thermodynamics

Relational Actualism (RA) proposes that the transition from quantum potentia to classical actuality is grounded in a precise physical criterion: an irreversible increase in quantum relative entropy Δ S (ρ‖σ₀) > 0 with respect to the vacuum. In the perturbative regime this coincides with the on-shell condition p^μ p_μ = m²c², at which a mediating boson crosses the kinematic threshold from virtual to real and an irreversible vertex is inscribed into the growing causal DAG. This paper develops the implications for quantum computing and quantum thermodynamics. For quantum computing, the Kinematic Snap provides a principled physical floor on decoherence and yields the Kinematic Coherence Bound: the maximum fault-tolerant array size is N_ = η · pₜh, where η is the single-qubit quality factor and pₜh is the fault-tolerance threshold. This is a structural constraint not anticipated by standard quantum error correction theory: logical error rates grow with N because each added qubit is an additional kinematic site at which actualization can occur. For quantum thermodynamics, RA grounds Landauer's principle in the causal DAG structure, resolves Maxwell's demon without information-theoretic postulates, gives the fluctuation theorems a precise actualization-event interpretation, and establishes that the thermodynamic arrow of time is structural rather than emergent. A key technical result: the quantum relative entropy is frame-independent by a machine-verified Lean 4 theorem (frameᵢndependence in RAAQFTProofsᵥ10. lean), proved using the continuous functional calculus unitary-conjugation lemma of the Lean-QuantumInfo library. The fault-tolerance threshold, the speed of light c = lP/tP, and the biological Causal Firewall are all the same Erdős-Rényi percolation transition at different scales of the causal graph.