Non-Blocking Photonic Entanglement Routing and Physical-Layer Deterministic Interlocks for Distributed Quantum Data Centers: Scaling Willow-Class Modular Cryostats via the PHOENIX_BRIDGE Fabric

Scaling fault-tolerant quantum computing (FTQC) beyond monolithic dilution cryostats demands distributed architectures connecting hundreds of discrete QPUs across a quantum data center fabric. While point-to-point electro-optic links such as PHOENIX_BRIDGE resolve the single-vessel cryogenic cooling bottleneck (15 mK thermal saturation), multi-cryostat clustering faces a severe networking dilemma: conventional quantum repeater architectures rely on matter-based quantum memories that introduce severe decoherence (T2), cryogenic I/O congestion, and non-deterministic queuing latencies. Furthermore, exposing intra-data-center quantum optical channels to external multiplexers creates catastrophic physical-layer vulnerability to state exfiltration and covert decoherence sabotage. This monograph establishes a unified, physical-layer networking architecture for planetary-scale quantum data centers: (1) PHOENIX_ROUTER, a strict-sense non-blocking multi-stage optical switching fabric constructed from sub-nanosecond thin-film lithium niobate (TFLN) and barium titanate (BTO) Mach-Zehnder interferometers, executing zero-buffer cut-through entanglement distribution at 1550 nm; (2) a dynamic Cut-Through Entanglement Swapping Protocol that eliminates quantum memory dependencies by synchronizing Bell-state measurements (BSM) directly on flying photonic states, achieving an end-to-end distributed Bell fidelity FBell >= 0.978 with latency under 2.2 microseconds; and (3) a Physical-Layer Determinism Firewall (DFW) that continuously executes real-time Clauser-Horne-Shimony-Holt (CHSH) Bell tests to detect channel tampering, driving an electro-optic Pockels shutter in < 8 ns to physically isolate compromised cryostats. We derive the non-blocking permutation group theorems, optical Hamiltonian dissipation dynamics, and corporate board liability alignments under the Delaware Caremark Standard, establishing a verifiable blueprint for secure, distributed quantum infrastructure.