The Pangaea Architecture: Fault-Tolerant Heterogeneous Topological Codes via a Quantum Bus
We introduce Pangaea, a fault-tolerant quantum architecture that uses a quantum bus to mediate logical operations between remote patches of two-dimensional topological codes. The bus is an auxiliary gauge-code strip whose measurements reconstruct joint logical operators while preserving nearest-neighbor physical connectivity. Enabling native heterogeneous topological codes and multi-qubit Pauli operations, the quantum bus can be interpreted as a three-dimensional generalization of lattice surgery. We require only $O(dN_L)$ physical qubits to implement multi-qubit interactions for $N_L$ distance-$d$ logical qubits, compared to $O(d^2N_L)$ of traditional two-dimensional architectures. At the 50-logical-qubit scale, Pangaea uses up to $10\times$ fewer physical qubits than planar surface-code architectures at matched logical error rates. We verify fault-tolerance of long-range measurement-based CNOT primitives for both surface--surface and surface--color joint parity measurements using pseudo-threshold simulations. We use this protocol to construct a native heterogeneous 15-to-1 magic-state distillation module using the quantum bus. These results establish Pangaea as a scalable architecture for three-dimensional fault-tolerant quantum computing that resolves the routing bottleneck of planar lattice surgery.