Fault-tolerant interfaces for modular quantum computing on diverse qubit platforms

Modular architectures offer a scalable path toward fault-tolerant quantum computing by interconnecting smaller quantum processing units provided that high-rate, fault-tolerant interfaces can be realized across modules. We present a comprehensive analysis and comparison of known methods for establishing such interfaces, including lattice surgery, transversal gates, and grow-and-distill protocols based on code growing and logical distillation. Using the surface code, we identify optimal interface strategies across a wide range of hardware parameters, such as gate fidelities, entangling rates, and memory resources, and estimate the requirements to achieve logical error rates of 10^{−6} and 10^{−12}. Our results establish when the interface becomes a bottleneck in the computation and provide guidance for experimental implementations with superconducting, atomic, and solid-state hardware.