Quantum Source has published a detailed architectural blueprint for fault-tolerant quantum computing that combines photonic qubits for long-range connectivity with cavity-coupled rubidium-87 atoms for near-deterministic entanglement. The core innovation is a reusable unit cell — a single atom trapped in a high-finesse Fabry-Pérot cavity — that performs photon generation, atomic qubit preparation/measurement, and near-deterministic controlled-phase (CZ) entangling gates through photon reflection. By using measurement-based quantum computation on a 3D RHG lattice (a surface code variant), atoms act as reusable stitching points while photons provide unrestricted connectivity. Numerical simulations under a photon-loss noise model yield a fault-tolerance threshold of ~2.6% loss per gate (~15% total). The design avoids dilution refrigerators, eliminates the need for photon indistinguishability, and reduces hardware overhead by over an order of magnitude compared to purely photonic approaches. Significant engineering challenges remain, and experimental validation of the full architecture is still ahead.
