Transduction-Enabled Superconducting Quantum Repeater: Toward Deterministic Entanglement Distribution with High-Fidelity Gates

Long-distance quantum communication is fundamentally limited by photon loss in optical fibers and the no-cloning theorem. Traditional quantum repeater protocols rely on optical Bell state measurements (BSMs), which are inherently probabilistic and limited to a 50% success rate. This paper introduces the Transduction-Enabled Superconducting Quantum Repeater (TESQR), a hybrid architecture that combines the high-speed transmission of photonic qubits with the high-fidelity processing capabilities of superconducting circuits.

The TESQR node functions by converting incoming optical photons into microwave photons using a quantum transducer. Once converted, these signals are coupled directly to a superconducting quantum processing unit (QPU). By performing entanglement swapping locally on the QPU using deterministic microwave gates (CNOT and Hadamard) and measurements, the architecture avoids the probabilistic bottlenecks of linear-optical BSMs. The authors also integrate an entanglement purification scheme directly into the superconducting QPU to further enhance the fidelity of the distributed entangled states.

The study demonstrates that the TESQR framework is operationally deterministic within specific parameter regimes, as it always yields a final state at the remote nodes rather than aborting on photon loss. Numerical simulations using the QuTiP environment show that the TESQR scheme improves the entanglement distribution rate by an average of 63% (and up to 159%) compared to purely photonic architectures. Furthermore, by applying a single round of entanglement purification, the end-to-end fidelity exceeds 0.8 over distances up to 20 km, confirming the feasibility of the hybrid approach for future quantum internet applications.

This work provides a concrete roadmap for integrating superconducting quantum computers into long-distance quantum networks. By shifting the burden of entanglement swapping from fragile optical interference to robust microwave-domain processing, the TESQR architecture offers a path toward higher-rate, higher-fidelity quantum communication that is less sensitive to the inherent limitations of linear optics.