Hardware-Efficient Bosonic Module for Entangling Superconducting Quantum Processors via Optical Networks

TL;DR

This paper introduces a modular, optical interconnect architecture for superconducting quantum processors that enables long-distance entanglement with high fidelity, overcoming integration challenges of microwave-to-optical transducers.

Contribution

It presents a novel SNAIL-based parametric coupling interface and a cavity-based architecture that improves entanglement fidelity and rate over long distances compared to previous transmon-based methods.

Findings

Achieves raw entangled bit fidelities of ~0.8 at kHz rates over 30 km.

Improves purified fidelities to ~0.94 at 0.2 kHz using asymmetric entanglement pumping.

Demonstrates a practical, scalable approach for distributed superconducting quantum computing.

Abstract

Scaling superconducting quantum processors beyond single dilution refrigerators requires efficient optical interconnects, yet integrating microwave-to-optical (M2O) transducers poses challenges due to frequency mismatches and qubit decoherence. We propose a modular architecture using SNAIL-based parametric coupling to interface Brillouin M2O transducers with long-lived 3D cavities, while maintaining plug-and-play compatibility. Through numerical simulations incorporating realistic noises, including laser heating, propagation losses, and detection inefficiency, we demonstrate raw entangled bit fidelities of F~0.8 at kHz-level rates over 30 km using the Duan-Lukin-Cirac-Zoller (DLCZ) protocol. Implementing asymmetric entanglement pumping tailored to amplitude damping errors, we achieve purified fidelities F~0.94 at 0.2 kHz rates. Our cavity-based approach outperforms transmon schemes, providing a practical pathway for distributed superconducting quantum computing.