Proposal for Superconducting Quantum Networks Using Multi-Octave Transduction to Lower Frequencies

TL;DR

This paper proposes a novel method for superconducting quantum networks that transduces high-frequency excitations to lower frequencies to reduce noise and losses, enabling long-distance quantum communication.

Contribution

It introduces the multi-octave asymmetrically threaded SQUID circuit (MOATS) for efficient transduction across a broad frequency range, facilitating kilometer-scale quantum links.

Findings

Achieves single-photon fidelity of 0.962 at 200 MHz

Doubles the quantum channel capacity lower bound

Enables long-distance quantum communication with high fidelity

Abstract

We propose networking superconducting quantum circuits by transducing their excitations (typically 4-8 GHz) to 100-500 MHz photons for transmission via cryogenic coaxial cables. Counter-intuitively, this frequency downconversion reduces noise and transmission losses. We introduce a multi-octave asymmetrically threaded SQUID circuit (MOATS) capable of the required efficient, high-rate transduction. For a 100-meter cable with $Q_i = 10^5$ at 10 mK, our approach achieves single-photon fidelities of 0.962 at 200 MHz versus 0.772 at 8 GHz, and triples the lower bound on quantum channel capacity. This method enables kilometer-scale quantum links while maintaining high fidelities, combining improved performance with the practical advantages of flexible, compact coaxial cables.