A frequency-agile microwave-optical interface for superconducting qubits

TL;DR

This paper introduces a frequency-agile microwave-optical interface that enables broadband, tunable transduction for superconducting qubits, facilitating scalable quantum networks over optical fibers.

Contribution

It presents a cascaded, tunable M2O and M2M transducer architecture that covers a 3.5 GHz frequency range, overcoming narrow bandwidth limitations of previous devices.

Findings

Achieved continuous frequency coverage from 5.0 to 8.5 GHz.

Demonstrated optical readout of a superconducting qubit detuned by 1.7 GHz.

Showcased scalable fiber-linked superconducting quantum nodes.

Abstract

Superconducting quantum processors operate at microwave frequencies in millikelvin environments, making it challenging to interconnect distant nodes using conventional microwave wiring. Coherent microwave-to-optical (M2O) transduction enables superconducting quantum networks by interfacing itinerant microwave photons with low-loss optical fiber. However, many state-of-the-art transducers provide efficient conversion only over a narrow frequency span, complicating deployment with heterogeneous superconducting devices that are detuned by gigahertz-scale offsets. Here we demonstrate a frequency-agile microwave-optical interface that overcomes this bandwidth mismatch by cascading an electro-optic M2O transducer with a multimode microwave-to-microwave (M2M) frequency converter, with in situ tunability of the microwave resonances in both stages. Using this architecture, we realize continuous frequency coverage from 5.0 to 8.5 GHz within a single system. As an application relevant to superconducting-qubit networking, we use the cascaded M2M-M2O interface to optically read out a superconducting qubit whose readout resonator is detuned by 1.7 GHz from the native M2O microwave resonance, demonstrating a scalable route toward fiber-linked superconducting quantum nodes.