Mechanically mediated optical-microwave quantum state transfer by feedback

TL;DR

This paper demonstrates a broadband, feedback-based quantum state transfer between optical and microwave fields via a mechanical resonator, relaxing previous constraints and enabling scalable quantum networks.

Contribution

It introduces a novel protocol combining broadband, sideband-unresolved cavities with feedback for quantum state transfer, enhancing scalability and noise performance.

Findings

Continuous optical-to-microwave quantum state transfer is achievable with feedback.

Bidirectional transfer is enabled by all-optical coherent feedback.

Quantum transfer witness $ ext{W}_T$ effectively assesses channel performance.

Abstract

State transfer between light and microwaves is a key challenge in quantum networks. Promising transducers use a mechanical intermediary that couples to both fields via radiation pressure. Such electro-optomechanical devices have achieved high efficiencies, yet require resolved-sideband cavities, and generally compromise in scalability and noise performance. Here, we relax this constraint by extending the protocol of Navarathna et al. that transfers optical quantum information onto a mechanical resonator using a broadband, sideband-unresolved cavity and feedback. Combining this with parametric mechanical-to-microwave conversion, we show that continuous optical-to-microwave quantum state transfer is possible using measurement-based feedback, while all-optical coherent feedback enables bidirectional transfer. To assess the transfer, we introduce the quantum transfer witness $\mathcal{W}_T$, which -- though similar to the input-referred added noise -- also identifies whether a channel is capable of both preserving Gaussian entanglement and outperforming classical transduction schemes. Finally, we show that quantum-compatible noise performance is within reach of current experimental capabilities. Our results unlock a new design space for electro-optomechanical transducers and strengthens their candidacy as scalable quantum links between distant nodes.