Microwave-to-optical conversion with a gallium phosphide photonic crystal cavity

TL;DR

This paper introduces a gallium phosphide photonic crystal cavity platform for microwave-to-optical conversion, leveraging piezoelectric effects and mechanical modes to enable quantum communication between superconducting qubits and optical photons.

Contribution

It presents a novel integrated device combining gallium phosphide photonic cavities with niobium circuits for efficient microwave-to-optical conversion.

Findings

Achieved vacuum optomechanical coupling rates of up to 300 kHz.

Mechanical breathing modes at approximately 3.2 GHz were utilized.

Estimated electromechanical coupling rate of about 200 kHz to superconducting qubits.

Abstract

Electrically actuated optomechanical resonators provide a route to quantum-coherent, bidirectional conversion of microwave and optical photons. Such devices could enable optical interconnection of quantum computers based on qubits operating at microwave frequencies. Here we present a novel platform for microwave-to-optical conversion comprising a photonic crystal cavity made of single-crystal, piezoelectric gallium phosphide integrated on pre-fabricated niobium circuits on an intrinsic silicon substrate. The devices exploit spatially extended, sideband-resolved mechanical breathing modes at $\sim$ 3.2 GHz, with vacuum optomechanical coupling rates of up to $g_0/2\pi \approx$ 300 kHz. The mechanical modes are driven by integrated microwave electrodes via the inverse piezoelectric effect. We estimate that the system could achieve an electromechanical coupling rate to a superconducting transmon qubit of $\sim$ 200 kHz. Our work represents a decisive step towards integration of piezoelectro-optomechanical interfaces with superconducting quantum processors.