Hybrid microwave-optical scanning probe for addressing solid-state spins in nanophotonic cavities

TL;DR

This paper introduces a fiber-based scanning probe that efficiently couples light and microwave radiation into nanophotonic devices at cryogenic temperatures, enabling advanced control of solid-state spins for quantum applications.

Contribution

The work presents a novel hybrid microwave-optical scanning probe capable of operating inside cryostats, combining high optical coupling efficiency with strong microwave magnetic fields.

Findings

Achieved 46% optical coupling efficiency in the probe.

Delivered up to 9 Gauss microwave magnetic field.

Demonstrated control of Er$^{3+}$ ions in silicon nanophotonics.

Abstract

Spin-photon interfaces based on solid-state atomic defects have enabled a variety of key applications in quantum information processing. To maximize the light-matter coupling strength, defects are often placed inside nanoscale devices. Efficiently coupling light and microwave radiation into these structures is an experimental challenge, especially in cryogenic or high vacuum environments with limited sample access. In this work, we demonstrate a fiber-based scanning probe that simultaneously couples light into a planar photonic circuit and delivers high power microwaves for driving electron spin transitions. The optical portion achieves 46% one-way coupling efficiency, while the microwave portion supplies an AC magnetic field with strength up to 9 Gauss. The entire probe can be scanned across a large number of devices inside a $^3$He cryostat without free-space optical access. We demonstrate this technique with silicon nanophotonic circuits coupled to single Er$^{3+}$ ions.