Towards on-chip cavity-enhanced microwave to optical conversion using erbium doped crystals*

Generating remote entanglement between distant superconducting circuits via optical photons represents a crucial milestone towards the development of future quantum networks. Ensembles of rare-earth ions (REIs) coupled to optical and microwave cavities offer a promising architecture to achieve bidirectional coherent microwave to optical conversion by harnessing the strong coupling of REI ensembles to microwave and optical fields.
Here, we present an integrated platform composed of a superconducting microwave resonator and an amorphous silicon photonic resonator coupled to an erbium ensemble doped in the yttrium orthosilicate substrate. Our platform enables resonators with high quality factors in both the optical and microwave domain, while maintaining sufficient overlap between the optical and microwave fields required for the magneto-optical converter to achieve high efficiency. We present the fabrication of optical and microwave resonators and characterization of the platform's metrics such as microwave resonator losses due to static magnetic fields and circulating optical photons in the optical resonator.