The rapid development of superconducting quantum hardware is expected to run into significant I/O restrictions due to the need for large-scale error correction in a cryogenic environment. Photonics could be the key to both, i.e. optical multiplexing of many control and readout lines on the one hand, but also to realize distributed quantum computing with modules of manageable size each. We have developed an electro-optic interconnect that facilitates strong interactions between microwave and telecom wavelength light. It operates close to the quantum limit and offers new perspectives for a number of scaling, networking and sensing applications. We demonstrate ultra-low noise wavelength conversion, entanglement of microwave and optical fields, as well as an all-optical superconducting qubit readout that does not require any of the bulky cryogenic microwave components.