  Controlling and swapping quantum information in a quantum coherent way
between the microwave and optical regimes is essential for building long-range
superconducting quantum networks but extremely challenging. We propose a hybrid
quantum interface between the microwave and optical domains where the
propagation of a single-photon pulse along a nanowaveguide is controlled in a
coherent way by tuning electromagnetically induced transparency window with the
quantum state of a flux qubit. The qubit can route a single-photon pulse with a
single spin in nanodiamond into a quantum superposition of paths without the
aid of an optical cavity - simplifying the setup. By preparing the flux qubit
in a superposition state our cavity-less scheme creates a hybrid state-path
entanglement between a flying single optical photon and a static
superconducting qubit, and can conduct heralded quantum state transfer via
measurement.
