  Realizing a fully connected network of quantum processors requires the
ability to distribute quantum entanglement. For distant processing nodes, this
can be achieved by generating, routing, and capturing spatially entangled
itinerant photons. In this work, we demonstrate the deterministic generation of
such photons using superconducting transmon qubits that are directly coupled to
a waveguide. In particular, we generate two-photon N00N states and show that
the state and spatial entanglement of the emitted photons are tunable via the
qubit frequencies. Using quadrature amplitude detection, we reconstruct the
moments and correlations of the photonic modes and demonstrate state
preparation fidelities of $84\%$. Our results provide a path towards realizing
quantum communication and teleportation protocols using itinerant photons
generated by quantum interference within a waveguide quantum electrodynamics
architecture.
