  We propose and analyze a scalable and fully autonomous scheme for preparing
spatially distributed multiqubit entangled states in a dual-rail waveguide QED
setup. In this approach, arrays of qubits located along two separated
waveguides are illuminated by correlated photons from the output of a
nondegenerate parametric amplifier. These photons drive the qubits into
different classes of pure entangled steady states, for which the degree of
multipartite entanglement can be conveniently adjusted by the chosen pattern of
local qubit-photon detunings. Numerical simulations for moderate-sized networks
show that the preparation time for these complex multiqubit states increases at
most linearly with the system size and that one may benefit from an additional
speedup in the limit of a large amplifier bandwidth. Therefore, this scheme
offers an intriguing new route for distributing ready-to-use multipartite
entangled states across large quantum networks, without requiring any precise
pulse control and relying on a single Gaussian entanglement source only.
