  Coherent quantum control of multiqubit systems represents one of the
challenging tasks in quantum science and quantum technology. Here we
theoretically investigate the reflectivity spectrum in an atom-nanophotonic
cavity with collective nonreciprocal couplings. In the strong-coupling regime
with a high cooperativity, we theoretically predict distinct on-resonance
spectral dips owing to destructive interferences of chiral couplings. Due to
the well-separated multiple dips in the spectrum, a contrasted reflectivity
suggests a new control knob over the desired entangled state preparation. We
propose to utilize such atom-nanophotonic cavity to quantum engineer the atomic
internal states via photon-mediated dipole-dipole interactions and the
chirality of decay channels, where the atomic Bell state and W states for
arbitrary number of atoms can be tailored and heralded by state carving in the
single-photon reflection spectrum. Our results pave the way toward quantum
engineering of multiqubit states and offer new opportunities for coherent and
scalable multipartite entanglement transport in atoms coupled to nanophotonic
devices.
