  We propose an integrated photonics device for mapping qubits encoded in the
polarization of a photon onto the spin state of a solid-state defect coupled to
a photonic crystal cavity: a `Polarization-Encoded Photon-to-Spin Interface'
(PEPSI). We perform a theoretical analysis of the state fidelity's dependence
on the device's polarization extinction ratio and atom-cavity cooperativity.
Furthermore, we explore the rate-fidelity trade-off through analytical and
numerical models. In simulation, we show that our design enables efficient,
high fidelity photon-to-spin mapping.
