  We demonstrate a scheme for in-plane initialization and readout of a single
exciton spin in an InGaAs quantum dot (QD) coupled to a GaAs nanobeam
waveguide. The chiral coupling of the QD and the optical mode of the nanobeam
enables spin initialization and readout fidelity approaching unity in magnetic
field $B=1$ T and $\sim$0.9 without the field. We further show that this
in-plane excitation scheme is independent of the incident excitation laser
polarization and depends solely on the excitation direction. This scheme
provides a robust in-plane spin excitation basis for a photon-mediated spin
network for quantum information applications.
