  The integration of quantum emitters within topological nano-photonic devices
opens up new avenues for the control of light-matter interactions at the single
photon level. Here, we realise a spin-dependent, chiral light-matter interface
using individual semiconductor quantum dots embedded in a topological add-drop
filter. The filter is imprinted within a valley-Hall photonic crystal (PhC)
membrane and comprises a resonator evanescently coupled to a pair of access
waveguides. We show that the longitudinal modes of the resonator enable the
filter to perform wavelength-selective routing of light, protected by the
underlying topology. Furthermore, we demonstrate that for a quantum dot located
at a chiral point in the resonator, selective coupling occurs between
well-defined spin states and specific output ports of the topological device.
This behaviour is fundamental to the operation of chiral devices such as a
quantum optical circulator. Our device therefore represents a
topologically-protected building block with potential to play an enabling role
in the development of chiral integrated quantum photonic circuits.
