For the purposes of calculation of the unitary evolution of the one-photon electromagnetic field state, the refractive index is exactly the same as for a classical field. As a quantum state, such an EM field propagating in matter is simply a quantum superposition of a one photon free EM field state and excited matter states. The EM field is coupled to the excited states of all the matter atoms / molecules at once in superposition. See my answer here or here for more details on these issues.

As BoyFarrell's Answer says, the actual reflexion, as measured by a light detector, is probabilistic, with each launched photon having a probability of being reflected and detected (assuming the detection aperture is big enough) of a value given by the Fresnel-equation caclculated reflexion to incident intensity ratio.

For the purposes of calculation of the unitary evolution of the one-photon electromagnetic field state, the refractive index is exactly the same as for a classical field. As a quantum state, such an EM field propagating in matter is simply a quantum superposition of a one photon free EM field state and excited matter states. The EM field is coupled to the excited states of all the matter atoms / molecules at once in superposition. See my answer here or here for more details on these issues.

As BoyFarrell's Answer says, the actual reflexion, as measured by a light detector, is probabilistic, with each launched photon having a probability of being reflected and detected (assuming the detection aperture is big enough) of a value given by the Fresnel-equation caclculated reflexion to incident intensity ratio.