  We calculate the resonant inelastic X-ray scattering (RIXS) response of the
Kitaev honeycomb model, an exactly solvable quantum-spin-liquid model with
fractionalized Majorana and flux excitations. We find that the fundamental RIXS
channels, the spin-conserving (SC) and the non-spin-conserving (NSC) ones, do
not interfere and give completely different responses. SC-RIXS picks up
exclusively the Majorana sector with a pronounced momentum dispersion, whereas
NSC-RIXS also creates immobile fluxes, thereby rendering the response only
weakly momentum dependent, as in the spin structure factor measured by
inelastic neutron scattering. RIXS can therefore pick up the fractionalized
excitations of the Kitaev spin liquid separately, making it a sensitive probe
to detect spin-liquid character in potential material incarnations of the
Kitaev honeycomb model.
