Few-photon routing via chiral light-matter couplings

A quantum router is one of the essential elements in the quantum network.Conventional routers only direct a single photon from one quantum channel into another.Here,we propose a fewphoton router.The active element of the router is a single qubit chirally coupled to two independent waveguides simultaneously,where each waveguide mode provides a quantum channel.By introducing the operators of the scatter-free space and the controllable space,the output state of the one-photon and two-photon scattering are derived analytically.It is found that the qubit can direct one and two photons from one port of the incident waveguide to an arbitrarily selected port of the other waveguide with unity,respectively.However,two photons cannot be simultaneously routed to the same port due to the anti-bunch effect.