Dynamical photon–photon interaction mediated by a quantum emitter

Single photons role in the development of quantum science and technology. They can carry quantum information over extended distances to act as the backbone of a future quantum internet1 and can be manipulated in advanced photonic circuits, enabling scalable photonic quantum computing2,3. However, more sophisticated devices and protocols need access to multi-photon states with particular forms of entanglement. Efficient light–matter interfaces offer a route to reliably generating these entangled resource states4,5. Here we utilize the efficient and coherent coupling of a single quantum emitter to a nanophotonic waveguide to realize a quantum nonlinear interaction between single-photon wavepackets. We demonstrate the control of a photon using a second photon mediated by the quantum emitter. The dynamical response of the two-photon interaction is experimentally unravelled and reveals quantum correlations controlled by the pulse duration. Further development of this platform work, which constitutes a new research frontier in quantum optics6, will enable the tailoring of complex photonic quantum resource states. Efficient interactions between two photons is a challenging requirement for quantum information processing. A quantum dot coupled to a waveguide produces strong interactions that can induce photon correlations and reshape two-photon wavepackets.