Collective coherent scattering from quantum dots in a photonic crystal waveguide*

The light-matter interface of a coherent field scattering from a quantum dot coupled to a nanophotonic waveguide enables efficient nonlinear photon-photon interactions and the realization of exotic states of light, such as two-photon bound states. The exploration of collective quantum phenomena with multiple dots within a waveguide is also of great interest, but the spectral inhomogeneity of quantum dots has been a persistent challenge. We overcome this inhomogeneity by strain-tuning InAs quantum dots into resonance, and experimentally demonstrate collective coherent scattering in a photonic crystal waveguide. We show that collective scattering results in an enhanced optical nonlinearity, demonstrated with both the intensity and photon statistics of transmitted coherent light. In addition to providing a means of manipulating quantum optical nonlinearities, collective coherent scattering in this platform may also allow the creation of high-fidelity two-qubit gates, the study of non-Markovian effects, and the creation of subradiant states.