Nonlinear Quantum Photonics from Reflecting Coherent Light off a Tin-Vacancy Center in a Diamond Waveguide

Strong interaction between single photons and material qubit systems is a key element for quantum information science and technology, and in particular for photon-mediated entanglement generation between remote quantum systems. Diamond Group-IV-vacancy color centers are one of the leading platforms for realizing efficient spin qubit-photon interfaces in nanophotonic devices thanks to their protection from charge noise by inversion symmetry. In particular, the Tin-Vacancy center (SnV) has emerged as a high potential candidate towards scalable diamond integrated devices. The SnV offers excellent spin coherence at temperatures around 1K and high quantum efficiency which can provide efficient coupling to light with lower requirements on the nanophotonic device properties and operating temperature than the more established diamond SiV center.



Here we present our work on SnV centers integrated in nanophotonic diamond waveguides. We show high stability of the optical transition and efficient coupling of a single SnV to the waveguide optical mode, leading to a coherent extinction of the transmission of up to 25%. We demonstrate tuneable interference of the reflected single-photon field with a coherent state. Finally, we investigate how a single SnV alters the photon statistics of a coherent input state, both in reflection and transmission, proving the strong nonlinearity at the single photon level.