ALP Seminar: Correlating photons using the collective nonlinear response of atoms weakly coupled to an optical mode

Non-classical states of light – such as single photons or entangled photon pairs – are a key resource for quantum science and technology, and their generation is a very active area of research. In this context, it has been predicted that resonant laser light, when simply transmitted through an ensemble of two-level emitters, can evolve into a quantum-correlated state of light [Phys. Rev. Lett. 121, 143601 (2018)]. According to this work, the weak nonlinear response of the individual emitters can be collectively enhanced, leading to a correlated transport of photons through the ensemble. Using laser-cooled atoms that are trapped and optically interfaced with a nanophotonic waveguide, this effect has recently been demonstrated by our group. Depending on the experimental parameters, the output light exhibits photon bunching and anti-bunching [Nat. Photonics 14, 719 (2020); Phys. Rev. Lett. 131, 183601 (2023)] or quadrature squeezing [Phys. Rev. Lett. 127, 123602 (2021)], while maintaining excellent coherence properties and indistinguishability. My talk will introduce this new mechanism of nonlinear photon transport and discuss its future applications.