Toward 1% single-photon anharmonicity with periodically poled lithium niobate microring resonators

The absence of the single-photon nonlinearity has been a major roadblock in developing quantum photonic circuits at optical frequencies. In this paper, we demonstrate a periodically poled thin film lithium niobate microring resonator (PPLNMR) that reaches 5,000,000%/W second-harmonic conversion efficiency-almost 20-fold enhancement over the state-of-the-art-by accessing its largest chi((2)) tensor component d(33) via quasi-phase matching. The corresponding single-photon coupling rate g/2 pi is estimated to be 1.2 MHz, which is an important milestone as it approaches the dissipation rate kappa/2 pi of best-available lithium niobate microresonators developed in the community. Using a figure of merit defined as g/kappa, our device reaches a single-photon nonlinear anharmonicity approaching 1%. We show that, by further scaling of the device, it is possible to improve the single-photon anharmonicity to a regime where photon blockade effect can be manifested. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement