Parity-time-symmetry-enabled broadband quantum frequency-comb generation

Microcavities stand out as competitive tools in the development of quantum frequency combs (QFCs) for multiphoton entanglement sources, frequency-multiplexed single-photon sources, and the generation of high-dimensional entangled states. However, the presence of waveguide dispersion hinders the creation of broadband QFCs, an issue that becomes increasingly critical as the quality factor of the microcavity increases. Here, we present a scheme to enhance the spectral range of QFCs by selectively manipulating the pump resonance via parity-time symmetry. We show that by using pulsed pump light to cover the pump resonance, frequency-matching conditions can be relaxed and the spectral range of QFCs can thus be significantly extended near the exceptional point. The proposed method offers a simple, effective, and robust approach to increase the dimension of QFCs, without severely sacrificing nonlinear efficiency.