Non-Gaussian quantum phenonema in synchronously-pumped optical parametric oscillator

The synchronously-pumped optical parametric oscillator (SPOPO) below threshold has been engineered to generate multimode squeezing and entanglement among the various frequency components of the broadband pulses. A natural question to ask is whether new phenomena exist in the above-threshold regime of the SPOPO. To this end, we have developed a quantum input-output model of the SPOPO that is rigorously valid above threshold. In this model, we have found theoretical evidence of rich multimode non-Gaussian quantum phenomena such as the generation of multimode cat states, which can be engineered by designing the pump spectrum and dispersion of the SPOPO appropriately. We also showed that, consistent with classical intuition, field enhancement due to the localization of the pulse envelope in time enhances the effective nonlinearity by the (large) number of interacting modes. Because of this enhancement, we speculate that non-Gaussian states may be experimentally accessible in the future with near-term, on-chip photonic platforms, such as thin-film lithium niobate.