Non-Hermitian optical parametric systems with anti-parity-time symmetry

Over the past decades, the development of optical parametric amplification (OPA) -based systems has demonstrated excellent performance characteristics in terms of pulse duration, energy, peak power, and repetition rate. However, the studies on OPA typically rely on specific experimental conditions or numerical parameters, limiting the comprehensive understanding of the overall process. In this work, by introducing a new quantum perspective by incorporating non-Hermitian theory into the optical parametric process, we demonstrate the global behaviors of the non-Hermitian optical parametric system in the parametric space, and we categorize such behaviors into four distinct quadrants, depending on whether the anti-parity-time (anti-PT) symmetry is broken and the amplification is present. We observe exceptional surfaces separating the anti-PT exact phase and anti-PT broken phase in the anti-PT symmetric OPAs, and a unique behavior of gain/loss-sgn (phase mismatch) locking indicating the gain phase transition of eigenmodes in the anti-PT symmetry-broken OPAs. In the vicinity around the exceptional points, we observe significant amplification jumps, which are beneficial for experimental observation. Our study demonstrates that lossful OPAs with unique non-Hermitian characteristics provide promising routes for definitely advancing the novel design of ultrabroadband and high efficiency.