High-Q and Maximally Intrinsically Chiral Quasi-Bound States in the Continuum via Generative Adversarial Networks

Resonances combining high Q-factors with maximal intrinsic chirality offer substantial advantages for optical sensing and chiral emission. Yet the conflicting symmetry requirements for achieving these two attributes have made it challenging for current metasurface designs to realize both at once. Under low-loss limit with background transparency, we reveal the resonant contribution within the polarization subspace inherently manifests as a rank-1 projector. The system completely decouples from the opposite polarization when the coupling vector is strictly parallel to a specific circularly polarized eigenstate. Crucially, this behavior is governed solely by the relative amplitude and phase of the coupling vector rather than the absolute radiation intensity. Thus we demonstrate that resonant modes coupled to linearly polarized channels with identical coupling strengths and a phase difference of π/2 can simultaneously yield high Q-factors (reaching 2×10⁵) and extreme circular dichroism (CD, up to 0.98). Additionally, we developed a Generative Adversarial Networks (GAN). Unlike traditional regression methods that merely predict the statistical mean of simple correspondences, the discriminator adversarially compels the generator to capture the complex one-to-many mapping between structures and chiral resonances. Benefiting from the coexistence of high Q-factors and strong CD, the metasurface also realizes an excellent chiral refractive-index sensing, achieving a sensitivity of 105 nm/RIU and a figure of merit (FOM) of 8030. This design establishes a new paradigm for high-performance chiral sensing and polarization-controlled devices.