Multimode all-optical EPR steering swapping via atomic coherence-mediated four-wave mixing

Einstein-Podolsky-Rosen (EPR) steering, a distinct class of quantum correlation intermediate between entanglement and Bell nonlocality, exhibits unique asymmetry and directionality. EPR steering swapping, analogous to entanglement swapping, enables two initially independent particles to establish EPR steering correlations. Recent advances in all-optical entanglement and EPR steering swapping have overcome the limitation of mutual electro-optical conversions. However, for quantum information systems required in real-world applications, extending these capabilities to multimode regimes remains largely underexplored. Here, we propose an m-to-n multimode all-optical EPR steering swapping architecture based on energy-level-cascaded four-wave mixing processes. By harnessing fundamental light-atom interactions, we demonstrate scalable multimode EPR steering swapping and realize non-Hermitian control over dressing-induced coherent channels. Crucially, our multimode approach demonstrates distinctive, mode-dependent features of non-monotonicity and asymmetry, which are unattainable in conventional two-mode schemes. The flexible controllability afforded by such multimode quantum correlations also facilitates interfaces between non-Hermitian light-matter systems, paving the way for practical implementations of EPR steering and all-optical quantum networks.