Higher-order exceptional points in a non-reciprocal quantum waveguide beam splitter

Non-Hermitian photonic systems, characterized by controlled gain and loss, exhibit exceptional points (EPs) where eigenvalues and eigenvectors coalesce. Quantum systems hosting EPs display enhanced sensitivity to external perturbations, which increases with the order of the EP. Consequently, higher-order EPs hold great potential for advanced sensing applications, though they are challenging to realize due to stringent symmetry requirements. In our talk, we realize and analyze higher-order EPs in a quantum waveguide beam splitter using both analytical modeling and numerical simulations. By introducing asymmetric coupling, we demonstrate that higher-order EPs can emerge even in the absence of dissipation, overcoming long-standing challenges associated with symmetry fine-tuning. Furthermore, we investigate the evolution of NOON states under activated non-reciprocity, revealing its impact on quantum dynamics. Our results highlight the versatility of non-reciprocal photonic platforms in engineering higher-order EPs, offering new opportunities for advanced interferometric systems, quantum state control, and next-generation sensing technologies.