Higher-order exceptional lines in a non-Hermitian JaynesCummings triangle

Higher-order exceptional points (EPs) in non-Hermitian systems showcase diverse physical phenomena but require more parameter space freedom or symmetries. It leads to a challenge for the exploration of high-order EP geometries in low-dimensional systems. Here we observe both a third-order exceptional surface and line in a Jaynes-Cummings triangle consisting of three cavities arranged in a ring. A fine-tuning artificial magnetic field dramatically enriches the emergence of the third-order exceptional lines ($3$ELs), which require only three tuning parameters in the presence of chiral symmetry and parity-time (PT) symmetry. Third-order EPs amplify the effect of perturbations through a cube-root response mechanism, displaying a greater sensitivity than second-order EPs. We develop novel fidelity and Loschmidt echo using the associated-state biorthogonal approach, which successfully characterizes EPs and quench dynamics even in PT breaking regime. Our work advances the use of higher-order EPs in quantum technology applications.