  Many novel properties of non-Hermitian systems are found at or near the
exceptional points-branch points of complex energy surfaces at which
eigenvalues and eigenvectors coalesce. In particular, higher-order exceptional
points can result in optical structures that are ultrasensitive to external
perturbations. Here we show that an arbitrary order exceptional point can be
achieved in a simple system consisting of identical resonators placed near a
waveguide. Unidirectional coupling between any two chiral dipolar states of the
resonators mediated by the waveguide mode leads to the exceptional point, which
is protected by the transverse spin-momentum locking of the guided wave and is
independent of the positions of the resonators. Various analytic response
functions of the resonators at the exceptional points are experimentally
manifested in the microwave regime. The enhancement of sensitivity to external
perturbations near the exceptional point is also numerically and analytically
demonstrated.
