  We identify a general connection between the physics of exceptional points in
non-Hermitian systems and the few-photon bound states in waveguide quantum
electrodynamics (QED) systems. We show that, in waveguide QED systems where the
local quantum system exhibits an exceptional point, the tightest-bound
few-photon bound state occurs at the exceptional point. We illustrate this
connection with an explicit computation on a waveguide QED system in which a
waveguide is coupled to a Jaynes-Cummings system. Our result provides a quantum
signature of the exceptional point physics and indicates that the physics of
exceptional point can be used to understand and control the photon-photon
interaction.
