  Parity-time (PT)-symmetric Hamiltonians have widespread significance in
non-Hermitian physics. A PT-symmetric Hamiltonian can exhibit distinct phases
with either real or complex eigenspectrum, while the transition points in
between, the so-called exceptional points, give rise to a host of critical
behaviors that holds great promise for applications. For spatially periodic
non-Hermitian systems, PT symmetries are commonly characterized and observed in
line with the Bloch band theory, with exceptional points dwelling in the
Brillouin zone. Here, in nonunitary quantum walks of single photons, we uncover
a novel family of exceptional points beyond this common wisdom. These
"non-Bloch exceptional points" originate from the accumulation of bulk
eigenstates near boundaries, known as the non-Hermitian skin effect, and
inhabit a generalized Brillouin zone. Our finding opens the avenue toward a
generalized PT-symmetry framework, and reveals the intriguing interplay between
PT symmetry and non-Hermitian skin effect.
