  Despite its non-Hermitian nature, the transverse optical beam shift exhibits
both real eigenvalues and non-orthogonal eigenstates. To explore this
unexpected similarity to typical PT (parity-time)-symmetric systems, we first
categorize the entire parametric regime of optical beam shifts into Hermitian,
PT-unbroken, and PT-broken phases. Besides experimentally unveiling the
PT-broken regime, crucially, we illustrate that the observed PT-transition is
rooted in the momentum-domain inhomogeneous polarization transformation of the
beam. The correspondence with a typical non-Hermitian photonic system is
further established. Our work not only resolves a longstanding fundamental
issue in the field of optical beam shift but also puts forward the notion of
novel non-Hermitian spin-orbit photonics: a new direction to study
non-Hermitian physics through the optical beam shifts.
