  Topological phase, a novel and fundamental role in matter, displays an
extraordinary robustness to smooth changes in material parameters or disorder.
A crossover between topological physics and quantum information may lead to
inherent fault-tolerant quantum simulations and quantum computing. Quantum
features may be preserved by being encoded among topological structures of
physical evolution systems. This requires us to stimulate, manipulate and
observe topological phenomena at single quantum particle level, which, however,
hasn't been realized yet. Here, we address such a question whether the quantum
features of single photons can be preserved in topological structures. We
experimentally observe the boundary states of single photons and demonstrate
the performance of topological phase on protecting the quantum features in
quasi-periodic systems. Our work confirms the compatibility between macroscopic
topological states and microscopic single photons on a photonic chip. We
believe the emerging 'quantum topological photonics' will add entirely new and
versatile capacities into quantum technologies.
