  Quantum entanglement, as the strictly non-classical phenomena, is the kernel
of quantum computing and quantum simulation, and has been widely applied
ranging from fundamental tests of quantum physics to quantum information
processing. The decoherence of quantum states restricts the capability of
building quantum simulators and quantum computers in a scalable fashion.
Meanwhile, the topological phase is found inherently capable of protecting
physical fields from unavoidable fabrication-induced disorder, which inspires
the potential application of topological protection on quantum states. Here, we
present the first experimental demonstration of topologically protected quantum
polarization entangled states on a photonic chip. The process tomography shows
that quantum entanglement can be well preserved by the boundary states even
when the chip material substantially introduces relative polarization rotation
in phase space. Our work links topology, material and quantum physics, opening
the door to wide applications of topological enhancement in genuine quantum
regime.
