  The realization of robust strong coupling and entanglement between distant
quantum emitters (QEs) is very important for scalable quantum information
processes. However, it is hard to achieve it based on conventional systems.
Here, we propose theoretically and demonstrate numerically a scheme to realize
such strong coupling and entanglement. Our scheme is based on the photonic
crystal platform with topologically protected edge state and zero-dimensional
topological corner cavities. When the QEs are put into topological cavities,
the strong coupling between them can be fulfilled with the assistance of the
topologically protected interface state. Such a strong coupling can maintain a
very long distance and be robust against various defects. Especially, we
numerically prove that the topologically protected entanglement between two QEs
can also be realized. Moreover, the duration of quantum beats for such
entanglement can reach several orders longer than that for the entanglement in
a conventional photonic cavity, making it be very beneficial for a scalable
quantum information process.
