  The quantum entanglement between two qubits is crucial for applications in
the quantum communication. After the entanglement of photons was experimentally
realized, much effort has been taken to exploit the entangled electrons in
solid-state systems. Here, we propose a Cooper-pair splitter, which can
generate spatially-separated but entangled electrons, in a quantum anomalous
Hall insulator proximity-coupled with a superconductor. After coupling with a
superconductor, the chiral edge states of the quantum anomalous Hall insulator
can still survive, making the backscattering impossible. Thus, the local
Andreev reflection becomes vanishing, while the crossed Andreev reflection
becomes dominant in the scattering process. This indicates that our device can
serve as an extremely high-efficiency Cooper-pair splitter. Furthermore,
because of the chiral characteristic, our Cooper-pair splitter is robust
against disorders and can work in a wide range of system parameters.
Particularly, it can still function even if the system length exceeds the
superconducting coherence length.
