Chip-to-chip hyperentanglement distribution and entanglement purification using silicon integrated photonics

Quantum repeaters are employed in quantum communication to overcome the long-distance transmission loss of quantum states. The quantum repeater is based on various key technologies, including quantum entanglement swapping, quantum memory, and entanglement purification. In particular, quantum purification can distil high-quality entanglement from the degraded entangled states which is propagating through noisy quantum communication channels. Although previous reports have demonstrated on-chip entanglement swapping and teleportation through the less-noisy channel, current entanglement purification experiments still rely on off-chip discrete devices, leading to limitations on scalability, stability, and controllability. In this paper, for the first time, we demonstrated chip-to-chip hyperentanglement distribution and quantum entanglement purification based on integrated silicon chips. Path-encoded high-dimensional entangled photon pairs are produced on the chip, converted to fibre-based polarization-spatial hyperentanglement by grating couplers, distributed to the receiver silicon chip, and finally purified by consuming the spatial degree of freedom. Our purification scheme by integrated photonics finished the last puzzle of on-chip quantum repeater, which will promote the realization of the quantum repeater based on integrated photonics.