A quantum relay chip based on telecommunication integrated optics technology

We investigate an integrated optical circuit on lithium niobate designed to implement a teleportation-based quantum relay scheme for one-way quantum communication at a telecom wavelength. Such an advanced quantum circuit merges for the first time both optical-optical and electro-optical nonlinear functions necessary for implementing the desired on-chip single-qubit teleportation. On the one hand, spontaneous parametric down-conversion is used to produce entangled photon pairs. On the other, we take advantage of two photon routers, consisting of electro-optically controllable couplers, to separate the paired photons and to carry out a Bell state measurement, respectively. After having validated all the individual functions in the classical regime, we performed a Hong-Ou-Mandel experiment to mimic a one-way quantum communication link. Such a quantum effect, seen as a prerequisite towards achieving teleportation, has been obtained at one of the routers when the chip was coupled to an external single-photon source. The two-photon interference pattern shows a net visibility of 80%, which validates the proof of principle of a 'quantum relay circuit' for qubits carried by telecom photons. In the case of optimized losses, such a chip could increase the maximal achievable distance of one-way quantum key distribution links by a factor of 1.8. Our approach and results emphasize the potential of integrated optics on lithium niobate as a key technology for future reconfigurable quantum information manipulation.