Cascaded Multi-Level Linear-Optical Quantum Router

Quantum router is the requisite element in the future quantum network. In this paper, we describe an approach for constructing the cascaded multi-level quantum router, which is based on the previous work of Lemr et al. (Phys. Rev. A 87 , 062333 ( 2013 )). We show that the signals in the router output ports of the i th level can be regarded as the input signals of the ( i + 1)th level. In this way, the cascaded multi-level quantum router can be constructed. We can obtain a K level quantum router with 2 K output ports. We also show that with the help of tunable c-phase gate, the success probability of the quantum router can be increased. Moreover, by exploiting the quantum nondemolition (QND) measurement, the control qubits can be reused to decrease the resource of the router. This protocol is useful for future quantum network.