Linear-optical programmable quantum router

Chang-Cheng Qu, Lan Zhou, Yu‐Bo Sheng

Yewang Chen, Qing Lin

Jinsong Kuang, Xiaoyang Fang, Jie Zhou +2 more

In this paper, we propose a linear optical implementation scheme of the quantum router. A programming unit is designed. The quantum router makes use of devices which are experimentally realized easily. The signal can be routed into a superposition of output modes through the routing operation, and the spatial degree of freedom of each output mode is related to the control parameter. In addition, the strategy of multistage routing is also exploited on the basis of this router model, and it can exponentially expand the number of output ports. The quantum router is deterministic, rather than probabilistic, no matter how many output ports the quantum router has.

Karel Lemr, Karol Bartkiewicz, Antonín Černoch +1 more

An all-linear-optical scheme for a fully featured quantum router is presented. This device directs the signal photonic qubit according to the state of one control photonic qubit. In the introduction we formulate the list of requirements imposed on a fully quantum router. Then we describe our proposal, showing the exact principle of operation on a linear-optical scheme. Subsequently we provide a generalization of the scheme in order to optimize the success probability by means of a tunable controlled-phase gate. Finally, we show how one can modify the device to route multiple signal qubits using the same control qubit.

Karol Bartkiewicz, Antonín Černoch, Karel Lemr

For several decades, scientists have been aware of significant benefits allowing quantum information processing technologies to surpass their classical counterparts. Recent technological development allows these benefits to be tested experimentally and in some cases also implemented in practical devices. So far the majority of experimental quantum networks was limited to peer-to-peer communications between two parties. Practical implementation of quantum communications networks, however, needs to address the problem of scalability to serve large numbers of users. Similarly to classical computer networks, their quantum counterparts would require routing protocols to direct the signal from its source to destination. Devices implementing these routing protocols are called quantum routers and have recently been subject of an intense research. In this paper, we report on experimental implementation of a linear-optical quantum router. Our device allows single-photon polarization-encoded qubits to be routed coherently into two spatial output modes depending on the state of two identical control qubits. The polarization qubit state of the routed photon is maintained during the routing operation. The success probability of our scheme can be increased up to 25% making it the most efficient linear-optical quantum router developed to this date.

Saroch Leedumrongwatthanakun, Luca Innocenti, Hugo Defienne +4 more