Digital switching in the quantum domain

In this paper, we present a switching architecture such that digital data can be switched in the quantum domain. The proposed mechanism supports unicasting as well as multicasting, and is strict-sense nonbiocking. In addition, with appropriate interface conversion, this architecture can also be used to switch classical information. This results in a quantum switch that can be used to build classical and quantum information networks. To present this idea, we define the connection digraph which can be used to describe the behavior of a switch at a given time, then we show how a connection digraph can be implemented using elementary quantum gates. Compared with a traditional space or time domain switch, the proposed switching mechanism is much more scalable. Assuming an n × n quantum switch, the space consumption grows linearly, i.e., O(n), while the time complexity is O (1) for unicasting, and O (log ₂ n) for multicasting. Based on these advantages, a high-throughput switching device can be built simply by increasing the number of I/O ports.