Routing entanglement in the quantum internet

Remote quantum entanglement can enable numerous applications including distributed quantum computation, secure communication, and precision sensing. We consider how a quantum network—nodes equipped with limited quantum processing capabilities connected via lossy optical links—can distribute high-rate entanglement simultaneously between multiple pairs of users. We develop protocols for such quantum “repeater” nodes, which enable a pair of users to achieve large gains in entanglement rates over using a linear chain of quantum repeaters, by exploiting the diversity of multiple paths in the network. Additionally, we develop repeater protocols that enable multiple user pairs to generate entanglement simultaneously at rates that can far exceed what is possible with repeaters time sharing among assisting individual entanglement flows. Our results suggest that the early-stage development of quantum memories with short coherence times and implementations of probabilistic Bell-state measurements can have a much more profound impact on quantum networks than may be apparent from analyzing linear repeater chains. This framework should spur the development of a general quantum network theory, bringing together quantum memory physics, quantum information theory, quantum error correction, and computer network theory. Quantum internet: all roads lead to entanglement distribution The best way to generate entanglement between two distant users in a quantum network is to look at many paths at the same time. Saikat Guha from University of Arizona led a team of American researchers which discovered an improved way to tackle the task of entanglement distribution. What they found is that, even in the case of only two users, having a network of links and using a multi-path strategy instead of a simple sequence of segments gives a large advantage in terms of achievable distance. The problem of generating entanglement (the notorious ‘spooky' quantum correlations) between distant locations is not only a matter of fundamental science, but it would allow to empower the Internet with a set of quantum-enhanced capabilities such as intrinsically-secure communication.