Communication networks have transformed our society over the past half century, and we can scarcely imagine our daily lives without them. Recent advances in the emergent field of quantum technologies have exhilarated scientists about the possibility of linking quantum devices in networks. Long-distance quantum communication portends functionality that is beyond the reach of classical networks [1]. To make full use of entanglement and other quantum effects, quantum networks exchange signals at the level of single photons. As a result, attenuation in fiber is the dominant source of error in these systems. Photon loss, however, can be remedied using a set of intermediate network nodes, called quantum repeaters, which create a direct entangled connection between distant network nodes [2]. A quantum repeater based on nitrogen-vacancy centers in diamond recently achieved the entanglement of two network nodes separated by a distance of 32 m [3]. Now Victor Krutyanskiy of the University of Innsbruck in Austria and colleagues implemented a quantum repeater using trapped ions, which they employed to splice two independent 25-km-long entangled links into a single 50-km-long connection [4] (Fig. 1). This distance is of the order required by practical quantum networks in the real world.
To read more, click here.