Telecom-wavelength quantum memories in rare earth ion-doped materials for quantum repeaters

Abstract

The quantum internet, when finally deployed, will enable a plethora of new applications such as theoretically proven secure communication and networked quantum computing, much the same as its classical counterpart whose development began back in the 1990’s. The task of creating a globe-spanning quantum network, however, is proving a rather difficult task due to the detrimental effect of loss on photon transmission. This problem can in theory be solved using so-called quantum repeaters. In one of the most well-known configurations, the long-distance span is divided into smaller segments—so called elementary links—at whose ends pairs of entangled photons are generated. One photon per pair is stored in a quantum memory, and the second member is transmitted via optical fiber to a remote measurement stations positioned at the centre of the segment. There, a joint measurement of the two photons, one from each end, then heralds the distribution of entanglement between the two quantum memories, i.e. heralds entanglement over the elementary link. In the final step, all neighbouring links are combined via a second joint measurement, and end-to-end entanglement is created...