Quantum repeaters: Current developments and prospects

We describe principles of operation of a quantum repeater, i.e., a device designed to distribute entangled states of quantum systems over long distances. A review is presented of the latest achievements in the field of experimental implementation of its simplest version (a first-generation quantum repeater) and in the development of its key component (quantum memory). The immediate and long-term prospects for the development of studies in this area are discussed.