Quantum-based techniques for transferring and storing information have been demonstrated.

A program of research during the years 2001 through 2006 was devoted to building theoretical and practical foundations for the development of quantum repeaters as means of overcoming losses of photons in long-distance quantum communication systems. The idea underlying this research was to investigate means of utilizing suitably prepared ensembles of atoms (e.g. rubidium vapors) as means of storing and transferring the information encoded in the states of photons. The main accomplishments of this research, in approximate chronological order, include the following:

• Quantum repeaters based on ensembles of atoms, atom-atom correlations mediated by dark-state polaritons, and generation of stationary pulses of light were proposed and analyzed theoretically.
• Experiments were performed to demonstrate atomic memory for correlated photon states, stationary pulses of light, and shaping of quantum pulses via atomic memory.
• In the first realization of a two-node quantum network, generation and storage of single-photon pulses in two remote ensembles of atoms connected via a single photon was demonstrated.
• A method involving the use of fixed, minimal physical resources was proposed to achieve generation and nested purification of quantum entanglement for quantum communication over arbitrarily long distances. In one embodiment of this method, the fixed, minimal resources are solid-state single-photon emitters, each having two internal degrees of freedom formed by an electron spin and a nuclear spin. These resources would be used to build intermediate nodes in a quantum channel. It was shown that the fixed, minimal physical resources should suffice to correct arbitrary errors, making a quantumbased communication protocol robust to all realistic sources of decoherence. Recently, a node that utilized nitrogenvacancy centers in a room-temperature diamond lattice was demonstrated.

This work was done by Mikhail Lukin, Alexander Zibrov, Ehud Altman, Vlatko Balic, Gurudev Dutt, Dimitry Petrov, Anatoli Polkovnikov, Andre Sorensen, Casper van der Wal, Philip Walther, Daw-wei Wang, Tomasso Calarco, Ana Maria Rey, Axel Andr, Michal Bajscy, Darrick Chang, Lilian Childress, Matthew Eisaman, Mohammad Hafezi, Michael Hohensee, Jiang Liang, Aryesh Mukherjee, Alex Nemiroski, Jacob Taylor, Emre Togan, Saijun Wu, Florent Massou dit Labaquere, and Sidharth Shenai of Harvard College; Philip Hemmer and Mughees Khan of Texas A&M University; Peter Zoller of the University of Innsbruck; Ronald Walsworth of the Smithsonian Astrophysical Observatory; and Charles Marcus of Harvard University for the Naval Research Laboratory.

This Brief includes a Technical Support Package (TSP).

Research on Quantum Communication Repeaters (reference NRL-0017) is currently available for download from the TSP library.

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