A technique for increasing the time that quantum information is stored in glass fiber-coupled atoms could yield a global optical fiber-based quantum communication network, researchers in Austria have found. There are several approaches for performing quantum mechanical operations and exchanging quantum information between light and matter-based memories, but for many of these systems it is challenging to efficiently store and retrieve the information. Although researchers have demonstrated that atoms can be controlled and efficiently coupled to glass fibers, the suitability of the atoms for storing quantum information and for long-distance quantum communication has remained an open question. Now, researchers at the Vienna University of Technology (TU Vienna) have demonstrated experimentally that atoms quantum mechanically coupled to glass fibers are capable of storing quantum information long enough so that they could be used for entangling atoms hundreds of kilometers apart — a fundamental building block for global networks based on optical fibers. Scientists at TU Vienna have demonstrated experimentally that atoms quantum mechanically coupled to glass fibers are capable of storing quantum information long enough so that they could be used for entangling atoms hundreds of kilometers apart. Their findings could yield a global optical fiber-based quantum communication network. Courtesy of TU Vienna. “In our experiment, we connect two different quantum physical systems,” said Arno Rauschenbeutel of TU Vienna’s Vienna Center for Quantum Science and Technology and Institute of Atomic and Subatomic Physics. “One the one hand, we use fiber-guided light, which is perfect for sending quantum information from A to B, and, on the other hand, we rely on atoms, which are ideal for storing this information.” By trapping atoms at a distance of about 200 nm from a 500-nm-diameter glass fiber, a strong interaction between light and atoms can be implemented. The two systems are then able to exchange quantum information — a process that forms a basis for possible future technologies such as quantum cryptography or quantum teleportation. “Our setup is directly connected to a standard optical glass fiber that is nowadays routinely used for the transmission of data,” Rauschenbeutel said. “It will therefore be easy to integrate our quantum glass fiber cable into existing fiber communication networks.” The investigators also managed to increase the period of time that the atoms can stay coupled to glass fiber. Researchers have observed that, after some time, quantum information stored in the atoms is lost as it leaks into the environment — an effect called decoherence. “Using some tricks, we were able to extend the coherence time of the atoms to several milliseconds, in spite of their small distance to the fiber surface,” he said. As light is the carrier of quantum information, its speed in glass fiber sets the upper limit for the distance that can be overcome via entangled atoms. Even in standard glass fiber-based telecommunication, signal weakens with the length of the fiber. To overcome this, repeater stations are inserted into the network to amplify the weakening optical signal. For quantum networks, special “quantum repeaters” would have to be created to link several shorter sections into one long quantum connection. Rauschenbeutel believes that his technique could serve as a basis for developing such future quantum networks. “By using our combined nanofiber-atom-system for setting up an optical quantum network including quantum repeaters, one might transmit quantum information and teleport quantum states around the world,” he said. The research appeared in Physical Review Letters (doi: 10.1103/PhysRevLett.110.243603). For more information, visit: www.tuwien.ac.at/en