Volume 6 Issue 11, November 2010

Volume 6 Issue 11

The spreading of information, ideas or diseases can be conveniently modelled in the context of complex networks. An analysis now reveals that the most efficient spreaders are not always necessarily the most connected agents in a network. Instead, the position of an agent relative to the hierarchical topological organization of the network might be as important as its connectivity. Letter p888 Cover design by David Shand

Editorial

  • Editorial |

    Achievement of the United Nations' Millenium Development Goals is by no means guaranteed, but there is heartening progress in the promotion of science for development.

Correspondence

Commentaries

  • Commentary |

    Fifty years ago, Abdus Salam envisaged a 'world centre' for theorists. Now the institute that he founded is adapting to a changing world and to changing ways of doing science.

    • Gordon Fraser
  • Commentary |

    A school on computational materials science that drew expert teachers and talented participants marks a new approach to the development of research in Africa.

    • Nithaya Chetty
    • , Richard M. Martin
    •  & Sandro Scandolo

Thesis

Books and Arts

Research Highlights

News and Views

  • News & Views |

    The quantum kagome lattice is a fundamental but experimentally elusive frustrated magnet. Neutron spectroscopy now reveals the ground state and elementary excitations of a deformed kagome lattice in which the quantum spins form an exotic pinwheel valence-bond state.

    • Christian Rüegg
  • News & Views |

    Converting data-carrying photons to telecommunication wavelengths enables distribution of quantum information over long distances.

    • Mark Saffman
  • News & Views |

    Measurement-based quantum computation with an Affleck–Kennedy–Lieb–Tasaki state is experimentally realized for the first time.

    • Robert Raussendorf
  • News & Views |

    Quantum mechanics predicts that measurements on spatially separated particles can yield non-local correlations. This is well established but defies intuition about space and time. The concept of 'steering' might help us to understand quantum non-locality better.

    • Nicolas Brunner

Letters

  • Letter |

    Erwin Schrödinger introduced in 1935 the concept of ‘steering’, which generalizes the famed Einstein–Podolsky–Rosen paradox. Steering sits in between quantum entanglement and non-locality — that is, entanglement is necessary for steering, but steering can be achieved, as has now been demonstrated experimentally, with states that cannot violate a Bell inequality (and therefore non-locality).

    • D. J. Saunders
    • , S. J. Jones
    • , H. M. Wiseman
    •  & G. J. Pryde
  • Letter |

    One-way quantum computing requires an entangled multiqubit system. So-called cluster states have been proposed to provide this resource, but they are difficult to generate. An alternative that uses the ground state of a one-dimensional chain of spins is now experimentally realized and used to construct a quantum logic gate.

    • Rainer Kaltenbaek
    • , Jonathan Lavoie
    • , Bei Zeng
    • , Stephen D. Bartlett
    •  & Kevin J. Resch
  • Letter |

    When doped with copper, the topological insulator Bi2Se3 becomes superconducting. But for new physics and applications the search is not for just any superconductor; the material must retain its topological character. And indeed that is the case with doped Bi2Se3.

    • L. Andrew Wray
    • , Su-Yang Xu
    • , Yuqi Xia
    • , Yew San Hor
    • , Dong Qian
    • , Alexei V. Fedorov
    • , Hsin Lin
    • , Arun Bansil
    • , Robert J. Cava
    •  & M. Zahid Hasan
  • Letter |

    Long-lived polariton condensates can propagate well beyond the area of their initial excitation while still maintaining spatial coherence. This enables direct and controllable manipulation of the condensate wavefunction.

    • E. Wertz
    • , L. Ferrier
    • , D. D. Solnyshkov
    • , R. Johne
    • , D. Sanvitto
    • , A. Lemaître
    • , I. Sagnes
    • , R. Grousson
    • , A. V. Kavokin
    • , P. Senellart
    • , G. Malpuech
    •  & J. Bloch
  • Letter |

    Monitoring the photocurrent generated as a laser scans across a graphene field-effect device subjected to low temperature and high magnetic fields enables the spatial distribution of Landau levels across a graphene sheet to be mapped. This in turn allows the relative contribution of bulk and edge states to the macroscopic electrical characteristics of these devices to be determined.

    • G. Nazin
    • , Y. Zhang
    • , L. Zhang
    • , E. Sutter
    •  & P. Sutter
  • Letter |

    A pure spin current has no net charge current and is therefore difficult to detect. A new technique that takes advantage of nonlinear optical effects can measure pure spin currents non-invasively, non-destructively and in real-time.

    • Lalani K. Werake
    •  & Hui Zhao
  • Letter |

    The experimental demonstration of heat currents driving the injection of spins from a ferromagnetic into a non-magnetic metal establishes a new source of pure spin currents. The approach might provide an alternative mechanism for switching processes in memory devices and for other ‘spintronics’ applications.

    • A. Slachter
    • , F. L. Bakker
    • , J-P. Adam
    •  & B. J. van Wees
  • Letter |

    Introducing a phase shift between diffracted and undiffracted light from a sample is one of the oldest techniques for generating phase contrast in optical microscopy. A similar approach should help improve the contrast and clarity of images collected by scanning X-ray microscopy.

    • Christian Holzner
    • , Michael Feser
    • , Stefan Vogt
    • , Benjamin Hornberger
    • , Stephen B. Baines
    •  & Chris Jacobsen
  • Letter |

    Spreading of information, ideas or diseases can be conveniently modelled in the context of complex networks. An analysis now reveals that the most efficient spreaders are not always necessarily the most connected agents in a network. Instead, the position of an agent relative to the hierarchical topological organization of the network might be as important as its connectivity.

    • Maksim Kitsak
    • , Lazaros K. Gallos
    • , Shlomo Havlin
    • , Fredrik Liljeros
    • , Lev Muchnik
    • , H. Eugene Stanley
    •  & Hernán A. Makse

Articles

  • Article |

    Atomic transitions afford a convenient way of storing quantum bits. However, there are few ground-state transitions suitable for use with light at telecommunication wavelengths. Now, researchers show that ensembles of cold rubidium atoms not only make good quantum memories, but can also noiselessly convert the emitted photons into and out of the telecoms band.

    • A. G. Radnaev
    • , Y. O. Dudin
    • , R. Zhao
    • , H. H. Jen
    • , S. D. Jenkins
    • , A. Kuzmich
    •  & T. A. B. Kennedy
  • Article |

    In one-dimensional systems, phase transitions at finite temperature are deemed impossible, because long-range correlations are destroyed by thermal fluctuations. Theoretical work now shows that, nonetheless, a phase transition at finite temperature can occur in a one-dimensional gas of weakly interacting bosons in a random environment

    • I. L. Aleiner
    • , B. L. Altshuler
    •  & G. V. Shlyapnikov
  • Article |

    Quantitative measurements that establish the existence and evolution of quasiparticles across the whole phase diagram of a cuprate superconductor help to distinguish the many theoretical models for high-temperature superconductivity.

    • D. Fournier
    • , G. Levy
    • , Y. Pennec
    • , J. L. McChesney
    • , A. Bostwick
    • , E. Rotenberg
    • , R. Liang
    • , W. N. Hardy
    • , D. A. Bonn
    • , I. S. Elfimov
    •  & A. Damascelli
  • Article |

    Diffraction conventionally limits the length scale on which spins can be optically probed. A new technique that uses doughnut-shaped beams of light to select just one nitrogen-vacancy centre, by suppressing the fluorescence from those around it, enables single-spin detection, imaging and manipulation with nanoscale resolution.

    • P. C. Maurer
    • , J. R. Maze
    • , P. L. Stanwix
    • , L. Jiang
    • , A. V. Gorshkov
    • , A. A. Zibrov
    • , B. Harke
    • , J. S. Hodges
    • , A. S. Zibrov
    • , A. Yacoby
    • , D. Twitchen
    • , S. W. Hell
    • , R. L. Walsworth
    •  & M. D. Lukin
  • Article |

    The energy potentials created by laser light can trap atoms. An analogous effect that traps electrons in solid-state systems is now proposed. The electron traps are created in quantum wells and wires in the presence of quasiparticles composed of two electrons and a hole. The idea could lead to advances in ultrafast optical and new optoelectronic devices.

    • Martin J. A. Schuetz
    • , Michael G. Moore
    •  & Carlo Piermarocchi