Volume 5 Issue 4, April 2009

Volume 5 Issue 4

Topological insulators are band insulators with large spin–orbit coupling, in which surface states give rise to gap-traversing modes that are robust against scattering. Theory now predicts that screw dislocations and other types of defects can give rise to one-dimensional topologically protected states in such systems. Article p298 Cover design by David Shand

Editorials

  • Editorial |

    Research could progress as never before as scientists embrace the ever-growing possibilities for collaboration via the web.

  • Editorial |

    It was all going so well — but then Obama's science appointments were blocked.

Commentary

  • Commentary |

    Online tools for collaboration and sharing information have changed the routine of scientists. But the revolution that will turn scientific information from a collection of files into an active system has just begun.

    • Michael Nielsen

Thesis

Books and Arts

Research Highlights

News and Views

  • News & Views |

    A counterexample to the 'additivity question', the most celebrated open problem in the mathematical theory of quantum information, casts doubt on the possibility of finding a simple expression for the information capacity of a quantum channel.

    • Peter W. Shor
  • News & Views |

    Strong coupling between a mechanical oscillator and the spin of an electron could enable cooling of the oscillator to its quantum ground state and measurement of the zero-point fluctuations.

    • Jörg Wrachtrup
  • News & Views |

    Magnetic materials provide a new context for observing magnetic monopoles. Numerical simulations now establish an experimentally measurable signature of their dynamics — one that has in fact already been seen in a spin-ice compound.

    • Roderich Moessner
    •  & Peter Schiffer
  • News & Views |

    Although the bunching of photons emitted from an incoherent source is well known, the nanosecond response times of conventional photon-counting detectors have prevented it from being observed directly. Using the ultrafast two-photon absorption characteristics of a semiconductor detector, such effects can now be studied at femtosecond timescales.

    • Giuliano Scarcelli
  • News & Views |

    The combination of quantum-state selection and shaped femtosecond laser pulses provides a tool for creating samples of isolated molecules with precisely defined and controlled spatial orientation.

    • Jonathan G. Underwood

Letters

  • Letter |

    The additivity conjecture of quantum information theory implies that entanglement cannot, even in principle, help to funnel more classical information through a quantum-communication channel. A counterexample shows that this conjecture is false.

    • M. B. Hastings
  • Letter |

    Magnetic monopoles have for a long time eluded detection by experiment. Theory now identifies a signature of monopole dynamics that is measurable experimentally, and that has already been seen in magnetic relaxation measurements in a spin-ice material.

    • L. D. C. Jaubert
    •  & P. C. W. Holdsworth
  • Letter |

    The spin state of electrons trapped in a quantum dot only lasts a few microseconds. Before this information is lost, it is useful to controllably rotate the spin as many times as possible. Laser pulses can now rotate electron spins in an ensemble of quantum dots in just a few picoseconds.

    • A. Greilich
    • , Sophia E. Economou
    • , S. Spatzek
    • , D. R. Yakovlev
    • , D. Reuter
    • , A. D. Wieck
    • , T. L. Reinecke
    •  & M. Bayer
  • Letter |

    Although the bunching of photons emitted from an incoherent source is well known, this has only ever been measured down to a temporal resolution of nanoseconds. This has now been improved by many orders of magnitude to the level of femtoseconds, with the elegantly simple use of a GaAs two-photon detector.

    • F. Boitier
    • , A. Godard
    • , E. Rosencher
    •  & C. Fabre
  • Letter |

    The broadening of a wave-packet can be suppressed as it propagates through a periodic potential. The first-order effect of this so-called dynamic localization has been seen in many different systems. Higher-order effects are now seen for the first time in an optical pulse guided along curved photonic lattices.

    • Alexander Szameit
    • , Ivan L. Garanovich
    • , Matthias Heinrich
    • , Andrey A. Sukhorukov
    • , Felix Dreisow
    • , Thomas Pertsch
    • , Stefan Nolte
    • , Andreas Tünnermann
    •  & Yuri S. Kivshar
  • Letter |

    A proposed device—an optical analogue of the superconducting Josephson interferometer—might enable detailed studies of the role that dissipation has in strongly correlated quantum-optical systems.

    • Dario Gerace
    • , Hakan E. Türeci
    • , Atac Imamoglu
    • , Vittorio Giovannetti
    •  & Rosario Fazio
  • Letter |

    High-speed spectroscopy confirms predictions of the emission of terahertz radiation when a laser-induced acoustic wave passes across the interface between two piezoelectric materials.

    • Michael R. Armstrong
    • , Evan J. Reed
    • , Ki-Yong Kim
    • , James H. Glownia
    • , William M. Howard
    • , Edwin L. Piner
    •  & John C. Roberts
  • Letter |

    A technique that produces significant alignment of molecules in a beam should aid a wide range of experiments geared towards understanding and controlling molecular processes in the gas phase.

    • Omair Ghafur
    • , Arnaud Rouzée
    • , Arjan Gijsbertsen
    • , Wing Kiu Siu
    • , Steven Stolte
    •  & Marc J. J. Vrakking

Articles

  • Article |

    Topological insulators are band insulators in which spin–orbit coupling takes the role of the applied magnetic field in the integer quantum Hall effect. Theory now predicts that dislocations in such systems can give rise to one-dimensional topologically protected states, resembling helical modes at the edge of a two-dimensional quantum spin Hall insulator.

    • Ying Ran
    • , Yi Zhang
    •  & Ashvin Vishwanath
  • Article |

    The description of valence electrons in terms of non-local states that extend throughout a material presents problems for describing their contribution to ferroelectric polarization behaviour, which is inherently local. A new first-principles approach that treats electric displacement as a fundamental variable could provide a solution.

    • Massimiliano Stengel
    • , Nicola A. Spaldin
    •  & David Vanderbilt