Volume 7 Issue 3, March 2011

Volume 7 Issue 3

Quantum dots are usually assumed to interact with light as atom-like point sources. A study of the behaviour of quantum dots placed close to a metal mirror suggests this isn't the case. Rather, a quantum dot's finite size causes the strength of its interaction with light to oscillate with its distance from a nearby mirror. Letter p215 Cover design by David Shand

Editorials

  • Editorial |

    The first tentative steps towards a comprehensive policy on scientific integrity, to guide scientists and politicians, are being taken in the US. Progress is slow, but should be encouraged.

  • Editorial |

    It's time to give serious consideration to the notion of job-sharing in science.

Thesis

Books and Arts

Research Highlights

News and Views

  • News & Views |

    Rotating black holes twist photons emitted nearby, a peculiar effect in general relativity that is now demonstrated by numerical experiments. This twisted light and its orbital angular momentum could reveal the physics of black holes in more detail than deemed possible before.

    • Martin Bojowald
  • News & Views |

    A thermal Casimir force — an attraction between two metal surfaces caused by thermal, rather than quantum, fluctuations in the electromagnetic field — is now identified experimentally, with implications for our understanding of electrodynamics.

    • Kimball Milton
  • News & Views |

    Every metal has a Fermi surface, which gives rise to quantum oscillations in a magnetic field. But the nature of the Fermi surface in cuprate superconductors is a profound mystery that scientists are only starting to unravel.

    • Stephen R. Julian
    •  & Michael R. Norman
  • News & Views |

    Elementary excitations in certain rare-earth titanates emulate the behaviour of a gas of magnetic point charges. Such magnetic monopoles should respond to a magnetic-field pulse exactly as a partially ionized plasma does to an electric-field pulse. This analogy has now been verified.

    • Michael Bonitz

Letters

  • Letter |

    General relativity predicts that some black holes rotate. It is now shown that these Kerr black holes imprint their signature on light emitting from nearby sources: twisting it in a way that might be detected by modern telescopes.

    • Fabrizio Tamburini
    • , Bo Thidé
    • , Gabriel Molina-Terriza
    •  & Gabriele Anzolin
  • Letter |

    The Kondo effect describes electrons scattering off a magnetic impurity, which affects the resistivity of a metal at low temperatures. In the case of buried iron or cobalt atoms, the correlations are longer ranged than studies of adatoms have shown.

    • Henning Prüser
    • , Martin Wenderoth
    • , Piet E. Dargel
    • , Alexander Weismann
    • , Robert Peters
    • , Thomas Pruschke
    •  & Rainer G. Ulbrich
  • Letter |

    Instead of the usual chemical doping or applied pressure methods for controlling quantum phase transitions, it’s now possible to break chemical bonds to tune into a ferromagnetic quantum critical point.

    • Shuang Jia
    • , Pawina Jiramongkolchai
    • , M. R. Suchomel
    • , B. H. Toby
    • , J. G. Checkelsky
    • , N. P. Ong
    •  & R. J. Cava
  • Letter |

    A tour-de-force study finds that as the pressure of lithium is increased to 50 GPa, its melting point drops to 190 K—the lowest yet observed of any elemental metal. The results suggest lithium could be a promising candidate for exploring exotic states of matter similar to that predicted for metallic hydrogen.

    • Christophe L. Guillaume
    • , Eugene Gregoryanz
    • , Olga Degtyareva
    • , Malcolm I. McMahon
    • , Michael Hanfland
    • , Shaun Evans
    • , Malcolm Guthrie
    • , Stanislav V. Sinogeikin
    •  & H-K. Mao
  • Letter |

    Light-emitting quantum dots are usually assumed to behave as perfect point-source emitters. It is now found that this assumption breaks down when quantum dots are placed near structures that support nanoscale optical modes — information that could be useful in building better nanophotonic devices.

    • Mads Lykke Andersen
    • , Søren Stobbe
    • , Anders Søndberg Sørensen
    •  & Peter Lodahl
  • Letter |

    A demonstration of the use of laser-driven plasma accelerators to generate electron beams having sharp temporal features of durations approaching 1 femtosecond, and currents of 3–4 kiloamperes, improves the outlook for using these devices in the development of compact free-electron lasers

    • O. Lundh
    • , J. Lim
    • , C. Rechatin
    • , L. Ammoura
    • , A. Ben-Ismaïl
    • , X. Davoine
    • , G. Gallot
    • , J-P. Goddet
    • , E. Lefebvre
    • , V. Malka
    •  & J. Faure

Articles

  • Article |

    Optical control over electron spins embedded in semiconductor structures is an efficient way of manipulating quantum information. But a fully fledged quantum information processor will require control over two-spin states. This has now been demonstrated, including the implementation of ‘ultrafast’ two-qubit gate operations that take less than a nanosecond.

    • Danny Kim
    • , Samuel G. Carter
    • , Alex Greilich
    • , Allan S. Bracker
    •  & Daniel Gammon
  • Article |

    A thermal Casimir force—an attraction between two metal surfaces caused by thermal, rather than quantum, fluctuations in the electromagnetic field—has now been identified experimentally between a flat and a spherical gold plate.

    • A. O. Sushkov
    • , W. J. Kim
    • , D. A. R. Dalvit
    •  & S. K. Lamoreaux
  • Article |

    Disorder leads to localization of electrons at low temperatures, changing metals to insulators. In a superconductor the electrons are paired up, and scanning tunnelling microscopy shows that the pairs localize together rather than breaking up and forming localized single electrons in the insulating state.

    • Benjamin Sacépé
    • , Thomas Dubouchet
    • , Claude Chapelier
    • , Marc Sanquer
    • , Maoz Ovadia
    • , Dan Shahar
    • , Mikhail Feigel’man
    •  & Lev Ioffe
  • Article |

    The effects of disorder on the electrical characteristics of graphene are found to change drastically in a magnetic field. At zero field, disorder simply causes charge scattering. But at high fields it induces the formation of a network of quantum dots.

    • Suyong Jung
    • , Gregory M. Rutter
    • , Nikolai N. Klimov
    • , David B. Newell
    • , Irene Calizo
    • , Angela R. Hight-Walker
    • , Nikolai B. Zhitenev
    •  & Joseph A. Stroscio
  • Article |

    Magnetic monopoles have recently been discovered in so-called spin-ice materials. The measurement of magnetic current in a spin-ice crystal now demonstrates the macroscopic consequences of these free, magnetically charged particles, and establishes a perfect equivalence between the bulk electrical properties of a conducting fluid and the bulk magnetic properties of spin ice in the magnetic-monopole regime.

    • S. R. Giblin
    • , S. T. Bramwell
    • , P. C. W. Holdsworth
    • , D. Prabhakaran
    •  & I. Terry
  • Article |

    Birefringent particles manipulated with an optical torque wrench exhibit strongly nonlinear, ‘excitable’ behaviour similar to that governing the firing of neurons. This technique could be used to detect small perturbations in the local environment of such a particle.

    • Francesco Pedaci
    • , Zhuangxiong Huang
    • , Maarten van Oene
    • , Stephane Barland
    •  & Nynke H. Dekker
  • Article |

    The nature of the percolation transition—how links add to a system until it is extensively connected—crucially underlies the structure and function of virtually all growing complex networks. Percolation transitions have long been thought to be continuous, but recent numerical work suggests that certain percolating systems exhibit discontinuous phase transitions. This study explains the key microscopic mechanisms underlying such ‘explosive percolation’.

    • Jan Nagler
    • , Anna Levina
    •  & Marc Timme

Erratum