Volume 8 Issue 9, September 2012

Volume 8 Issue 9

Magnetic vortices confined to thin films gyrate with dynamics that are determined by the vortex-core polarity, which switches when the gyration is fast enough. Fine-tuning these core-reversal oscillations reveals rich nonlinear behaviour, including commensurate and chaotic states. Article p682 COVER IMAGE: JOO-VON KIM AND ANTONIO RUOTOLO COVER DESIGN: ALLEN BEATTIE

Editorials

Thesis

Research Highlights

News and Views

  • News & Views |

    Technologies aimed at single-molecule resolution of non-equilibrium systems increasingly require sophisticated new ways of thinking about thermodynamics. An elegant extension to standard fluctuation theory grants access to the kinetic intermediate states of these systems — as DNA-pulling experiments now demonstrate.

    • Jan Liphardt
  • News & Views |

    In most electrical conductors, we expect charge and heat to be transported in the same direction. However, in certain two-dimensional electron systems, fractional quantum Hall states can cause charge and heat to flow in opposite directions.

    • Stefan Heun
  • News & Views |

    Hybrid traps for laser-cooled ions and neutral atoms make excellent cold-chemistry laboratories. Experiments now show that engineering quantum states can provide additional control for accessing and manipulating chemical reaction rates.

    • Paul S. Julienne
  • News & Views |

    In two-dimensional systems, superfluidity occurs in the absence of the long-range order associated with Bose–Einstein condensates. This phenomenon is illustrated in the direct observation of superfluidity in a 2D atomic Bose gas.

    • Gretchen K. Campbell

Letters

  • Letter |

    Two-dimensional Bose fluids—such as liquid-helium films, or confined ultracold atoms—cannot form a condensate, but become superfluid instead. Frictionless flow, proving superfluid behaviour, has now been observed in an ultracold two-dimensional Bose gas that is stirred with a laser beam.

    • Rémi Desbuquois
    • , Lauriane Chomaz
    • , Tarik Yefsah
    • , Julian Léonard
    • , Jérôme Beugnon
    • , Christof Weitenberg
    •  & Jean Dalibard
  • Letter |

    Chemical reactions between a single trapped ion and a condensate of ultracold neutral atoms are investigated by controlling the quantum states of both ion and atoms—revealing the effect of the hyperfine interaction on the reaction dynamics.

    • Lothar Ratschbacher
    • , Christoph Zipkes
    • , Carlo Sias
    •  & Michael Köhl
  • Letter |

    In metals, the Coulomb potential of charged impurities is strongly screened, but in graphene, the potential charge of a few-atom cluster of cobalt can extend up to 10 nm. By measuring differences in the way electron-like and hole-like Dirac fermions are scattered from this potential, the intrinsic dielectric constant of graphene can be determined.

    • Yang Wang
    • , Victor W. Brar
    • , Andrey V. Shytov
    • , Qiong Wu
    • , William Regan
    • , Hsin-Zon Tsai
    • , Alex Zettl
    • , Leonid S. Levitov
    •  & Michael F. Crommie
  • Letter |

    In systems of oscillators, phase-locking behaviour can, in theory, coexist with incoherent dynamics—invoking the fabled chimera state. Now, experimental realization of a coupled-map lattice reveals dynamical states displaying coexisting spatial domains of coherence and incoherence.

    • Aaron M. Hagerstrom
    • , Thomas E. Murphy
    • , Rajarshi Roy
    • , Philipp Hövel
    • , Iryna Omelchenko
    •  & Eckehard Schöll
  • Letter |

    Chimera states describing the stable coexistence of synchronous and incoherent dynamics have so far only been realized numerically. An experimental demonstration of these states in a network of discrete chemical oscillators reveals behaviour that differs from that predicted by existing phase-oscillator models.

    • Mark R. Tinsley
    • , Simbarashe Nkomo
    •  & Kenneth Showalter

Articles

  • Article |

    Quantum discord is the total non-classical correlation between two systems. This includes, but is not limited to, entanglement. Photonic experiments now demonstrate that separable states with non-zero quantum discord are a useful resource for quantum information processing and can even outperform entangled states.

    • Borivoje Dakić
    • , Yannick Ole Lipp
    • , Xiaosong Ma
    • , Martin Ringbauer
    • , Sebastian Kropatschek
    • , Stefanie Barz
    • , Tomasz Paterek
    • , Vlatko Vedral
    • , Anton Zeilinger
    • , Časlav Brukner
    •  & Philip Walther
  • Article |

    Entanglement is not the only type of quantum correlation. Quantum discord is a broader measure of such non-classical interactions. An experimental investigation now shows how quantum discord can be consumed to encode information, even in the absence of entanglement.

    • Mile Gu
    • , Helen M. Chrzanowski
    • , Syed M. Assad
    • , Thomas Symul
    • , Kavan Modi
    • , Timothy C. Ralph
    • , Vlatko Vedral
    •  & Ping Koy Lam
  • Article |

    In most electrical conductors, heat is transported by charge carriers and so both usually flow in the same direction; but in two-dimensional electron systems subject to strong magnetic fields, certain fractional quantum Hall states can cause charge and heat to flow in opposite directions.

    • Vivek Venkatachalam
    • , Sean Hart
    • , Loren Pfeiffer
    • , Ken West
    •  & Amir Yacoby
  • Article |

    Magnetic vortices confined to thin films gyrate with a dynamics determined by the vortex–core polarity, which switches when the gyration is fast enough. Fine-tuning these core-reversal oscillations reveals rich nonlinear behaviour, including commensurate and chaotic states.

    • Sebastien Petit-Watelot
    • , Joo-Von Kim
    • , Antonio Ruotolo
    • , Ruben M. Otxoa
    • , Karim Bouzehouane
    • , Julie Grollier
    • , Arne Vansteenkiste
    • , Ben Van de Wiele
    • , Vincent Cros
    •  & Thibaut Devolder
  • Article |

    Short-lived kinetic states between equilibria are difficult to access experimentally, despite being crucial in many dynamical processes. Single-molecule experiments demonstrate that an extended fluctuation relation allows extraction of the free energies of these metastable states under non-equilibrium conditions.

    • Anna Alemany
    • , Alessandro Mossa
    • , Ivan Junier
    •  & Felix Ritort