Physics articles within Nature

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  • Letter |

    Quantum entanglement is widely used in fundamental tests of quantum mechanics and applications such as quantum cryptography. Previous experiments have demonstrated entanglement of optical photons with trapped atoms, ions and atomic ensembles. These authors realize quantum entanglement between the polarization of a single optical photon and a solid-state qubit associated with a single electronic spin. This may provide a key building block for the solid-state realization of quantum optical networks.

    • E. Togan
    • , Y. Chu
    •  & M. D. Lukin

  • Letter |

    Attosecond technology (1 as = 10−18 S) promises the tools needed to directly probe electron motion in real time. These authors report attosecond pump–probe measurements that track the movement of valence electrons in krypton ions. This first proof-of-principle demonstration uses a simple system, but the expectation is that attosecond transient absorption spectroscopy will ultimately also reveal the elementary electron motions that underlie the properties of molecules and solid-state materials.

    • Eleftherios Goulielmakis
    • , Zhi-Heng Loh
    •  & Ferenc Krausz

  • Letter |

    Metamaterials have the counterintuitive optical property of negative refraction index. They have a wide range of possible applications, including 'invisibility cloaks' and perfect lenses, but their performance is severely limited by absorption losses. These authors have incorporated an optical gain medium within a metamaterial as a way to compensate the intrinsic loss, and show that optical pumping leads to a significantly improved negative refraction index and figure of merit within the 722–738-nm visible wavelength range.

    • Shumin Xiao
    • , Vladimir P. Drachev
    •  & Vladimir M. Shalaev

  • News & Views |

    Attosecond spectroscopy has been used to track the real-time motion of electrons in a krypton ion, and to probe the entanglement between an electron removed from the atom and the ion left behind.

    • Olga Smirnova

  • News |

    A storm is brewing round the scientists in line to win the Nobel prize for predicting the elusive particle.

    • Zeeya Merali

  • Article |

    The quantum Hall effect takes place in a two-dimensional electron gas under a strong magnetic field and involves current flow along the edges of the sample. In the fractional regime, counter-propagating modes that carry energy but not charge — the so-called neutral modes — have been predicted but never observed. These authors report the first direct observation of these elusive modes.

    • Aveek Bid
    • , N. Ofek
    •  & D. Mahalu

  • Letter |

    New methods are emerging that aim to image chemical reactions as they occur using X-ray diffraction, electron diffraction or laser-induced recollision, but spectral selection cannot be used to monitor the reacting molecules for these methods. These authors show that this apparent limitation offers opportunities for recollision-based high-harmonic spectroscopy, in which unexcited molecules can act as local oscillators against which structural and electronic dynamics is observed on an attosecond timescale.

    • H. J. Wörner
    • , J. B. Bertrand
    •  & D. M. Villeneuve

  • Letter |

    Fluctuations arising from Heisenberg's uncertainty principle enable quantum systems to exhibit phase transitions even at zero temperature. For example, a superfluid-to-insulator transition has been observed for weakly interacting bosonic atomic gases. Here the authors report a novel type of quantum phase transition in a strongly interacting, one-dimensional quantum gas of bosonic caesium atoms. The results open up the experimental study of ultracold gases in a new regime.

    • Elmar Haller
    • , Russell Hart
    •  & Hanns-Christoph Nägerl

  • Letter |

    Non-classical states of light, such as entangled photon states, form an essential quantum resource. Entangled photon pairs can be created by spontaneous parametric down-conversion of laser light, but so far it has not been possible to produce photon triplets in this way. These authors report the generation of quantum-correlated photon triplets by cascaded down-conversion of a single pump photon. This should find widespread use in optical quantum technologies.

    • Hannes Hübel
    • , Deny R. Hamel
    •  & Thomas Jennewein

  • Review Article |

    For 350 years after Galileo's discoveries, ground-based telescopes and theoretical modelling furnished everything known about the Sun's planetary retinue. Over the past five decades, data from spacecraft sent to all the planets and some of their satellites have shown the diversity of Solar System bodies. Many planets and satellites have changed substantially since their birth, and violent events punctuate their histories.

    • Joseph A. Burns

  • News & Views |

    Noise is usually viewed as the bane of measurements. But a neat experiment has confirmed a long-standing prediction for an exotic electronic state of matter through the increase of noise in charge transmission.

    • Chetan Nayak

  • Letter |

    Hitherto, 21-cm emission has been detected in galaxies only to redshift 0.24, although it is possible to measure the aggregate emission from many more distant, unresolved sources in the 'cosmic web'. Here the authors report a three-dimensional 21-cm intensity field at redshift 0.53–1.12. They co-add neutral-hydrogen emission from the volumes surrounding about 10,000 galaxies to detect the aggregate 21-cm glow at a significance of approximately four standard deviations.

    • Tzu-Ching Chang
    • , Ue-Li Pen
    •  & Jeffrey B. Peterson

  • News Feature |

    NASA and Germany have spent 15 years and billions of dollars on SOFIA, an airborne telescope that is about to produce its first results. Eric Hand asks whether the science will justify the cost.

    • Eric Hand

  • Letter |

    Topological surface states are a class of electronic states that might be of interest in quantum computing or spintronic applications. They are predicted to be robust against imperfections, but so far there has been no evidence that these states do transmit through naturally occurring surface defects. Here, scanning tunnelling microscopy has been used to show that topological surface states of antimony can be transmitted through naturally occurring barriers that block non-topological surface states of common metals.

    • Jungpil Seo
    • , Pedram Roushan
    •  & Ali Yazdani

  • Letter |

    Circumstellar disks are an essential ingredient of the formation of low-mass stars, but it is unclear whether they are also required for the formation of stars more massive than about 10 solar masses. Clear observational evidence is needed, for example the detection of dusty disks around massive young stellar objects. Here, near-infrared interferometric observations are reported that spatially resolve the distribution of hot material around a high-mass young stellar object.

    • Stefan Kraus
    • , Karl-Heinz Hofmann
    •  & Leonardo Testi

  • News & Views |

    The Universe is expanding. And the expansion seems to be speeding up. To account for that acceleration, a mysterious factor, 'dark energy', is often invoked. A contrary opinion — that this factor isn't at all mysterious — is here given voice, along with counter-arguments against that view.

    • Eugenio Bianchi
    • , Carlo Rovelli
    •  & Rocky Kolb

  • News & Views |

    According to theory, electrons on the surface of a topological insulator are not allowed to make U-turns. This notion, and some of its main consequences, has now been tested experimentally.

    • Marcel Franz

  • News Feature |

    A new class of materials is poised to take condensed-matter physics by storm. Geoff Brumfiel looks at what is making topological insulators all the rage.

    • Geoff Brumfiel

  • Letter |

    Quantum information science requires a source of entangled photon pairs, but existing sources suffer from a low intrinsic efficiency or poor extraction efficiency. Collecting emitted photons from quantum dots can be improved by coupling the dots to an optical cavity, but this is not easy for entangled photon pairs. Now, a suitable optical cavity has been made in the form of a 'photonic' molecule — two identical, connecting microcavities that are deterministically coupled to the optically active modes of a pre-selected quantum dot.

    • Adrien Dousse
    • , Jan Suffczyński
    •  & Pascale Senellart

  • Letter |

    Here, a technically challenging spectroscopic experiment is described: the measurement of the muonic Lamb shift. The results lead to a new determination of the charge radius of the proton. The new value is 5.0 standard deviations smaller than the previous world average, a large discrepancy that remains unexplained. Possible implications of the new finding are that the value of the Rydberg constant will need to be revised, or that the validity of quantum electrodynamics theory is called into question.

    • Randolf Pohl
    • , Aldo Antognini
    •  & Franz Kottmann

  • News & Views |

    A measurement of the size of the proton, obtained using spectroscopy of an exotic atomic system, yields a result of unprecedented accuracy — but in disagreement with values obtained by previous methods.

    • Jeff Flowers

  • Article |

    With the start-up of the first X-ray free-electron laser, a new era has begun in dynamical studies of atoms. Here the facility is used to study the fundamental nature of the electronic response in free neon atoms. During a single X-ray pulse, they sequentially eject all their ten electrons to produce fully stripped neon. The authors explain this electron-stripping in a straightforward model, auguring favourably for further studies of interactions of X-rays with more complex systems.

    • L. Young
    • , E. P. Kanter
    •  & M. Messerschmidt

  • Letter |

    Light–matter interactions in semiconductors hold great promise for numerous applications, but as device size is reduced such interactions typically weaken, potentially posing problems for applications at the nanoscale. Here the authors circumvent these limitations by producing colloidal particles with metallic cores and semiconducting shells, in which coupling of the plasmons in the metal to the excitons in the semiconductor is engineered to enhance light–matter interactions in the particle.

    • Jiatao Zhang
    • , Yun Tang
    •  & Min Ouyang

  • Letter |

    When electrons or photons are used to detect the motion of a mechanical resonator, they exert tiny forces on the resonator, subtly changing its motion. Here, through analysis of electrical noise measurements, the authors report a striking example of such back-action where electrons tunnelling through a semiconductor quantum device cause vibrations of the host crystal, which is massive compared with the electrons — an effect comparable to a flea causing metre-scale vibrations in Mount Everest.

    • Joel Stettenheim
    • , Madhu Thalakulam
    •  & A. J. Rimberg

  • News & Views |

    A simple model highlights the pros and cons of chasing — and escaping — in groups. It shows that, for a given number of prey animals, an optimal number of predators exists that maximizes the success of the catch.

    • Tamás Vicsek

  • News & Views |

    The world's first kiloelectronvolt X-ray laser produces such a high flux of photons that atoms can be 'cored'. In other words, the light source can knock out both the electrons of an atom's innermost shell.

    • Justin Wark

  • Letter |

    A quantum memory would enable storage and retrieval of a quantum state of light without corrupting the information it carries. Previous devices have had low efficiencies of less than 17 per cent, and used weak quantum states with an average photon number of around one. Now a solid-state quantum memory is described with an efficiency of up to 69 per cent, which performs better than a classical device for bright states of up to 500 photons.

    • Morgan P. Hedges
    • , Jevon J. Longdell
    •  & Matthew J. Sellars

  • Letter |

    If the orbital velocity of an extrasolar planet could be determined, the masses of both the planet and its host star could be calculated using Newton's law of gravity. Here, high-dispersion ground-based spectroscopy of a transit of the extrasolar planet HD 209458b is reported. This allowed the radial component of the planet's orbital velocity to be calculated, and thus the masses of star and planet. Moreover, a strong wind flowing from the irradiated dayside to the non-irradiated nightside of the planet is suggested.

    • Ignas A. G. Snellen
    • , Remco J. de Kok
    •  & Simon Albrecht

  • News & Views |

    The masses of exoplanets have so far been inferred from the tiny gravitational pull they exert on the host stars. It is now possible to measure them from shifts in spectral lines arising from the planets' atmospheres.

    • Mercedes López-Morales

  • Books & Arts |

    Robert P. Crease is fascinated by a biography of quantum physicist Hugh Everett III, the difficult man behind one of the most logical and bizarre ideas in the history of human thought.

    • Robert P. Crease

  • Letter |

    Network theory has become pervasive in all sectors of biology, from biochemical signalling to human societies, but identification of relevant functional communities has been impaired by many nodes belonging to several overlapping groups at once, and by hierarchical structures. These authors offer a radically different viewpoint, focusing on links rather than nodes, which allows them to demonstrate that overlapping communities and network hierarchies are two faces of the same issue.

    • Yong-Yeol Ahn
    • , James P. Bagrow
    •  & Sune Lehmann

  • Letter |

    Over the past few decades, two techniques in particular have opened up new avenues for probing molecular processes: ultrafast spectroscopy and single-molecule detection. The two approaches have now been combined, enabling not only the observation but also the manipulation of vibrational wave-packet interference at ambient conditions. The technique could help to unravel details of molecular function and dynamics in systems as diverse as light-harvesting complexes, photoactive proteins and conjugated polymers.

    • Daan Brinks
    • , Fernando D. Stefani
    •  & Niek F. van Hulst

  • Letter |

    Skyrmions are stable topological textures with particle-like properties — a mathematical concept that was originally used to describe nuclear particles but has since turned up at all scales. Last year, the presence of skyrmions in the magnetic compounds MnSi and Fe1−xCoxSi was confirmed with neutron-scattering experiments. Here, real-space images are presented of a two-dimensional skyrmion lattice in a thin film of the latter compound. The observed nanometre-scale spin topology might reveal new magneto-transport effects.

    • X. Z. Yu
    • , Y. Onose
    •  & Y. Tokura

  • Editorial |

    Celebrating the treasures of topological twists.

  • Books & Arts |

    Frank Close enjoys a journalistic account of the sociology and politics of the search for the elusive particle named after physicist Peter Higgs, but cautions that the idea has deeper roots than its name implies.

    • Frank Close

  • News & Views |

    Skyrmions are a special type of particle that has long been predicted to exist in many fields of physics. Direct images of these structures have now been made in a magnetic material.

    • Christian Pfleiderer
    •  & Achim Rosch

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