Physics

  • Letter |

    When a bubble on a liquid–gas or solid–gas interface ruptures, the general expectation is that the bubble vanishes. Here, it is shown that in many cases interfacial bubbles do not simply vanish when they rupture, but rather create numerous small bubbles via unexpected folding of the ruptured bubble as it retracts. The process may increase the efficiency of rupture-induced aerosol dispersal.

    • James C. Bird
    • , Riëlle de Ruiter
    •  & Howard A. Stone
  • Letter |

    Attosecond (10−18 s) laser pulses make it possible to peer into the inner workings of atoms and molecules on the electronic timescale — phenomena in solids have already been investigated in this way. Here, an attosecond pump–probe experiment is reported that investigates the ionization and dissociation of hydrogen molecules, illustrating that attosecond techniques can also help explore the prompt charge redistribution and charge localization that accompany photoexcitation processes in molecular systems.

    • G. Sansone
    • , F. Kelkensberg
    •  & M. J. J. Vrakking
  • Letter |

    A quantum computer based on optical processes requires a source of entangled photons that can be delivered efficiently on demand. Such a source has now been developed: it involves a compact light-emitting diode with an embedded quantum dot that can be driven electrically to generate entangled photon pairs.

    • C. L. Salter
    • , R. M. Stevenson
    •  & A. J. Shields
  • Letter |

    A network is frustrated when competing interactions between nodes prevent each bond from being satisfied. Frustration in quantum networks can lead to massively entangled ground states, as occurs in exotic materials such as quantum spin liquids and spin glasses. Here, a quantum simulation of a frustrated spin system is described, in which there are three trapped atomic ions whose interactions are controlled using optical forces.

    • K. Kim
    • , M.-S. Chang
    •  & C. Monroe
  • Letter |

    Atomic nuclei have a shell structure that allows for 'magic numbers' of neutrons and protons, analogous to the noble gases in atomic physics. Knowledge of the properties of single-particle states outside nuclear shell closures in exotic nuclei is important for the fundamental understanding of nuclear structure and nucleosynthesis. Here, a nucleon-transfer technique has been used to measure the single-particle states of 133Sn, revealing the highly magic nature of 132Sn.

    • K. L. Jones
    • , A. S. Adekola
    •  & J. S. Thomas
  • Letter |

    Although compound semiconductors like gallium arsenide (GaAs) offer advantages over silicon for photovoltaic and optoelectronic applications, these do not outweigh the costly process of growing large layers of these materials and transferring them to appropriate substrates. However, a new fabrication approach is now demonstrated: films of GaAs and AlGaAs are grown in thick, multilayered assemblies in a single sequence; the individual layers are then released and distributed over foreign substrates by printing.

    • Jongseung Yoon
    • , Sungjin Jo
    •  & John A. Rogers
  • Letter |

    Interactions between microscopic particles are usually described as two-body interactions, although it has been shown that higher-order multi-body interactions could give rise to new quantum phases with intriguing properties. Here, effective six-body interactions are demonstrated in a system of ultracold bosonic atoms in a three-dimensional optical lattice.

    • Sebastian Will
    • , Thorsten Best
    •  & Immanuel Bloch
  • Letter |

    Electromagnetically induced transparency enables the transmission of a laser pulse through an optically dense medium to be manipulated using a control beam. Here this technique is scaled down to a single atom, which acts as a quantum-optical transistor with the ability to coherently control the transmission of light through a cavity. This may lead to novel quantum applications, such as dynamic control of the photon statistics of propagating light fields.

    • Martin Mücke
    • , Eden Figueroa
    •  & Gerhard Rempe
  • Letter |

    Recent progress in solid-state quantum information processing has stimulated the search for amplifiers and frequency converters with quantum-limited performance in the microwave range. Here, a phase-preserving, superconducting parametric amplifier with ultra-low-noise properties has been experimentally realized.

    • N. Bergeal
    • , F. Schackert
    •  & M. H. Devoret
  • Letter |

    Here it is shown, both theoretically and experimentally, that non-local correlations between entangled quantum particles can be used for a new cryptographic application — the generation of certified private random numbers — that is impossible to achieve classically. The results have implications for future device-independent quantum information experiments and for addressing fundamental issues regarding the randomness of quantum theory.

    • S. Pironio
    • , A. Acín
    •  & C. Monroe
  • Article |

    A quantum spin liquid is a hypothetical system of spins (such as those carried by electrons), the orientations of which continue to fluctuate even at absolute zero. Theoretical and experimental evidence for the existence of such states at the microscopic level is elusive, but these authors have modelled correlated electrons arranged on a honeycomb lattice (such as in graphene), and identified the conditions under which a microscopic quantum spin liquid would be realized in two dimensions.

    • Z. Y. Meng
    • , T. C. Lang
    •  & A. Muramatsu
  • Letter |

    X-ray crystallography has become the most common way for structural biologists to obtain the three-dimensional structures of proteins and protein complexes. However, crystals of large macromolecular complexes often diffract only weakly (yielding a resolution worse than 4 Å), so new methods that work at such low resolution are needed. Here a new method is described by which to obtain higher-quality electron density maps and more accurate molecular models of weakly diffracting crystals.

    • Gunnar F. Schröder
    • , Michael Levitt
    •  & Axel T. Brunger
  • Letter |

    Ultracold polar molecules offer the possibility of exploring quantum gases with interparticle interactions that are strong, long-range and spatially anisotropic. Here, dipolar collisions in an ultracold gas of fermionic potassium–rubidium molecules have been experimentally observed. The results show how the long-range dipolar interaction can be used for electric-field control of chemical reaction rates in an ultracold gas of polar molecules.

    • K.-K. Ni
    • , S. Ospelkaus
    •  & D. S. Jin
  • Article |

    A phase transition occurs when a physical system suddenly changes state, for instance when it melts or freezes. The Dicke model describes a collective matter–light interaction and has been predicted to show a quantum phase transition. Here, this quantum phase transition has been realized in an open system formed by a Bose–Einstein condensate coupled to an optical cavity. Surprisingly, the atoms are observed to self-organize into a supersolid phase.

    • Kristian Baumann
    • , Christine Guerlin
    •  & Tilman Esslinger
  • Letter |

    The precision of interferometers — used in metrology and in the state-of-the-art time standard — is generally limited by classical statistics. Here it is shown that the classical precision limit can be beaten by using nonlinear atom interferometry with Bose–Einstein condensates.

    • C. Gross
    • , T. Zibold
    •  & M. K. Oberthaler
  • Letter |

    Atom chips provide a versatile quantum laboratory for experiments with ultracold atomic gases, but techniques to control atomic interactions and to generate entanglement have been unavailable so far. Here, the experimental generation of multi-particle entanglement on an atom chip is described. The technique is used to produce spin-squeezed states of a two-component Bose–Einstein condensate, which should be useful for quantum metrology.

    • Max F. Riedel
    • , Pascal Böhi
    •  & Philipp Treutlein
  • Letter |

    A two-dimensional gas of electrons is a powerful test-bed for the fundamental physics of interacting particles, and has been much studied in the context of integer and fractional quantum Hall effects. The latest observations of this system reveal prominent structure in the high energy single particle spectrum that cannot be readily explained with existing models of this system.

    • O. E. Dial
    • , R. C. Ashoori
    •  & K. W. West
  • Letter |

    Until now, quantum atomic gases and single trapped ions have been treated separately in experiments. Now a hybrid system has been investigated, involving the immersion of a single trapped ion into a Bose–Einstein condensate of neutral atoms. The two systems could be controlled independently and the fundamental interaction processes were studied. Sympathetic cooling of the single ion by the condensate was observed, hinting at the possibility of using these condensates as refrigerators for ion-trap quantum computers.

    • Christoph Zipkes
    • , Stefan Palzer
    •  & Michael Köhl
  • Article |

    Quantum mechanics provides an accurate description of a wide variety of physical systems but it is very challenging to prove that it also applies to macroscopic (classical) mechanical systems. This is because it has been impossible to cool a mechanical mode to its quantum ground state, in which all classical noise is eliminated. Recently, various mechanical devices have been cooled to a near-ground state, but this paper demonstrates the milestone result of a piezoelectric resonator with a mechanical mode cooled to its quantum ground state.

    • A. D. O’Connell
    • , M. Hofheinz
    •  & A. N. Cleland
  • Letter |

    An insulator does not conduct electricity, and so cannot in general be used to transmit an electrical signal. But an insulator's electrons possess spin in addition to charge, and so can transmit a signal in the form of a spin wave. Here a hybrid metal–insulator–metal structure is reported, in which an electrical signal in one metal layer is directly converted to a spin wave in the insulating layer; this wave is then transmitted to the second metal layer, where the signal can be directly recovered as an electrical voltage.

    • Y. Kajiwara
    • , K. Harii
    •  & E. Saitoh
  • Review Article |

    • T. D. Ladd
    • , F. Jelezko
    •  & J. L. O’Brien
  • Letter |

    The phenomenon of superconductivity continues to intrigue, and several new superconducting materials have been discovered in recent years — but in the case of organic superconductors, no new material system with a high superconducting transition temperature has been identified in the past decade. Now it has been shown that the introduction of potassium into crystals of organic molecule picene can yield superconductivity at temperatures as high as 18 K.

    • Ryoji Mitsuhashi
    • , Yuta Suzuki
    •  & Yoshihiro Kubozono
  • Letter |

    In principle, it is possible to simulate some astrophysical phenomena inside the highly controlled environment of an atomic physics laboratory: previous work on the thermodynamics of a two-component Fermi gas (a system suited for such studies) led to thermodynamic quantities averaged over the trap. Now a general experimental method is reported that yields the equation of state of a uniform gas, providing new physical insights and enabling a detailed comparison with existing theories.

    • S. Nascimbène
    • , N. Navon
    •  & C. Salomon
  • Letter |

    One of the central predictions of general relativity is that a clock in a gravitational potential well runs more slowly than a similar clock outside the well. This effect, known as gravitational redshift, has been measured using clocks on a tower, an aircraft and a rocket, but here, laboratory experiments based on quantum interference of atoms are shown to produce a much more precise measurement.

    • Holger Müller
    • , Achim Peters
    •  & Steven Chu
  • Letter |

    The difference between the mass of an atom and the sum of its building blocks (the binding energy) is a manifestation of Einstein's famous relation E = mc2. Superheavy elements have been observed, but our present knowledge of the binding energy of these nuclides is based only on the detection of their decay products, although they represent the gateway to the predicted 'island of stability'. Here, direct mass measurements of trans-uranium nuclides are reported, providing reliable anchor points en route to the island of stability.

    • M. Block
    • , D. Ackermann
    •  & C. Weber
  • Letter |

    In the study of high-transition-temperature (high-Tc) copper oxide superconductors, a fundamental question is what symmetries are broken when the pseudogap phase sets in below a temperature T*. A large in-plane anisotropy of the Nernst effect is now observed in a high-Tc copper oxide superconductor that sets in precisely at T* throughout the doping phase diagram. It is concluded that the pseudogap phase is an electronic state that strongly breaks four-fold rotational symmetry.

    • R. Daou
    • , J. Chang
    •  & Louis Taillefer
  • Letter |

    The close binary Algol system contains a radio-bright KIV sub-giant star in a very close and rapid orbit with a main sequence B8 star. Evidence points to the existence of an extended, complex coronal magnetosphere originating at the cooler K subgiant, but the detailed morphology of the subgiant's corona and its possible interaction with its companion are unknown. Multi-epoch radio imaging of the Algol system now reveals a large coronal loop suggestive of a persistent asymmetric magnetic field structure aligned between the two stars.

    • W. M. Peterson
    • , R. L. Mutel
    •  & W. M. Goss
  • Letter |

    The Dirac equation successfully merges quantum mechanics with special relativity. It predicts some peculiar effects such as 'Zitterbewegung', an unexpected quivering motion of a free relativistic quantum particle. This and other predicted phenomena are key fundamental examples for understanding relativistic quantum effects, but are difficult to observe in real particles. Here, using a single trapped ion set to behave as a free relativistic quantum particle, a quantum simulation of the one-dimensional Dirac equation is demonstrated.

    • R. Gerritsma
    • , G. Kirchmair
    •  & C. F. Roos
  • Letter |

    Existing models of type Ia supernovae generally explain their observed properties, with the exception of the sub-luminous 1991bg-like supernovae. It has long been suspected that the merger of two white dwarfs could give rise to a type Ia event, but simulations so far have failed to produce an explosion. Here, a simulation of the merger of two equal-mass white dwarfs is presented that leads to a sub-luminous explosion; it requires a single common-envelope phase and component masses of about 0.9 solar masses.

    • Rüdiger Pakmor
    • , Markus Kromer
    •  & Wolfgang Hillebrandt
  • Letter |

    The amplitude of the magnetic field near the Galactic Centre has been uncertain by two orders of magnitude for several decades. A compilation of previous data now reveals a downward break in the region's non-thermal radio spectrum; this requires that the Galactic Centre field be at least 50 microgauss on 400 parsec scales, with evidence supporting a field of 100 microgauss. This would imply that over 10% of the Galaxy's magnetic energy is contained in only around 0.05% (or less) of its volume.

    • Roland M. Crocker
    • , David I. Jones
    •  & Raymond J. Protheroe
  • Letter |

    From earthquakes to hard drives, frictional motion and its strength are involved in a wide range of phenomena. The strength of an interface that divides two sliding bodies is determined by both the real contact area and the contacts' shear strength. By continuous measurements of the concurrent local evolution of the real contact area and the corresponding interface motion from the first microseconds when contact detachment occurs, frictional strength is now characterized from short to long timescales.

    • Oded Ben-David
    • , Shmuel M. Rubinstein
    •  & Jay Fineberg
  • Letter |

    The Southern Ocean is potentially a substantial sink of anthropogenic carbon dioxide; however, the regulation of this carbon sink by the wind-driven Ekman flow, mesoscale eddies and their interaction is under debate. Here, a high-resolution ocean circulation and carbon cycle model is used to study intra-annual variability in anthropogenic carbon dioxide over a two-year time period; the Ekman flow is found to be the primary mechanism of anthropogenic carbon dioxide transport across the Antarctic polar front.

    • T. Ito
    • , M. Woloszyn
    •  & M. Mazloff