Quantum physics articles within Nature Communications

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  • Article |

    Topological phases are unusual states of matter whose properties are robust against small perturbations. Using a photonic quantum walk system, Kitagawaet al. simulate one-dimensional topological phases and reveal novel topological phenomena far from the static or adiabatic regimes.

    • Takuya Kitagawa
    • , Matthew A. Broome
    •  & Andrew G. White

  • Article |

    Geometrically frustrated spin systems are a class of statistical mechanical models that have received widespread attention, especially in condensed matter physics. This study experimentally demonstrates a quantum information processor that can simulate the behaviour of such frustrated spin system.

    • Jingfu Zhang
    • , Man-Hong Yung
    •  & Jonathan Baugh

  • Article |

    The electromotive force is a well established phenomenon that is induced by a varying magnetic field. Here, Tanabeet al. report a compelling experimental confirmation of its spin-induced analogue, the spinmotive force.

    • K. Tanabe
    • , D. Chiba
    •  & T. Ono

  • Article |

    Nitrogen-vacancy colour centres in diamond are promising examples for solid-state multi-spin-qubit systems. Here, the spin environment of nitrogen vacancy centres is studied spectroscopically, uncovering a mechanism for spin-flip suppression that opens the way for quantum information applications.

    • N. Bar-Gill
    • , L.M. Pham
    •  & R. Walsworth

  • Review Article |

    Quantum-mechanical tunnelling currents across nanometre-scale gaps between electrodes are sensitive to the medium in the gap. Albrecht reviews progress towards using tunnelling currents to probe single-molecule processes, and in biosensor and sequencing applications.

    • T. Albrecht

  • Article
    | Open Access

    As lengthscales in plasmonic structures enter the sub-nanometre regime, quantum effects become increasingly important. Here, a quantum-corrected model is presented that addresses quantum effects in realistic-sized plasmonic structures, a situation not feasible for full-quantum-mechanical simulations.

    • Ruben Esteban
    • , Andrei G. Borisov
    •  & Javier Aizpurua

  • Article |

    Quantum phase transitions are generally associated with many-body quantum systems undergoing changes between different phases. This study examines the connection between such phase transitions and quantum information processing, and finds that different quantum phases can have different computational power.

    • Jian Cui
    • , Mile Gu
    •  & Vlatko Vedral

  • Article |

    Electron spins at nitrogen-vacancy centres in diamond are thought to be the most promising building blocks for practical realizations of quantum computers. Yaoet al. present a scalable architecture for a quantum information processor based on such vacancy centres that operates at room temperature.

    • N.Y. Yao
    • , L. Jiang
    •  & M.D. Lukin

  • Article |

    Percolation transitions indicate the threshold above which a network can operate. This work examines a general class of models known as hierarchical networks, and shows they can be made to percolate explosively, if they share features of so-called 'small-world' networks.

    • Stefan Boettcher
    • , Vijay Singh
    •  & Robert M. Ziff

  • Article |

    Stochastic processes play an important role in a broad range of scientific problems. This study demonstrates that a large class of such processes are most efficiently simulated by quantum mechanical models, thus reducing the complexity required to simulate them using classical models.

    • Mile Gu
    • , Karoline Wiesner
    •  & Vlatko Vedral

  • Article
    | Open Access

    Point defects in diamond in the form of nitrogen vacancy centres are believed to be promising candidates for qubits in quantum computers. Grotzet al. present a method for manipulating the charge state of nitrogen vacancies using an electrolytic gate electrode.

    • Bernhard Grotz
    • , Moritz V. Hauf
    •  & Jose A. Garrido

  • Article |

    The spin–orbit interaction affects the electronic structure of many solids to give rise to a host of unusual phenomena. Bahramyet al.theoretically examine its role in the non-centrosymmetric compound BiTeI, and find that under the application of pressure, it leads to topologically insulating behaviour.

    • M.S. Bahramy
    • , B.-J. Yang
    •  & N. Nagaosa

  • Article |

    The dynamics of isolated quantum systems can either be strongly correlated with their initial state, or chaotic, as they relax into thermal equilibrium. Olshaniiet al. present a simple, exactly solvable model that captures the transition between these two limiting cases, and suggests it may have some universal features.

    • Maxim Olshanii
    • , Kurt Jacobs
    •  & Vladimir A. Yurovsky

  • Article
    | Open Access

    Although they offer significant promise, practical implementations of quantum key distribution are often not as rigorous as theory predicts. This study demonstrates how two instances of such discrepancies can be resolved by taking advantage of an enotropic formulation of the uncertainty principle.

    • Marco Tomamichel
    • , Charles Ci Wen Lim
    •  & Renato Renner

  • Article
    | Open Access

    Quantum mechanics predicts that objects can simultaneously exist in a superposition of two states. Kneeet al.propose and demonstrate experimentally a protocol which fully confirms this prediction, by testing the so-called Leggett–Garg inequality in a non-invasive manner.

    • George C. Knee
    • , Stephanie Simmons
    •  & Simon C. Benjamin

  • Article
    | Open Access

    When two spatially separated parties flip a coin, it is impossible to choose between two alternatives in an unbiased manner. This study presents a quantum coin-flipping protocol that overcomes this problem and ensures a dishonest party cannot bias the outcome completely.

    • Guido Berlín
    • , Gilles Brassard
    •  & Wolfgang Tittel

  • Article |

    Generation of multipartite entanglement between quantum states is crucial for developing quantum computation systems, although it has proven harder to achieve for photons than ions. Here, an eight-photon entangled state based on four independent photon pairs is observed, beating the previous record of six.

    • Yun-Feng Huang
    • , Bi-Heng Liu
    •  & Guang-Can Guo

  • Article
    | Open Access

    Most quantum communication experiments are performed at visible wavelengths, yet practical, long-range schemes need photons in the telecommunications range. Here, down-conversion of a visible photon to the near-infrared is demonstrated, while retaining its entanglement to another visible photon.

    • Rikizo Ikuta
    • , Yoshiaki Kusaka
    •  & Nobuyuki Imoto

  • Article
    | Open Access

    In the theory of general relativity time flows at different rates depending on the space–time geometry. Here, a drop in the visibility of a quantum 'clock' interference in a gravitational potential is predicted, which cannot be explained without the general relativistic notion of time.

    • Magdalena Zych
    • , Fabio Costa
    •  & Časlav Brukner

  • Article
    | Open Access

    Quantum-mechanical predictions are generally probabilistic. Here, assuming freely chosen measurements, it is shown that enhanced predictions are not possible and, thus, randomness is inherent in quantum theory: a result that has applications in fields such as quantum cryptography.

    • Roger Colbeck
    •  & Renato Renner

  • Article
    | Open Access

    Quantum computing has advantages over conventional computing, but the complexity of quantum algorithms creates technological challenges. Here, an architecture-independent technique, that simplifies adding control qubits to arbitrary quantum operations, is developed and demonstrated.

    • Xiao-Qi Zhou
    • , Timothy C. Ralph
    •  & Jeremy L. O'Brien

  • Article |

    Pagerank is widely used to rank web content; however, it is unknown how network topology affects its performance. The authors demonstrate that, in random networks, pagerank is sensitive to perturbations in topology, whereas scale-free networks contain a few super-stable nodes whose ranking is exceptionally stable.

    • Gourab Ghoshal
    •  & Albert-László Barabási

  • Article
    | Open Access

    In some iron-based materials, unconventional superconductivity can emerge near a quantum phase transition where long-range magnetic order vanishes. Giovannettiet al.show that the magnetic quantum phase transition in an iron pnictide superconductor is very close to the quantum tricritical point.

    • Gianluca Giovannetti
    • , Carmine Ortix
    •  & José Lorenzana

  • Article
    | Open Access

    The fractional quantum Hall effect occurs when electrons move in Landau levels. In this study, using a theoretical flat-band lattice model, the fractional quantum Hall effect is observed in the presence of repulsive interactions when the band is one third full and in the absence of Landau levels.

    • D.N. Sheng
    • , Zheng-Cheng Gu
    •  & L. Sheng

  • Article |

    A quantum simulator can follow the evolution of a prescribed model, whose behaviour may be difficult to determine. Here, the emergence of magnetism is simulated by implementing a quantum Ising model, providing a benchmark for simulations in larger systems.

    • R. Islam
    • , E.E. Edwards
    •  & C. Monroe

  • Article
    | Open Access

    Two-qubit operation is an essential part of quantum computation, but implementation has been difficult. Gotoet al.introduce optically controllable internuclear coupling in semiconductors providing a simple way of switching inter-qubit couplings in semiconductor-based quantum computers.

    • Atsushi Goto
    • , Shinobu Ohki
    •  & Tadashi Shimizu

  • Article |

    Anyons are particles with fractional statistics that interpolate between bosons and fermions, and are thought to exist in low-dimensional systems. Keilmannet al. propose an experimental system to create anyons in one-dimensional optical lattices using assisted Raman tunnelling.

    • Tassilo Keilmann
    • , Simon Lanzmich
    •  & Marco Roncaglia

  • Article |

    A quantum key distribution system allows two remote parties to communicate in secret by a shared key code. This work demonstrates a complete and undetected eavesdropping attack on a quantum key distribution connection, highlighting the need for further security updates on secure communication systems.

    • Ilja Gerhardt
    • , Qin Liu
    •  & Vadim Makarov

  • Article
    | Open Access

    Observing superposition states of mesoscopic quantum systems is an ongoing challenge. Gerlichet al. report quantum interference of large tailor-made organic compounds, demonstrating delocalization and the quantum wave nature of entire molecules composed of up to 430 atoms.

    • Stefan Gerlich
    • , Sandra Eibenberger
    •  & Markus Arndt

  • Article |

    Graphene and InAs nanowires are both promising materials for coherent spin manipulation, but coupling between a quantum system and its environment leads to decoherence. Here, the contribution of electron–phonon coupling to decoherence in graphene and InAs nanowire is studied.

    • P. Roulleau
    • , S. Baer
    •  & T. Ihn

  • Article
    | Open Access

    Multimode interference devices could allow the implementation of multiport circuits for quantum technologies. Here, quantum interference is demonstrated in 2×2 and 4×4 multimode interference devices, and a technique is reported to characterize such devices.

    • Alberto Peruzzo
    • , Anthony Laing
    •  & Jeremy L. O'Brien

  • Article |

    Quantum-enhanced measurements use quantum mechanical effects to enhance measurement sensitivity of classical quantities; but the required quantum states are generally highly entangled and difficult to produce. In this study, the use of entangled states is avoided allowing Heisenberg-limited measurements.

    • Daniel Braun
    •  & John Martin

  • Article |

    The nonlocality of a quantum state is often difficult to predict. Here, Cavalcanti and colleagues devise a method based on networks that makes this characterization much easier, revealing that the nonlocality of a quantum state depends on the context of the measurement.

    • Daniel Cavalcanti
    • , Mafalda L. Almeida
    •  & Antonio Acín

  • Article |

    Error correction in quantum computing can be implemented using transversal gates, which in turn rely on the availability of so-called magic states. The authors experimentally show that it is possible to improve the fidelity of these states by distilling five of them into one.

    • Alexandre M. Souza
    • , Jingfu Zhang
    •  & Raymond Laflamme

  • Article |

    Direct quantum state tomography—deducing the state of a system from measurements—is mostly unfeasible due to the exponential scaling of measurement number with system size. The authors present two new schemes, which scale linearly in this respect, and can be applied to a wide range of quantum states.

    • Marcus Cramer
    • , Martin B. Plenio
    •  & Yi-Kai Liu

  • Article |

    Two principles have recently been proposed as attempts to provide physical axioms for quantum mechanics: causality and macroscopic locality. Cavalcanti and colleagues show here that the two are not equivalent, giving confidence in information causality as a constraint for correlations obtained in experiments.

    • Daniel Cavalcanti
    • , Alejo Salles
    •  & Valerio Scarani

  • Article
    | Open Access

    Molecular fluctuations are a source of noise that can impede single-molecule identification. Here, quantum-fluctuation-induced inelastic noise is observed as current fluctuations in individual molecules, suggesting that inelastic noise could be used as a molecular signature.

    • Makusu Tsutsui
    • , Masateru Taniguchi
    •  & Tomoji Kawai

  • Article
    | Open Access

    Signal processing by time reversal has thus far only been realized through nonlinear mechanisms. The authors describe an all-linear, and thus low-power, time-reversal process based on frequency inversion in a dynamically controlled artificial periodic structure, a dynamic magnonic crystal.

    • Andrii V. Chumak
    • , Vasil S. Tiberkevich
    •  & Burkard Hillebrands

  • Review Article |

    Gravitational waves are predicted by general relativity, but their direct observation from astronomical sources hinges on large improvements in detection sensitivity. The authors review how squeezed light and other quantum optical concepts are being applied in the development of next generation interferometric detectors.

    • Roman Schnabel
    • , Nergis Mavalvala
    •  & Ping K. Lam

  • Article |

    In low-temperature one-dimensional metals, electrons condense into collective charge-density wave states. Zybtsevet al. observe conductivity jumps with temperature in a metal bar, as only specific wavelengths are permitted in the bar for the charge-density wave modes.

    • S.G. Zybtsev
    • , V.Ya. Pokrovskii
    •  & S.V. Zaitsev-Zotov

  • Article |

    Routing packets on the growing and changing underlying structure of the Internet is challenging and currently based only on local connectivity. Here, a global Internet map is devised: with a greedy forwarding algorithm, it is robust with respect to network growth, and allows speeds close to the theoretical best.

    • Marián Boguñá
    • , Fragkiskos Papadopoulos
    •  & Dmitri Krioukov

  • Article |

    Electrons in metals at extremely high magnetic fields show interesting quantum structures. The authors measure the angle-dependent Nernst effect with high precision and show that, for bismuth, Coulomb interactions between the electrons become important in this ultraquantum regime.

    • Huan Yang
    • , Benoît Fauqué
    •  & Kamran Behnia

  • Article |

    The magnetic flux lines in a superconductor present intricate patterns, whose origins are seldom understood. Here the authors link them to geometrical effects by means of the 'hairy ball' theorem, which states that for a vector field on a sphere there will always be at least one singularity.

    • Mark Laver
    •  & Edward. M. Forgan

  • Article |

    Quantum communication applications require memories capable of storing multiple qubits. To implement scalable architectures for this purpose, Usmani and coworkers turn to a rare-earth doped silicate, in which they demonstrate coherent and reversible mapping of 64 optical modes at the single photon level.

    • Imam Usmani
    • , Mikael Afzelius
    •  & Nicolas Gisin

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