Quantum physics articles within Nature Physics

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  • Article |

    Fast particles propagating through a classical medium give rise to shock waves. Calculations now uncover the surprising behaviour of particles in one-dimensional quantum fluids: a fast particle will never come to a full stop, and a supersonic particle will propagate through the medium undergoing long-lived oscillations.

    • Charles J. M. Mathy
    • , Mikhail B. Zvonarev
    •  & Eugene Demler

  • Letter |

    Entanglement is an important resource in quantum-enhanced technologies, but it is difficult to generate, especially in solid-state systems. An experiment now demonstrates the entanglement of two nuclear spins via a parity measurement of the electron spin in a nitrogen-vacancy centre in diamond.

    • Wolfgang Pfaff
    • , Tim H. Taminiau
    •  & Ronald Hanson

  • Research Highlights |

    The 2012 Nobel Prize in Physics has been awarded to Serge Haroche and David J. Wineland "for ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems".

    • Iulia Georgescu

  • Letter |

    A two-level quantum system driven by an electromagnetic field can oscillate between its two states. The effects of these so-called Rabi oscillations are usually obscured in many-body systems by the variation in properties of the particles involved. Now, however, coherent many-body Rabi oscillations are observed in a vapour made up of several hundred cold rubidium atoms.

    • Y. O. Dudin
    • , L. Li
    •  & A. Kuzmich

  • Letter |

    Shor’s quantum algorithm factorizes integers, and implementing this is a benchmark test in the early development of quantum processors. Researchers now demonstrate this important test in a solid-state system: a circuit made up of four superconducting qubits factorizes the number 15.

    • Erik Lucero
    • , R. Barends
    •  & John M. Martinis

  • 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
    •  & 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
    •  & Ping Koy Lam

  • Letter |

    Nuclear spin is seen as a robust qubit. Electrons can be used to ‘read’ to the nuclear state, but their presence causes decoherence. Researchers now show that this problem can be circumvented using a temporary spin state, thus enabling entanglement of the nuclear state at unprecedented speeds.

    • Vasileia Filidou
    • , Stephanie Simmons
    •  & John J. L. Morton

  • News & Views |

    Single electrons in quantum dots can be disturbed by the apparatus used to measure them. The disturbance can be mediated by incoherent phonons — literally, noise. Engineering acoustic interference could negate these deleterious effects and bring quantum dots closer to becoming a robust quantum technology.

    • Thaddeus D. Ladd

  • Letter |

    Density functional theory provides a powerful framework for probing electronic structure in many-body systems. A new functional for particles interacting via short-range potentials extends its applicability to ultracold atoms in optical lattices.

    • Ping Nang Ma
    • , Sebastiano Pilati
    •  & Xi Dai

  • Letter |

    Hilbert space is made up of a potentially infinite number of dimensions that correspond to all the parameters needed to fully define a system. The idea is seen as an important resource for quantum information processing. A technique for estimating the number of dimensions in an unknown system based on the results of measurements performed on it—a so-called dimension witness—is now experimentally demonstrated.

    • Johan Ahrens
    • , Piotr Badzia̧g
    •  & Mohamed Bourennane

  • Letter |

    Is it possible to deduce the number of dimensions of a completely unknown system only from the results of measurements performed on it? So-called dimension witnesses allow such an estimation, and are now experimentally demonstrated using pairs of entangled photons.

    • Martin Hendrych
    • , Rodrigo Gallego
    •  & Juan P. Torres

  • Letter |

    You influence a system by measuring it. This back-action is an important consideration when studying tiny structures in which quantum effects play a crucial role. Researchers now show that quantum interference could provide a way to negate back-action in quantum-dot-qubit circuits.

    • G. Granger
    • , D. Taubert
    •  & A. S. Sachrajda

  • Letter |

    A quantum memory that combines high-efficiency and long lifetime is now demonstrated. Employing a collective excitation, or spin wave, in an ensemble of atoms in a trap improves memory lifetime, while incorporating the trap into an optical ring cavity simultaneously aids higher retrieval efficiency.

    • Xiao-Hui Bao
    • , Andreas Reingruber
    •  & Jian-Wei Pan

  • News & Views |

    Do quantum states offer a faithful representation of reality or merely encode the partial knowledge of the experimenter? A new theorem illustrates how the latter can lead to a contradiction with quantum mechanics.

    • Scott Aaronson

  • News & Views |

    Quantum non-locality can improve the quality of sources of randomness.

    • Serge Massar

  • Article |

    A no-go theorem on the reality of the quantum state is demonstrated. If the quantum state merely represents information about the physical state of a system, then predictions that contradict those of quantum theory are obtained.

    • Matthew F. Pusey
    • , Jonathan Barrett
    •  & Terry Rudolph

  • Letter |

    Bell’s equations enable scientists to test the fundamental implications of quantum physics. A central tenet of this idea is that the choice of measurement is truly random. Researchers now show that some Bell experiments can even increase randomness in cases where choice is not entirely free. The concept could increase the usefulness of weakly random sources for more thorough tests of quantum mechanics.

    • Roger Colbeck
    •  & Renato Renner

  • Research Highlights |

    • Iulia Georgescu

  • Article |

    In 2000, Asher Peres put forward the paradoxical idea that entanglement could be produced after the entangled particles have been measured, even if they no longer exist. Researchers now experimentally demonstrate this idea using four photons.

    • Xiao-song Ma
    • , Stefan Zotter
    •  & Anton Zeilinger

  • Commentary |

    The long-term promises of quantum simulators are far-reaching. The field, however, also needs clearly defined short-term goals.

    • J. Ignacio Cirac
    •  & Peter Zoller

  • Review Article |

    Experimental progress in controlling and manipulating trapped atomic ions has opened the door for a series of proof-of-principle quantum simulations. This article reviews these experiments, together with the methods and tools that have enabled them, and provides an outlook on future directions in the field.

    • R. Blatt
    •  & C. F. Roos

  • Progress Article |

    Lithographically fabricated micrometre-scale superconducting circuits exhibit behaviour analogues to natural quantum entities, such as atom, ions and photons. Large-scale arrays of such circuits hold the promise of providing a unique route to quantum simulation. Recent progress in technology and methodology are reviewed here, and prospects and challenges discussed.

    • Andrew A. Houck
    • , Hakan E. Türeci
    •  & Jens Koch

  • Review Article |

    Quantum optics has played an important role in the exploration of foundational issues in quantum mechanics, and in using quantum effects for information processing and communications purposes. Photonic quantum systems now also provide a valuable test bed for quantum simulations. This article surveys the first generation of such experiments, and discusses the prospects for tackling outstanding problems in physics, chemistry and biology.

    • Alán Aspuru-Guzik
    •  & Philip Walther

  • Review Article |

    Experiments with ultracold quantum gases provide a platform for creating many-body systems that can be well controlled and whose parameters can be tuned over a wide range. These properties put these systems in an ideal position for simulating problems that are out of reach for classical computers. This review surveys key advances in this field and discusses the possibilities offered by this approach to quantum simulation.

    • Immanuel Bloch
    • , Jean Dalibard
    •  & Sylvain Nascimbène

  • Article |

    Commutation relations define the limit to which two complementary properties can be simultaneously known—Heisenberg’s uncertainty principle. Yet it is thought that these canonical relations might be different in the quantum gravity regime. Researchers now show how quantum-optics experiments might provide a direct route for studying these effects.

    • Igor Pikovski
    • , Michael R. Vanner
    •  & Časlav Brukner

  • Letter |

    A cross-validation study comparing experimental findings obtained with a system of ultracold fermions with the results of a method based on computing contributions from millions of Feynman diagrams underlines the potential of the so-called bold diagrammatic Monte Carlo technique for solving problems in the area of strongly correlated quantum matter.

    • K. Van Houcke
    • , F. Werner
    •  & M. W. Zwierlein

  • News & Views |

    Squeezed states push the limits of quantum measurement precision, but observing them is never straightforward. In spin-1 Bose–Einstein condensates, an elegant algebra reveals squeezed states that would otherwise go unnoticed.

    • Austen Lamacraft

  • Letter |

    Squeezed states—which permit precision beyond the scope of Heisenberg’s uncertainty relation—are well established for spin-1/2 particles. Now an elegant demonstration of squeezing in spin-1 condensates generalizes the criteria for squeezed states to higher spin dimensions.

    • C. D. Hamley
    • , C. S. Gerving
    •  & M. S. Chapman

  • News & Views |

    A single photon can alter the shape of a molecule. It is now shown that quantum effects can play an important role in this change leading to conformation relaxation rates hundreds of times faster than previously expected.

    • Shaul Mukamel

  • Article |

    A molecule can alter shape as it absorbs a photon. It is now shown that quantum effects can play an important role in this change leading to conformation rates hundreds of times faster than previously expected.

    • J. Clark
    • , T. Nelson
    •  & G. Lanzani

  • News & Views |

    Two-qubit entanglement can be preserved by partially measuring the qubits to leave them in a 'lethargic' state. The original state is restored using quantum measurement reversal after the qubits have travelled through a decoherence channel.

    • Alexander N. Korotkov

  • Letter |

    According to Heisenberg, the more precisely, say, the position of a particle is measured, the less precisely we can determine its momentum. The uncertainty principle in its original form ignores, however, the unavoidable effect of recoil in the measuring device. An experimental test now validates an alternative relation, and the uncertainty principle in its original formulation is broken.

    • Jacqueline Erhart
    • , Stephan Sponar
    •  & Yuji Hasegawa

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