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Volume 17 Issue 10, October 2021

Volume 17 Issue 10

Topological frequency combs

Optical frequency combs are a key technology in communications, sensing and metrology. A theoretical proposal shows that introducing topological principles into their design makes on-chip combs more efficient and robust against fabrication defects.

See Mittal et al. and Peano

Image: David Lam. Cover Design:Allen Beattie


  • Editorial |

    Publicly funded nuclear fusion laboratories are experiencing competition from the private sector, giving new energy to the field.


Books & Arts

Research Highlights

News & Views

  • News & Views |

    Some material defects have quantum degrees of freedom that are measurably disturbed by environmental changes, making them excellent sensors. A two-dimensional material with such defects could improve the versatility of quantum-sensing technologies.

    • J.-P. Tetienne
  • News & Views |

    In a study on high-harmonic generation from a dense atomic xenon gas, the strong-field light–matter interaction is shown to leave a quantum mechanical imprint on the incident light that escapes the semiclassical picture of strong-field physics.

    • Thomas Fennel
  • News & Views |

    A microscopy technique allows the identification of parameters in a paradigmatic model of condensed-matter physics.

    • Isabel Guillamón
  • News & Views |

    Light propagating in the topological edge channel of an array of ring resonators is predicted to generate nested frequency combs: like a Matryoshka doll containing a set of smaller dolls, each ‘tooth’ of the comb comprises another frequency comb.

    • Vittorio Peano
  • News & Views |

    The tin isotope 100Sn is key to understanding nuclear stability, but little is known about its properties. Precision measurements of closely related indium isotopes have now pinned down its mass.

    • Nunzio Itaco
  • News & Views |

    The state that forms at low temperatures in a quantum antiferromagnet on a kagome lattice has been debated for decades. Nuclear magnetic resonance has now shown the gradual emergence of entangled spin singlets in a disordered kagome antiferromagnet.

    • Martin Klanjšek
  • News & Views |

    Scanning tunnelling microscopy reveals an unexpected periodicity in the local density of states of a transition metal dichalcogenide — with a puzzling wavelength that casts the material as a quantum spin liquid.

    • Carmen Rubio-Verdú
    • Abhay N. Pasupathy
  • News & Views |

    Polaritons are hybrid states of light and matter that occur in a wide range of physical platforms. When a nanosphere is levitated inside an optical cavity, light can hybridize with the motion on a plane rather than along an axis, resulting in ‘vectorial’ polaritons.

    • Tania S. Monteiro


  • Perspective |

    The interaction between light and the crystal lattice of a quantum material can modify its properties. Utilizing nonlinear interactions allows this to be done in a controlled way to design specific non-equilibrium functionalities.

    • Ankit S. Disa
    • Tobia F. Nova
    • Andrea Cavalleri
  • Perspective |

    Network representations of complex systems are limited to pairwise interactions, but real-world systems often involve higher-order interactions. This Perspective looks at the new physics emerging from attempts to characterize these interactions.

    • Federico Battiston
    • Enrico Amico
    • Giovanni Petri



  • Article |

    Entangled photon states can be used to make quantum information more robust. A photonic experimental implementation with eight qubits shows that error-protection schemes can increase the success rate of running a quantum algorithm.

    • Caterina Vigliar
    • Stefano Paesani
    • Anthony Laing
  • Article |

    The hyperfine states of ultracold polar molecules are a strong candidate for storing quantum information. Identifying and eliminating all detectable causes of decoherence has extended the qubit coherence time beyond 5.6 s in RbCs molecules.

    • Philip D. Gregory
    • Jacob A. Blackmore
    • Simon L. Cornish
  • Article |

    Moiré potentials substantially alter the electronic properties of twisted bilayer graphene at a magic twist angle. A propagating plasmon mode, which can be observed with optical nano-imaging, is associated with transitions between the moiré minibands.

    • Niels C. H. Hesp
    • Iacopo Torre
    • Frank H. L. Koppens
  • Article |

    Optical frequency combs are a key technology in precision time keeping, spectroscopy and metrology. A theoretical proposal shows that introducing topological principles into their design makes on-chip combs more efficient and robust against fabrication defects.

    • Sunil Mittal
    • Gregory Moille
    • Mohammad Hafezi

Amendments & Corrections

Measure for Measure

  • Measure for Measure |

    The measurement of pH is more complicated than it seems, recalls Andrea Taroni.

    • Andrea Taroni


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