Volume 16 Issue 2, 2 February 2020

Physics is formulated in terms of timeless, axiomatic mathematics. A formulation on the basis of intuitionist mathematics, built on time-evolving processes, would offer a perspective that is closer to our experience of physical reality.

Lack of reproducibility is not necessarily bad news; it may herald new discoveries and signal scientific progress.

Planets are assembled from the ground up, beginning with millimetre-sized interstellar dust grains. Microgravity experiments suggest that centimetre-sized dust aggregates form from these smaller grains via collisional charging.

An electoral model predicts that polarized and alienated voters lead to unstable elections, like phase transitions in an Ising model. Such physics-inspired models may help political scientists devise electoral reforms to quench instability.

Qubits cannot exist without nonlinearity, but nonlinear elements in superconducting circuits lead to losses. A superconducting qubit has now been realized by nonlinearly coupling two microwave resonators, offering the promise of long coherence times.

A layer-by-layer study of TaSe₂ shows how this material becomes increasingly insulating as it thins to a monolayer. Scanning tunnelling microscopy reveals the electronic correlations underlying this insulator with atomic resolution.

Finding ground states of given Hamiltonians is crucial for quantum simulation — a promising application of quantum computers. An algorithm now finds these states using minimal resources, making it implementable in near-term noisy devices.

This Review Article outlines the techniques necessary for the manipulation of neutral atoms and making use of their interactions, when excited to Rydberg states, to achieve the goal of quantum simulation of many-body physics.

Continuous-variables quantum information processing requires non-Gaussian states and operations. The generation of non-Gaussian quantum states of a multimode field is now reported through a mode-selective photon-subtraction scheme

Four single-photon states are generated and entangled on a single micrometre-scale silicon chip, and provide the basis for the demonstration of chip-to-chip quantum teleportation.

The authors use spin waves to demonstrate that charged quantum Hall skyrmions exist away from integer filling. They also see evidence of several fractional skyrmion states.

Short pulses of light shift the balance between two competing charge density wave phases, allowing the weaker one to manifest transiently while suppressing the stronger one. This shows that competing phases can be tuned in a non-equilibrium setting.

The microscopic quantum Hall edge currents and the equilibrium currents that generate the mirror magnetic monopoles in time-reversal-symmetry-broken topological matter are directly imaged in the quantum Hall state in graphene by using a SQUID-on-tip.

Charge-carrier dynamics are fundamental to the operation and performance of semiconductor devices. In methylammonium lead iodide perovskites, carriers in the non-equilibrium regime after excitation propagate ballistically over 150 nm within 20 fs.

The measurement of the dielectric constant combined with ab initio calculations of the polarizability and the virial coefficient of helium provides a new primary pressure standard, which is complementary to the mechanical standard.

In inertial confinement fusion experiments, the effect of the overlapping laser beams on the plasma is predicted to lead to a distortion of the electron distribution function, which has now been observed in experiments.

In a mathematical model of democratic elections, electoral instability is shown to be linked to negative representation, which occurs when a shift in electoral opinions pushes the election outcome in the opposite direction.

The internal structure of the neutron has now been probed by highly energetic photons scattering off it. Combined with previous results for protons, these measurements reveal the contributions of quark flavours to the nucleon structure.

A general method is proposed to calculate the out-of-time-ordered correlators (OTOCs) in one-dimensional systems. Motivated by the results obtained from its application to various systems, a universal form for the dynamics of OTOCs is conjectured.

The quantum imaginary time evolution and Lanczos algorithms offer a resource-efficient way to compute ground or excited states of target Hamiltonians on quantum computers. This offers promise for quantum simulation on near-term noisy devices.

A flux-tunable inductive coupling between two microwave superconducting resonators allows the operation of one of them as a two-level system. The lifetime is limited by the oscillator’s quality factor, offering potential for highly coherent qubits.

The electrons that contribute to the Mott insulator state in single-layer 1T-TaSe2 are shown to also have a rich variation in their orbital occupation. As more layers are added, both the insulating state and orbital texture weaken.

In our understanding of planetary formation, it is still unclear how millimetre-sized dust grains grow into centimetre-sized aggregates. Microgravity experiments now show that electrical charging of the grains leads to the formation of larger clumps.

The note A tuned to 440 Hz only became the norm for musical performance in 1939 after decades of international and interdisciplinary disputes. Fanny Gribenski retraces this rocky path.