Volume 18 Issue 2, February 2022

As in-person conferences begin to make a return, we look forward to the opportunity to reconnect.

Entanglement can provide an extra boost in precision, but entangled states are hard to detect. A recent experiment solves this problem by letting the entangling dynamics come full circle — or not, depending on the subtle perturbation to be sensed.

Superconducting devices ubiquitously have an excess of broken Cooper pairs, which can hamper their performance. It is widely believed that external radiation is responsible but a study now suggests there must be an additional, unknown source.

Although the mass of the electron antineutrino is still eluding direct measurement, the KATRIN experiment with its huge spectrometer has pushed the sensitivity below a billionth of the proton mass.

Observations of an electronic state where rotational symmetry is broken show that this could be a generic feature of moiré materials.

The dynamics of quantum information and entanglement is closely linked to the physics of thermalization. A quantum simulator comprised of superconducting qubits has measured the spread of quantum information in a many-body system.

Acoustic waveguides have been used to implement the long-theorized phenomenon of non-Abelian braiding, in which abstract geometric constructions are used to generate transformations between different modes.

When crystal defects are present in an ensemble of spinning colloids that induce transverse forces on each other, the defects assemble into grain boundaries that can break the system apart into a set of crystal whorls.

Superconductivity and ordered states formed by interactions—both of which could be unconventional—have recently been observed in a family of kagome materials.

The performance of superconducting devices can be degraded by quasiparticle generation mechanisms that are difficult to identify and eliminate. Now, a small superconducting island can be kept quasiparticle free for seconds at a time.

A semiconductor platform for experimentally investigating the multiorbital Bose–Hubbard model with long-range interactions is demonstrated. The interactions between the excitons are strong enough to reach the Mott insulator regime.

Active matter exhibits a plethora of collective phenomena in both biological and artificial systems. In a model system of colloidal rollers, polar states in active liquids can be controlled.

In its second measurement campaign, the Karlsruhe Tritium Neutrino experiment achieved a sub-electronvolt sensitivity on the effective electron anti-neutrino mass.

Nonlinear interferometry based on time reversal enables entanglement-enhanced measurements without the need for low-noise detection. An alternative approach now exploits cyclic dynamics and shows performance beyond the standard quantum limit.

The complexity of many-body quantum states makes their evolution difficult to simulate with classical computers. Experiments on a 2D nine-qubit device demonstrate that the key properties of quantum lattices can be accessed by measuring out-of-time-ordered correlators.

Although it shows promise for applications, non-Abelian braiding is difficult to realize in electronic systems. Its demonstration using acoustic waveguides may provide a useful platform to study non-Abelian physics.

A general theoretical technique is introduced to identify materials that host flat bands. Applying topological quantum chemistry provides the generating bases for these flat bands in all space groups.

Cuprates exhibit exotic states because of the interplay between spin, charge and orbital degrees of freedom. Ab initio calculations now show that a mechanism called orbital expansion plays a key role in the magnetic properties of cuprates.

Observations of an electronic nematic phase in twisted double bilayer graphene expand the number of moiré materials where this interaction-driven state exists.

Comparing ways of arranging catalysts in living systems reveals that the reaction- and diffusion-limited regimes require different strategies. The formalism generalizes the Thomson problem of optimizing the configuration of electrons on a sphere.

The addition of transverse forces to an ensemble of colloidal spinners induces the appearance of odd elastic crystals, featuring self-propelled defects that organize the system into a ‘self-kneading’ crystal whorl state.

The establishment of a global metric system of units as agreed upon in the Metre Convention relies on international as well as national institutes and organizations, of which Stefanie Reichert gives an overview.