Volume 16 Issue 12, December 2020

An exactly solvable model for superconductivity includes two crucial features of the cuprates and sheds light on unexplained experiments.

The discussion of the quantum mechanical Wigner’s friend thought experiment has regained intensity. Recent theoretical results and experimental tests restrict the possibility of maintaining an observer-independent notion of measurement outcomes.

The Mott insulator ground state is a crucial feature of high-temperature superconductors such as the cuprates. Here, the authors find an exactly solvable model that contains both superconductivity and Mottness.

When a quantum system couples with its surroundings, macroscopic irreversibility emerges even though the microscopic Hamiltonian is itself time-reversal symmetric, causing the phenomena associated with certain symmetry-protected topological phases to be unstable.

A protocol for the reliable, efficient and precise characterization of quantum noise is reported and implemented in an architecture consisting of 14 superconducting qubits. Correlated noise within arbitrary sets of qubits can be easily detected.

Using doped BaFe₂As₂, the authors test whether nematicity is linked to superconductivity in the iron pnictides by applying the conjugate field to nematicity—a specific form of strain—and observe that the critical temperature decreases.

Transport and optical conductivity measurements reveal the non-Fermi liquid behaviour in correlated semimetal Nd₂Ir₂O₇. The result implies the emergent collective charge transport in this compound, not reconcilable with conventional band theory.

For a scenario of two separated but entangled observers, inequalities are derived from three fundamental assumptions. An experiment shows that these inequalities can be violated if quantum evolution is controllable on the scale of an observer.

A weak-to-strong quantum measurement transition has been observed in a single-trapped-ion system, where the ion’s internal electronic state and its vibrational motion play the roles of the measured system and the measuring pointer.

A time–information uncertainty relation in thermodynamics has been derived, analogous to the time–energy uncertainty relation in quantum mechanics, imposing limits on the speed of energy and entropy exchange between a system and external reservoirs.

Ultracold alkaline-earth fermionic atoms with large number of nuclear spin states possess SU(N) symmetry. That deeply affects their interaction properties, and allows a Fermi gas of these atoms to be cooled quickly to the quantum degenerate regime.

Scanning tunnelling microscopy is enhanced by microwave radiation that allows photon-assisted tunnelling processes. This technique is demonstrated on impurity states in a superconductor.

A magnetic impurity is placed on the tip of a scanning tunnelling microscope, allowing direct tunnelling between two Yu–Shiba–Rusinov bound states. This technique can probe and enhance the impurity state lifetime.

The authors investigate the relationship between the volume of malignant tumours and their metabolic processes using a large dataset of patients with cancer. They find that cancers follow a superlinear metabolic scaling law, which implies that the proliferation of cancer cells accelerates with increasing volume.

Within the Hartree atomic unit systems, the Schrödinger equation becomes parameter free. But there’s more to it than making a student’s life easier, as Gordon Drake and Eite Tiesinga recount.