Volume 20 Issue 7, July 2024

High harmonic generation has long been successfully described using the semi-classical three-step model. However, recent progress has introduced a quantum optical formulation, exposing the limitations of the semi-classical picture.

Questioning the validity of axioms can teach us about physics beyond the standard model. A recent search for the violation of charge conservation and the Pauli exclusion principle yields limits on these scenarios.

A superfluid is a macroscopic system with zero viscosity through which entropy is reversibly transported by waves. An unexpected transport phenomenon has now been observed between two superfluids, where irreversible entropy transport is enhanced by superfluidity.

In solids, the quantum metric captures the quantum coherence of the electron wavefunctions. Recent experiments demonstrate the detection and manipulation of the quantum metric in a noncollinear topological antiferromagnet at room temperature.

The determination of the order parameter symmetry is a critical issue in the study of unconventional superconductors. Ultrasound measurements on UTe₂, a candidate spin-triplet superconductor, now provide evidence for the single-component nature of its order parameter.

The rotation of holes jumping between quantum dots in silicon quantum computers creates additional complexity for two-qubit operations. Understanding the rules of this somersaulting movement is key to the progress of hole-based qubit technology.

Spatial heterogeneity in disease transmission rates and in mixing patterns between regions makes predicting epidemic trajectories hard. Quantifying the mixing rates within and between spatial regions can improve predictions.

Laser-driven acceleration is a promising path towards more compact machines. Now, proton beams with energies up to 150 MeV have been achieved with a repetitive petawatt laser.

A practical and hardware-efficient blueprint for fault-tolerant quantum computing has been developed, using quantum low-density-parity-check codes and reconfigurable neutral-atom arrays. The scheme requires ten times fewer qubits and paves the way towards large-scale quantum computing using existing experimental technologies.

As counterparts to optical frequency combs, magnonic frequency combs could have broad applications if their initiation thresholds were low and the ‘teeth’ of the comb plentiful. Progress has now been made through exploiting so-called exceptional points to enhance the nonlinear coupling between magnons and produce wider magnonic frequency combs.

The nuclear pore complex of eukaryotic cells senses the mechanical directionality of translocating proteins, favouring the passage of those that have a leading mechanically labile region. Adding an unstructured, mechanically weak peptide tag to a translocating protein increases its rate of nuclear import and accumulation, suggesting a biotechnological strategy to enhance the delivery of molecular cargos into the cell nucleus.

Plasmonic excitations can enhance the interaction between a metal and molecules adsorbed onto its surface. This Review summarizes the different effects involved in this process and places them into a framework based on electron scattering.

The Majorana Demonstrator experiment reports searches for the violation of the Pauli exclusion principle and of charge conservation. In the absence of a signal, exclusion limits for these processes are reported.

Quantum low-density parity-check codes are highly efficient in principle but challenging to implement in practice. This proposal shows that these codes could be implemented in the near term using recently demonstrated neutral-atom arrays.

Connecting two superfluid reservoirs leads to both particle and entropy flow between the systems. Now, a direct measurement of the entropy current and production in ultracold quantum gases reveals how superfluidity enhances entropy transport.

A Dirac quantum spin liquid phase is predicted to have a continuum of fractionalized spinon excitations with a Dirac cone dispersion. A spin continuum consistent with this picture has now been observed in neutron scattering measurements.

Controlling orbital magnetic moments for applications can be difficult. Now local probes of a kagome material, TbV₆Sn₆, demonstrate how the spin Berry curvature can produce a large orbital Zeeman effect that can be tuned with a magnetic field.

Manipulation of the quantum-metric structure to produce topological phenomena has rarely been studied. Now, flexible control of the quantum-metric structure is demonstrated in a topological chiral antiferromagnet at room temperature.

Leggett modes can occur when superconductivity arises in more than one band in a material and represent oscillation of the relative phases of the two superconducting condensates. Now, this mode is observed in Cd₃As₂, a Dirac semimetal.

The symmetry of the superconducting order parameter in UTe₂ is still debated. Now ultrasound experiments suggest that the order parameter can only have one component.

Some magnetic phase transitions can be understood as Bose–Einstein condensation of magnons. Close to a quantum critical point, YbCl₃ now provides a realization of a Bose–Einstein condensate that is dominated by two-dimensional physical behaviour.

Frequency combs, which are important for applications in precision spectroscopy, depend on material nonlinearities for their function, which can be hard to engineer. Now an approach combining magnons and exceptional points is shown to be effective.

The ferromagnet CrVI₆ serves as a material platform to demonstrate the topological Kerr effect in two-dimensional magnets. This can be used to identify skyrmions by magneto-optical means.

A successful silicon spin qubit design should be rapidly scalable by benefiting from industrial transistor technology. This investigation of exchange interactions between two FinFET qubits provides a guide to implementing two-qubit gates for hole spins.

The hybrid architecture of Andreev spin qubits made using semiconductor–superconductor nanowires means that supercurrents can be used to inductively couple qubits over long distances.

Linear topological systems can be characterized using invariants such as the Chern number. This concept can be extended to the nonlinear regime, giving rise to nonlinearity-induced topological phase transitions.

As amorphous solids, glasses and gels are similar, but the origins of their different elastic properties are unclear. Simulations now suggest differing free-energy-minimizing pathways: structural ordering for glasses and interface reduction for gels.

Protein transport across the nuclear membrane is regulated by the nuclear pore complex. Experiments now show that the rates of nuclear transport rely on the presence of locally mechanically soft regions of the transported proteins.

Cells can form a rotating doublet. This rotation is driven by the symmetry breaking of myosin polarization in the cortices of the two cells.

Spatial dynamics can obscure epidemic trends from surveillance data, biasing reproduction ratio estimates over long periods. A spectral correction reweights incidence data to remove this bias, thus improving monitoring to inform response strategies.

Laser-driven proton acceleration experiments achieve energies of up to 150 MeV with particle yields that are relevant for applications such as radiobiology.

It has many names and yet no name. The designation of the universal gas constant as R has remained a mystery, as Karen Mudryk recounts.