Verifying the integrity of a tamper-indicating seal is crucial in surveillance and containment technologies, as an intruder may try to hide a breach. Seals based on the no-cloning principle of quantum mechanics offer an unprecedented level of security. By monitoring the entanglement of transmitted photon pairs, the authors detect intrusion attempts with 99.99% probability, and just a 10${}^{-9}$ chance for a false alarm. In contrast, any conventional optical system would fail this test completely.

City planners know how to stretch real estate: build upward. The same idea may be used to densify memory or other components on a chip. The authors demonstrate layer-selective microwave-assisted switching in a magnetic nanodot, exploiting the different ferromagnetic resonance frequencies of its two layers. This method presents a writing process for next-generation magnetic recording in three-dimensional media.

Measuring ultrasmooth layers of the important photovoltaic absorber CH${}_3$NH${}_3$PbI${}_3$, the authors find that earlier studies have seriously overestimated its absorption coefficients. Their calculations show that free-carrier generation occurs via nonexcitonic, semiconductor-type interband transitions within the PbI${}_3$ subunit. Using their revised optical constants, the quantum efficiency spectrum of a standard hybrid perovskite solar cell is reproduced very realistically. The wealth of information from this study enables depth-resolved optical simulations for the design of tomorrow’s CH${}_3$NH${}_3$PbI${}_3$ solar cells.

A promising approach for constructing networks of solid-state qubits for quantum information processing is the circuit QED architecture. In such a setup, the speed at which a qubit measurement can be turned on and off is limited by the time constant of a readout resonator. The authors demonstrate a method for populating and depopulating this resonator quickly and precisely, without prior knowledge of the qubit’s state—an elegant and practical technique to help speed up a quantum computer.

Verifying the integrity of a tamper-indicating seal is crucial in surveillance and containment technologies, as an intruder may try to hide a breach. Seals based on the no-cloning principle of quantum mechanics offer an unprecedented level of security. By monitoring the entanglement of transmitted photon pairs, the authors detect intrusion attempts with 99.99% probability, and just a 10${}^{-9}$ chance for a false alarm. In contrast, any conventional optical system would fail this test completely.

Moore’s Law has led to device dimensions approaching 10 nm in electronics, as spin-, tunneling- and phase-change-based devices are being explored to continue progress. The authors show a feasible scaling path to lead spin-torque logic to tomorrow’s technology. These scaling-parameter relationships and quantitative targets for magnetic materials, spin channels, and interfaces enable spintronics for low-power, high-performance computing, particularly in mobile devices.

City planners know how to stretch real estate: build upward. The same idea may be used to densify memory or other components on a chip. The authors demonstrate layer-selective microwave-assisted switching in a magnetic nanodot, exploiting the different ferromagnetic resonance frequencies of its two layers. This method presents a writing process for next-generation magnetic recording in three-dimensional media.

In security applications, explosives must be detected—preferably without being accidentally detonated! Light at terahertz (THz) frequencies offers a chemically specific and safe means to this end. The authors present a simulation method for rapidly identifying THz fingerprints of a large family of structurally anisotropic energetic materials, enabling accurate stand-off detection e.g. at airports or docks.

An optical resonator, as used in photonics, quantum information processing, and optical imaging, requires dynamical tweaking of its cavity length. The authors employ advanced control techniques to develop an approach for autonomously locking the frequency of an optical cavity, starting from any operating point, without failing in the nonlinear regime. Beyond technological improvements, this approach will be valuable for gravitational-wave interferometry, which could answer our questions about black holes, supernovae, and the Big Bang.

FePt is among the most widely used materials for data-storage technology, and recent experiments surprisingly suggest the possibility of all-optical control of its magnetization–without any external magnetic field. Sorting out the electronic temperature in the presence of heating from a laser burst, and any helicity dependence of the switching, is essential. Using a high-temperature micromagnetic model, the authors study ultrafast magnetization reversal in thin films of FePt exposed to laser pulses with linear and circular polarizations, to begin to clarify the critical details.

From computers to medicine, miniaturization approaches the atomic scale, where device operation can be dominated by quantum effects that are strongly coupled to the local environment. These influences may be seen not as a nuisance, but rather a nearly untapped source of information about physical or biochemical processes playing out nearby. How can one extract maximum information from such fluctuations with an atomic probe, under typical experimental constraints? The authors use quantum estimation theory to outline a general strategy for dynamical measurement of a broad class of environmental processes.

Hydrogen embrittlement of metallic alloys is critical to the aging and failure of components in power plants and infrastructure. Embrittlement begins with hydrogen penetrating the protective oxide film that naturally grows on a surface in air. The authors apply concepts from semiconductor defect physics and catalysis to develop materials engineering strategies for thwarting hydrogen uptake. For ZrO${}_2$ film on a Zr alloy, a model system that is important for materials in nuclear reactors, they demonstrate that one can use doping to tune the chemical potential of electrons in ZrO${}_2$ either to minimize the solubility of hydrogen, or to facilitate its evolution as H${}_2$ gas from the surface.

As electronics continue to shrink, heat management at the nanoscale has become increasingly important. The authors show that the thermal conductance at a metal-dielectric interface can be improved by half an order of magnitude by inserting just 1 nm of another metal. Multifunctional interfaces, as in plasmonic applications for heat-assisted magnetic recording, could exploit this thermal benefit with little impact on other properties.

Thin films are central to modern technologies ranging from semiconductors to metamaterials. The authors observe that by placing a subwavelength thin film at the node of an electromagnetic standing wave, it is possible to separate electric from magnetic dipole terms, or dipole from quadrupole terms, in the absorption spectrum. The technique is twice as sensitive as conventional measurements, functions at very low laser power, and reveals resonances that are invisible to existing spectroscopies. This approach could see application in analytical chemistry, condensed matter physics, nanotechnology, and forensic science.

High-temperature superconducting wires are promising for high-magnetic-field applications, such as compact, lightweight, powerful motors and generators. High current capacity is achieved by introducing controlled amounts of defects to pin dissipative magnetic vortices in the superconductor, but a systematic understanding of the optimal defect nanostructure remains elusive. The authors conduct realistic three-dimensional simulations of vortex dynamics in a real pinning landscape, reconstructed from STEM tomography of a cuprate sample. Impressive agreement with experiments indicates a promising pathway for future wire design.

Measuring ultrasmooth layers of the important photovoltaic absorber CH${}_3$NH${}_3$PbI${}_3$, the authors find that earlier studies have seriously overestimated its absorption coefficients. Their calculations show that free-carrier generation occurs via nonexcitonic, semiconductor-type interband transitions within the PbI${}_3$ subunit. Using their revised optical constants, the quantum efficiency spectrum of a standard hybrid perovskite solar cell is reproduced very realistically. The wealth of information from this study enables depth-resolved optical simulations for the design of tomorrow’s CH${}_3$NH${}_3$PbI${}_3$ solar cells.

An elastic sheet can be made to bend, twist, buckle, or wrinkle into a preprogrammed shape by employing a judicious distribution of differential strains. The authors review the mechanics behind such self-assembly, examples from nature, and state-of-the-art fabrication techniques. Engineering based on these phenomena has great potential across applications ranging from stretchable electronics and microactuators to drug delivery and self-assembled biological implants.