Sensing at the limit

The authors introduce the concept of electromagnetic canyons and non-resonance amplification for optical detection of nanoscale objects. They demonstrate that a pair of nanowire sensors enable detection of 25-nm radii objects with a standard widefield microscope.

Tautomerization, the interconversion between two constitutional isomers of a molecule, plays a major role in chemistry. The combination of hyper-resolved fluorescence microscopy with time-correlated measurements and spectral selection enables the identification and in-depth characterization of a tautomerization reaction within a single molecular switch.

The authors demonstrate that individual atoms on a surface can be detected and distinguished from each other with subångström resolution using the electron spin resonance.

Driving single-electron tunnelling in synchronization with the oscillations of the conductive tip of an atomic force microscope allows mapping of the electronic structure of individual molecules in different charge states.

THz dual comb spectroscopy may be performed using down-converted or quantum cascade laser systems, forcing a choice between absolute frequency referencing and high sensitivity. Here, these strengths are combined in a hybrid, dual frequency comb spectrometer, capable of high-accuracy measurements on molecular transitions.

Operating a laser gyroscope near an exceptional point has been shown to enhance its responsivity. However, here the authors demonstrate in theory and experiment that the enhanced responsivity is exactly compensated by increased noise that is inherent to this system near the exceptional point.

A wavelength-scanned LiDAR offers high spatial resolution and can dynamically adapt to fast moving scenes.

A massively parallel coherent light detection and ranging (lidar) scheme using a soliton microcomb—a light source that emits a wide spectrum of sharp lines with equally spaced frequencies—is described.

The internal electron dynamics of submicrometre devices are hard to resolve because of bandwidth limitations of current measurement techniques. Here, the authors sample the 250 GHz coherent oscillation of a single-electron wave packet inside a quantum dot at 4.2 K employing a resonant level.

Using a femtosecond mode-locked laser and a frequency-locked electric signal, a displacement measurement method that offers a >MHz measurement speed, sub-nanometre precision and a measurement range of more than several millimetres is achieved, facilitating the study of broadband, transient and nonlinear mechanical dynamics in real time.

A pair of transportable optical lattice clocks with 10⁻¹⁸ uncertainty is developed. The relativistic redshift predicted by the theory of general relativity has been tested at the 10^–5 level by the two optical clocks with a height difference of 450 m on the ground.

External stimuli can induce significant changes in the magnetisation of a material; however, these changes can occur very rapidly, making measurements difficult. Herein the authors demonstrate a method of ultrafast magnetometry, enabling the detection of the rapid magnetization changes.

Techniques for imaging through scattering media are generally invasive, operate at microscopic scales or require a priori information. Here, the authors overcome these limitations by introducing confocal diffuse tomography, which captures the 3D shape of objects hidden behind scattering media.

Optical microscopy is limited to shallow in vivo imaging depths owing to the exponential extinction of single-scattered waves by multiple light scattering. In this Review, we survey methodologies for deep optical imaging that maintain microscopic resolution by making deterministic use of multiple-scattered waves.

Imaging methods in microscopy seek to simultaneously optimize spatial resolution, contrast and imaging speed even in large specimen. Here, a combination of holographic phase shaping, fluorophores-switching, and dynamic blocking of fluorescence is used to improve resolution, sectioning and imaging depth in light-sheet microscopy.

A DNA-based voltmeter non-invasively measures the membrane potential of organelles.