2020 Top 50 Physics Articles

Microcombs provide many opportunities for integration in optical communications systems. Here, the authors implement a soliton crystal microcomb as a tool to demonstrate more than 44 Tb/s communications with high spectral efficiency.

Semiconductor spin-qubits with CMOS compatible architectures could benefit from the industrial capacity of the semiconductor industry. Here, the authors make the first steps in demonstrating this by showing single electron operations within a two-dimensional array of foundry-fabricated quantum dots.

Open standard microscopy is urgently needed to give low-cost solutions to researchers and to overcome the reproducibility crisis in science. Here the authors present a 3D-printed, open-source modular microscopy toolbox UC2 (You. See. Too.) for a few hundred Euros.

The usual definition of external time is unlikely to survive if we want to unite quantum mechanics and relativity. Here the authors consider two quantum clocks moving in curved spacetime and formulate the probability distribution that relates their proper times, allowing them to explore quantum time dilation.

Establishing diagnostics for terrestrial exoplanets are crucial for their characterization. Here, the authors show brightness modulations of Venus are caused by planetary-scale waves superimposed on the super-rotating winds can be used to detect existence of an atmosphere if detected at an exoplanet.

It is hard to design quantum neural networks able to work with quantum data. Here, the authors propose a noise-robust architecture for a feedforward quantum neural network, with qudits as neurons and arbitrary unitary operations as perceptrons, whose training procedure is efficient in the number of layers.

Truly arbitrary spatiotemporal wavefront shaping has many potential applications in optics. Here the authors develop a system capable of arbitrary waveshaping to the extent of full time reversal of spatiotemporal optical beams.

Here, the authors show that Brown-Zak fermions in graphene-on-boron-nitride superlattices exhibit mobilities above 10⁶ cm²/V s and micrometer scale ballistic transport.

The origin of the covalent H–H bond is understood to be driven by kinetic energy lowering. Here the authors show this is not the case for bonds between heavier elements likely due to the presence of core electrons, and that constructive quantum interference instead drives bond formation.

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.

The tunability of disordered systems with a broadband response has not been explored. Here, the authors achieve the controlled manipulation of disordered plasmonic systems, realising a transition from broadband absorption to tunable reflection through control of the coupling to an external cavity.

Ultrafast imaging has been limited by the speed of electronic sensors. Here, the authors demonstrate single-shot compressed ultrafast spectral photography, which combines spectral encoding, pulse splitting, temporal shearing, and compressed sensing in order to achieve real-time imaging at 70 trillion frames per second.

Despite recent demonstrations of coherent spin-state transfer in arrays of spin qubits via exchange interaction, all-matter spin-state teleportation is still out of reach. Here the authors provide evidence for conditional teleportation of quantum-dot spin states, entanglement swapping, and gate teleportation.

Lithium niobate (LN) devices are promising for future photonic integrated circuits. Here, the authors demonstrate an electro-optic LN modulator with a very small modal volume based on photonic crystal resonator architecture.

The lack of scalable, high-quality insulators is a major problem hindering the progress on electronic devices built from 2D materials. Here, the authors review the current state-of-the-art and the future prospects of suitable insulators for 2D technologies.

Forecasting the state of health and remaining useful life of batteries is a challenge that limits technologies such as electric vehicles. Here, the authors build an accurate battery performance forecasting system using machine learning.

It’s still unclear whether entanglement can be generated, survive, and be observed in hot environments dominated by random collisions. Here, the authors use quantum non-demolition measurement on a hot alkali vapor to put more than ten trillion atoms in a long-lived and spatially extended entangled state.

Satellites with amateur radio communication capabilities have not been operated in lunar orbit before. Here, the authors present the design and performance of a VHF/UHF software-defined radio developed for and tested on lunar microsatellites.

Photoabsorption is a fundamental process that leads to changes in the electron density in matter. Here, the authors show a direct measurement of the distribution of electron density when a cyclohexadine molecule is excited by pulsed UV radiation and probed by a time delayed X-ray pulse generated at LCLS.

Optical elements play a crucial role in many modern systems, from cellphones to missiles. The miniaturization trend poses a challenge to optics, since classical lenses and mirrors tend to be bulky. One way of dealing with this challenge is using flat optics. For many years flat optics has been implemented using diffractive optics technology, but in the last two decades a new technology called metasurfaces has emerged. This technology does not replace diffractive optics, but rather expands on it, leveraging the new ability to manufacture subwavelength features on optical substrates. For imaging and focusing applications, diffractive lenses and metalenses are used, as a subset of diffractive optics and metasurfaces, respectively. Recently there has been debate over whether metalenses offer any real advantages over diffractive lenses. In this commentary we will try to gain some insight into this debate and present our opinion on the subject.

Conventional bioluminescence imaging usually operates in the visible region and its performance is limited by strong tissue absorption and scattering. Here, the authors present bioluminescence probes (BPs) with emission in the second near infrared (NIR-II) region, and show the NIR-II-BPs could sensitively recognize tumor metastasis with a high tumor-to-normal tissue ratio.

Analysing the space-time metric of quantum phenomena is complicated by the absence of a consistent theory of quantum gravity. Here, the authors show how to describe the space-time metric for multiple observers who are keeping time with quantum clocks, which interact gravitationally with each other.

Blue light-emitting diodes (LEDs) are critical for displays. Employing a large organic cation into a quasi-two dimensional perovskite with green emission, Chu et al. achieve LEDs exhibiting a high external quantum efficiency of 12.1% and stable spectra in the sky-blue region.

In quantum metrology (as well as computing) it is not easy to pinpoint the specific source of quantum advantage. Here, the authors reveal a link between postselection and the unusually high rates of information per final measurement in general quantum parameter-estimation scenarios.

Single atom catalysts (SACs) are promising in electrocatalysis but challenging to characterize. Here, the authors apply a recently developed quantum mechanical grand canonical potential kinetics method to predict reaction mechanisms and rates for CO₂ reduction at different sites of graphene-supported Ni-SACs.

Suitability for large-scale quantum computation imposes severe requirements on single-photon sources in terms of purity, indistinguishability and heralding efficiency. Here, the authors boost all these figures of merit through a dual-mode pump-delayed four-wave mixing scheme in low-loss silicon waveguides.

The experimental realization of lattice-born flat bands with nontrivial topology has been elusive. Here, the authors observe topological flat bands near the Fermi level in a kagome metal CoSn, with flat bands as well as Dirac bands originating from 3d orbitals in a frustrated kagome geometry.

Metal halide perovskites have been studied as promising materials for blue light-emitting diodes (LEDs) but the stability is still a bottleneck. Here Wang et al. develop a chelating additive strategy to increase efficiency, operational stability and color stability of blue perovskite LEDs.

Optical bioimaging in the second near-infrared (NIR-II, 1000–1700 nm) window exhibits abundant advantages. Here the authors report an organic NIR-II molecule with long blood circulation half-life time for continuous real-time monitoring of dynamic vascular processes.

Live cell imaging of mitochondrial cristae is challenged by the unsuitability of current fluorescent probes and high phototoxicity. Here the authors develop a squarine variant probe (MitoESq-635) that is capable of longitudinal imaging of cristae with STED with minimal phototoxicity.

Though wireless near-field communication (NFC) technologies that connect wearable sensors for health monitoring have been reported, the short range of NFC readers limits sensor functionality. Here, the authors report a wireless and battery-free body sensor network with near-field-enabled clothing.

The authors investigate the optical properties of a heterostructure formed by a metallic substrate and a nanostructured transition metal dichalcogenide multilayer by measuring the reflectance spectrum at different multilayer thicknesses, filling factors and grating periods. The spectra show strong dispersion and avoided crossing of excitons, plasmons and cavity photons along with excitonic mode suppression at the anti-crossing point.

Synthetic hair-like structures (cilia) controlled by an external field have been developed, especially for microfluidic applications. Here, Gu et al. make soft artificial cilia carpets with programmable magnetization patterns and utilize them to achieve pumping and locomotion in a soft robotic model.

Computer simulations of large-scale changes in membrane shape are challenging since they occur across a wide range of spatiotemporal scales. Here, authors present a multiscale algorithm that backmaps a continuum membrane model represented as a dynamically triangulated surface to its corresponding molecular model based on the coarse-grained Martini force field.

Scientific complementary metal-oxide semiconductor (sCMOS) cameras have advanced the imaging field, but they often suffer from additional noise compared to CCD sensors. Here the authors present a content-adaptive algorithm for the automatic correction of sCMOS-related noise for fluorescence microscopy.

The authors demonstrate wafer-scale, graphene-based ion sensitive field effect transistors arrays for simultaneous concentration measurement of K⁺, Na⁺, NH₄⁺, NO₃⁻, SO₄²⁻, HPO₄²⁻ and Cl⁻, and use their technology for real-time ion concentration measurements in an aquarium with lemnoideae lemna over a period of three weeks.

Real-time monitoring human motions normally demands connecting a large number of sensors in a complicated network. To make it simpler, Kim et al. decode the motion of fingers using a flexible sensor attached on wrist that measures skin deformation with the help of a deep-learning architecture.

While efficiency of nanocrystal-based devices has improved, charge transport within semiconductors assembled from nanocrystal quantum dots has remained unclear. Here, the authors use ab initio calculations to develop a predictive model for charge transport that also explains the origin of deep electronic traps and validate it experimentally.

Powerful terahertz pulses are generated during the nonlinear propagation of ultrashort laser pulses in gases. Here, the authors demonstrate efficient sub-cycle THz pulse generation by using two-color midinfrared femtosecond laser filaments in ambient air.

Terahertz imaging is promising in many applications, but still relies on complex equipment. Here, the authors develop a simplified solution that enables terahertz real-time imaging using a single-pixel detector and rapid reconstruction methods.

The combination of X-ray and neutron CT enables 4D studies, i.e. to explore the evolution of 3D structures with time. Here the authors apply this approach to a Li-ion primary cell, revealing elsewhere unseen trends in the spatial distribution of performance aided by a new ‘unrolling’ methodology.

Nanoantennas have been developed to direct light, but most still rely on laboratory scale light sources. Here, the authors demonstrate electrically-driven directional emission in the optical frequency range using a nanogap in conjunction with a Yagi-Uda antenna nanostructure.

Different methods are demonstrated in recent years to produce attosecond pulses. Here, the authors discuss recent development and future prospects of the generation of such pulses from gases and solids and their potential applications in spectroscopy and ultrafast dynamics in atoms, molecules and other complex systems.

The genome is folded in 3-dimensions, though the lack of robust ultra-resolution imaging makes this difficult to visualise. Here, the authors present 3D-EMISH that combines serial block-face scanning electron microscopy with in situ hybridization.

Conventional qubit readout methods in silicon spin qubits destroy the quantum state, precluding any further computations based on the outcome. Here, the authors demonstrate quantum non-demolition readout using a second qubit of the same kind, making for a scalable approach.

Perovskite light-emitting diodes have shown unexpected high external quantum efficiency of 20%, breaking the ray-optics limit. Here Cho et al. reveal that photon recycling is responsible for the enhancement and propose photonic structures to further improve the device efficiency.

Interaction between Cooper pairs and other collective excitations may reveal important information about the pairing mechanism. Here, the authors observe a universal jump in the phase of the driven Higgs oscillations in cuprate thin films, indicating the presence of a coupled collective mode, as well as a nonvanishing Higgs-like response at high temperatures, suggesting a potential nonzero pairing amplitude above Tc.

Lead halide perovskite quantum dots (PQDs) promise applications in optoelectronics but are limited by sensitivity to wet environments. Here the authors develop a Pb-S bonding approach to synthesize PQDs@silica nanodots that are capable of emitting and lasing in aqueous environments for long periods.

Two-dimensional hybrid perovskites are promising excitonic materials; however, there currently lacks understanding on exciton diffusion and annihilation. Here Deng et al. employ transient absorption microscopy to disentangle quantum-well-thickness-dependent exciton transport and annihilation in these materials.

Imagers capable of reconstructing three-dimensional scenes in the presence of strong background noise are desirable for many remote sensing and imaging applications. Here, the authors report an imager operating in photon-starved and noise-polluted environments through quantum parametric mode sorting.

Unique electronmagnetic response of Weyl semimetals have only been reported in static field regime. Here, the authors report evidence of a dynamical chiral anomaly response realized by internal collective lattice deformation with an external static magnetic field in a Weyl semimetal NbAs.