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Children can experience scientific concepts by using materials in their everyday world to perform safe and fun experiments.

The search for electron spin qubits A point defect in diamond known as the nitrogen-vacancy (N-V) centre has generated a great deal of interest because it has a highly localized electronic spin state with quantum properties that can be easily accessed at room temperature. The search is on for similar defects in other semiconductors that are easier to grow and process into devices than diamond, or that offer alternative functionalities. Here Koehl et al . describe a new range of defect spin states in silicon carbide that can be optically addressed in the telecommunications wavelength range and coherently controlled up to room temperature. Their spin coherence properties are comparable to those of the diamond N-V centre, and silicon carbide is a material for which extensive microfabrication processes already exist in the semiconductor industry. These materials are therefore promising candidates for photonic, spintronic and quantum information applications. Electronic spins in semiconductors have been used extensively to explore the limits of external control over quantum mechanical phenomena 1 . A long-standing goal of this research has been to identify or develop robust quantum systems that can be easily manipulated, for future use in advanced information and communication technologies 2 . Recently, a point defect in diamond known as the nitrogen–vacancy centre has attracted a great deal of interest because it possesses an atomic-scale electronic spin state that can be used as an individually addressable, solid-state quantum bit (qubit), even at room temperature 3 . These exceptional quantum properties have motivated efforts to identify similar defects in other semiconductors, as they may offer an expanded range of functionality not available to the diamond nitrogen–vacancy centre 4 . Notably, several defects in silicon carbide (SiC) have been suggested as good candidates for exploration, owing to a combination of computational predictions and magnetic resonance data 4 , 5 , 6 , 7 , 8 , 9 , 10 . Here we demonstrate that several defect spin states in the 4H polytype of SiC (4H-SiC) can be optically addressed and coherently controlled in the time domain at temperatures ranging from 20 to 300 kelvin. Using optical and microwave techniques similar to those used with diamond nitrogen–vacancy qubits, we study the spin-1 ground state of each of four inequivalent forms of the neutral carbon–silicon divacancy, as well as a pair of defect spin states of unidentified origin. These defects are optically active near telecommunication wavelengths 11 , and are found in a host material for which there already exist industrial-scale crystal growth 12 and advanced microfabrication techniques 13 . In addition, they possess desirable spin coherence properties that are comparable to those of the diamond nitrogen–vacancy centre. This makes them promising candidates for various photonic, spintronic and quantum information applications that merge quantum degrees of freedom with classical electronic and optical technologies 2 , 14 , 15 , 16 , 17 .

Weyl semimetals are predicted to exhibit a host of unusual transport properties. NbP, a system predicted to share characteristics of both normal and Weyl semimetals, is now shown to have a very large, non-saturating magnetoresistance. Recent experiments have revealed spectacular transport properties in semimetals, such as the large, non-saturating magnetoresistance exhibited by WTe 2 (ref.  1 ). Topological semimetals with massless relativistic electrons have also been predicted 2 as three-dimensional analogues of graphene 3 . These systems are known as Weyl semimetals, and are predicted to have a range of exotic transport properties and surface states 4 , 5 , 6 , 7 , distinct from those of topological insulators 8 , 9 . Here we examine the magneto-transport properties of NbP, a material the band structure of which has been predicted to combine the hallmarks of a Weyl semimetal 10 , 11 with those of a normal semimetal. We observe an extremely large magnetoresistance of 850,000% at 1.85 K (250% at room temperature) in a magnetic field of up to 9 T, without any signs of saturation, and an ultrahigh carrier mobility of 5 × 10 6 cm 2 V −1 s −1 that accompanied by strong Shubnikov–de Haas (SdH) oscillations. NbP therefore presents a unique example of a material combining topological and conventional electronic phases, with intriguing physical properties resulting from their interplay.

\"Explains how to use the scientific method to conduct several science experiments about the properties of matter. Includes ideas for science fair projects\"--Provided by publisher.

Plasmons are directly launched in graphene, and their key parameters — propagation and attenuation — are studied with near-field infrared nano-imaging. Voltage-controlled graphene plasmonics Plasmonic devices, which exploit surface plasmons (electromagnetic waves that propagate along the surface of metals) offer the possibility of controlling and guiding light at subwavelength scales. All eyes are on graphene — atom-thick layers of carbon — as a promising platform for plasmonic applications because it can strongly interact with light and host surface plasmons in the infrared range. Two independent groups reporting in this issue of Nature show that plasmons can be directly launched in graphene, and observed with near-field optical microscopy. Moreover, the wavelengths and amplitudes of the plasmons can be tuned by a gate voltage, a promising capability for the development of on-chip graphene photonics for use in applications including telecommunications and information processing. Surface plasmons are collective oscillations of electrons in metals or semiconductors that enable confinement and control of electromagnetic energy at subwavelength scales 1 , 2 , 3 , 4 , 5 . Rapid progress in plasmonics has largely relied on advances in device nano-fabrication 5 , 6 , 7 , whereas less attention has been paid to the tunable properties of plasmonic media. One such medium—graphene—is amenable to convenient tuning of its electronic and optical properties by varying the applied voltage 8 , 9 , 10 , 11 . Here, using infrared nano-imaging, we show that common graphene/SiO 2 /Si back-gated structures support propagating surface plasmons. The wavelength of graphene plasmons is of the order of 200 nanometres at technologically relevant infrared frequencies, and they can propagate several times this distance. We have succeeded in altering both the amplitude and the wavelength of these plasmons by varying the gate voltage. Using plasmon interferometry, we investigated losses in graphene by exploring real-space profiles of plasmon standing waves formed between the tip of our nano-probe and the edges of the samples. Plasmon dissipation quantified through this analysis is linked to the exotic electrodynamics of graphene 10 . Standard plasmonic figures of merit of our tunable graphene devices surpass those of common metal-based structures.

Learn what water is, how we use it, and why our world may be running dry.

Demonstration of an optomechanical system that works as a quantum interface between light and micro-mechanical motion. Nanomechanical oscillators coupled to optic cavities The possibility of controlling the quantum states of micro- and nanomechanical oscillators has been of great interest in recent years. Although various mechanical resonators have been cooled to their quantum ground state, there are few reports of experiments in which this quantum regime is further explored and used, for example, to exchange quantum information. Previously, quantum coupling between mechanical degrees of freedom and microwave radiation has been shown. Now, Verhagen et al . demonstrate an optomechanical system, cooled by radiation pressure, that works as a quantum interface between a mechanical oscillator and optical photons, offering the advantage that standard optical fibres can be used to extract the quantum information. Optical laser fields have been widely used to achieve quantum control over the motional and internal degrees of freedom of atoms and ions 1 , 2 , molecules and atomic gases. A route to controlling the quantum states of macroscopic mechanical oscillators in a similar fashion is to exploit the parametric coupling between optical and mechanical degrees of freedom through radiation pressure in suitably engineered optical cavities 3 , 4 , 5 , 6 . If the optomechanical coupling is ‘quantum coherent’—that is, if the coherent coupling rate exceeds both the optical and the mechanical decoherence rate—quantum states are transferred from the optical field to the mechanical oscillator and vice versa. This transfer allows control of the mechanical oscillator state using the wide range of available quantum optical techniques. So far, however, quantum-coherent coupling of micromechanical oscillators has only been achieved using microwave fields at millikelvin temperatures 7 , 8 . Optical experiments have not attained this regime owing to the large mechanical decoherence rates 9 and the difficulty of overcoming optical dissipation 10 . Here we achieve quantum-coherent coupling between optical photons and a micromechanical oscillator. Simultaneously, coupling to the cold photon bath cools the mechanical oscillator to an average occupancy of 1.7 ± 0.1 motional quanta. Excitation with weak classical light pulses reveals the exchange of energy between the optical light field and the micromechanical oscillator in the time domain at the level of less than one quantum on average. This optomechanical system establishes an efficient quantum interface between mechanical oscillators and optical photons, which can provide decoherence-free transport of quantum states through optical fibres. Our results offer a route towards the use of mechanical oscillators as quantum transducers or in microwave-to-optical quantum links 11 , 12 , 13 , 14 , 15 .

\"Make a simple refrigerator like pottery-maker Mohammed Bah Abba did that does not use electricity, or create little models of people out of ice like sculptor Nâele Azevedo. This title gives readers both an understanding of the different states of matter and the skills to investigate great discoveries and works. Exciting and easy-to-understand experiments encourage budding scientists, inventors, engineers, and artists to stand on the shoulders of the curious and creative people who came before them.\"-- Provided by publisher.

Aerotaxy, an aerosol-based growth method, is used to produce gallium arsenide nanowires with a growth rate of about 1 micrometre per second, which is 20 to 1,000 times higher than previously reported for traditional nanowires and allows sensitive and reproducible control of the nanowires’ optical and electronic properties. Tunable nanowires synthesized Nanowires hold promise for a variety of applications in electronics, energy and biomedical technologies. However, a major hurdle is the large-scale production of high-quality nanowires. In this paper, Lars Samuelson and colleagues develop a low-cost aerosol-based synthesis of gallium arsenide (GaAs) nanowires with throughput substantially better than achieved by conventional methods. The method produces high-quality nanowires with tunable dimensions, good optical properties and spectral uniformity. Semiconductor nanowires are key building blocks for the next generation of light-emitting diodes 1 , solar cells 2 and batteries 3 . To fabricate functional nanowire-based devices on an industrial scale requires an efficient methodology that enables the mass production of nanowires with perfect crystallinity, reproducible and controlled dimensions and material composition, and low cost. So far there have been no reports of reliable methods that can satisfy all of these requirements. Here we show how aerotaxy, an aerosol-based growth method 4 , can be used to grow nanowires continuously with controlled nanoscale dimensions, a high degree of crystallinity and at a remarkable growth rate. In our aerotaxy approach, catalytic size-selected Au aerosol particles induce nucleation and growth of GaAs nanowires with a growth rate of about 1 micrometre per second, which is 20 to 1,000 times higher than previously reported for traditional, substrate-based growth of nanowires made of group III–V materials 5 , 6 , 7 . We demonstrate that the method allows sensitive and reproducible control of the nanowire dimensions and shape—and, thus, controlled optical and electronic properties—through the variation of growth temperature, time and Au particle size. Photoluminescence measurements reveal that even as-grown nanowires have good optical properties and excellent spectral uniformity. Detailed transmission electron microscopy investigations show that our aerotaxy-grown nanowires form along one of the four equivalent 〈111〉B crystallographic directions in the zincblende unit cell, which is also the preferred growth direction for III–V nanowires seeded by Au particles on a single-crystal substrate. The reported continuous and potentially high-throughput method can be expected substantially to reduce the cost of producing high-quality nanowires and may enable the low-cost fabrication of nanowire-based devices on an industrial scale.