Some like it hot (but others do not): Photonic engineered textiles are of significant interest for personal thermal regulation, as they can keep a person comfortable over a large temperature range, and provide the potential for substantial energy savings. However, yarn- or fiber-based dual-mode designs that provide both cooling and heating functionalities have been absent. By staggering metallic and dielectric fibers within a yarn, the authors propose an effective double-sided textile to achieve a large emissivity contrast between the two surfaces of the fabric.

Integrated photon sources play a key role in quantum information science, but source nonuniformity prevents all circuit elements from being connected coherently. The authors address this longstanding challenge via birefringence engineering and nonlinear interaction locking in femtosecond-laser direct writing, to yield 128 uniform quantum sources integrated in a single chip. These sources are tunable via different pumping regimes, for applications at large scale and high dimension in both discrete- and continuous-variable approaches. This demonstrated scalability and uniformity of quantum sources will enable large-scale all-on-chip quantum processors for real-world applications.

Understanding spin-charge interconversion (SCI) in topological quantum materials, such as Dirac semimetals, is important for developing energy-efficient spintronic memory. This article reports room-temperature measurements of SCI at the interface between an archetypal Dirac semimetal (Cd${}_3$As${}_2$) and a metallic ferromagnet (Ni${}_{0.8}$Fe${}_{0.2}$). Analysis shows that a Dirac semimetal can have a SCI efficiency similar to that of heavy metals and topological insulators. Surprisingly, the highest efficiency is associated with extrinsic effects due to imperfect (oxidized) interfaces. These results suggest caution in attributing spin transport solely to the topological states of Cd${}_3$As${}_2$.

Quantum defects in diamond are a rapidly developing platform, with applications ranging from precision sensing to quantum information processing (QIP) to dark matter (DM) detection. Such defects are strongly affected by local strain, so advancing this platform requires tools to interrogate strain at the nanoscale. Using scanning x-ray diffraction microscopy, the authors demonstrate the measurement and three-dimensional mapping of strain features in quantum-defect-enhanced diamond with nanometer-scale spatial resolution. Beyond enabling a future diamond-based directional DM detector, this technique should advance the materials engineering of strained diamonds for QIP and sensing.

Alice lives on Venus, Bob lives on Mars… The biggest problem in their communication is to establish a common reference frame, so that they can use quantum cryptography for their secret letters. To help them, this study proposes a method for entanglement quantification that does $not$ rely on synchronized reference frames. Counterintuitively, measurements in random and unknown bases can be used to establish just how entangled a quantum state is. This strategy may prove useful in complex quantum communication networks, where establishing a common reference frame (measurement basis) is impractical or impossible.

Spin Hall nano-oscillators can generate radio-frequency output from direct-current input, and being planar structures with well defined geometry leaves them suitable for integration into microwave technologies. Control over output amplitude and frequency can be achieved by tuning magnetic field and direct current, but little is known about how these oscillators respond to input that changes rapidly, on the nanosecond time scale. This study shows that input current pulses just a few ns in duration are sufficient to generate rf output. Also, pulsing current and external rf inputs further improves the frequency and amplitude stability of the magnetization oscillations.

The authors address a critical roadblock in the development of topological qubits: charge impurities within semiconductor-superconductor hybrid structures. Majorana zero modes may occur in such nanowires and hold promise as the building blocks of topological quantum computers, but disorder in the system can destroy these modes. This work shows that charge impurities within the semiconductor lead to serious complications, with direct implications for the development of Majorana-based qubits. Upper limits are found for the level of charge-impurity density that still allows Majorana zero modes to emerge, providing clear direction for what needs to be done to achieve real-world progress.

Optical pump-probe setups are commonly used for excitation and investigation of the spin dynamics in various types of magnetic materials. Usually spatially homogeneous excitation is considered, but here the authors describe the optical excitation of the $nonuniform$ terahertz spin dynamics that are due to the intrinsic anisotropic properties of a weakly ferromagnetic material. They furthermore present an approach for probing and restoring the spatial distribution inside a magnetic crystal, which allows one to properly interpret the experimental results and obtain the complete picture of nonuniform terahertz spin dynamics.

The classical buckling problem, studied by Euler himself, is still important in many fields where macroscale or nanoscale structures may fail under compression. The impact of discrete or atomic structure on the critical buckling load is of paramount interest, yet the physics is still insufficiently understood. This study combines experiment and theory to solve that enigma: Phonon dispersion relations are at the heart of the physics of the buckling of both discrete and continuous structures. This insight will have an impact on engineering solutions, from nanostructures where molecular details prevail, to medical stents that naturally feature discretized polygonal symmetry.

To cool off, don’t turn on the fan; turn on the stereo! Acoustically enhanced heat transfer currently relies on traveling waves, but recent theoretical work suggest that stationary waves in such inhomogeneous media would generate more intense streaming flows. This experiment reports the additional heat flux achieved by forcing the first acoustic mode in a cavity filled with stably stratified air. Significant cooling is observed, especially as the top-to-bottom temperature difference is increased. This acoustic streaming effect could be used to cool remote locations with transducers that last a very long time.

Fast, ultrasensitive electrometers have been instrumental to the advancement of basic science. However, many applications (such as readout of quantum-dot-based qubits, and mediation of optomechanical interactions) could benefit from operating such charge sensors at low power. Here the authors demonstrate a charge sensitivity of 14 $\mu e/\sqrt{\mathrm{Hz}}$ with a cavity-embedded Cooper-pair transistor (CCPT) using 16 aW of power, which corresponds to the single-photon level of the cavity. These results support the feasibility of using a CCPT to mediate an optomechanical interaction that reaches the single-photon strong-coupling regime.

The 2- to 2.5-$\mu$m waveband enjoys reduced solar background and low propagation losses in the atmosphere and hollow-core optical fibers. However, harnessing these advantages for optical quantum communications has proved challenging due to a lack of suitable quantum light sources and detectors. The authors demonstrate in this waveband a source of entangled photons that is suitable for generating secure keys for quantum key distribution, and provide device-independent certification of the entanglement. These results are promising for the future implementation of device-independent secure optical quantum communications in daylight.

Some like it hot (but others do not): Photonic engineered textiles are of significant interest for personal thermal regulation, as they can keep a person comfortable over a large temperature range, and provide the potential for substantial energy savings. However, yarn- or fiber-based dual-mode designs that provide both cooling and heating functionalities have been absent. By staggering metallic and dielectric fibers within a yarn, the authors propose an effective double-sided textile to achieve a large emissivity contrast between the two surfaces of the fabric.

Integrated photon sources play a key role in quantum information science, but source nonuniformity prevents all circuit elements from being connected coherently. The authors address this longstanding challenge via birefringence engineering and nonlinear interaction locking in femtosecond-laser direct writing, to yield 128 uniform quantum sources integrated in a single chip. These sources are tunable via different pumping regimes, for applications at large scale and high dimension in both discrete- and continuous-variable approaches. This demonstrated scalability and uniformity of quantum sources will enable large-scale all-on-chip quantum processors for real-world applications.

Understanding spin-charge interconversion (SCI) in topological quantum materials, such as Dirac semimetals, is important for developing energy-efficient spintronic memory. This article reports room-temperature measurements of SCI at the interface between an archetypal Dirac semimetal (Cd${}_3$As${}_2$) and a metallic ferromagnet (Ni${}_{0.8}$Fe${}_{0.2}$). Analysis shows that a Dirac semimetal can have a SCI efficiency similar to that of heavy metals and topological insulators. Surprisingly, the highest efficiency is associated with extrinsic effects due to imperfect (oxidized) interfaces. These results suggest caution in attributing spin transport solely to the topological states of Cd${}_3$As${}_2$.

Quantum defects in diamond are a rapidly developing platform, with applications ranging from precision sensing to quantum information processing (QIP) to dark matter (DM) detection. Such defects are strongly affected by local strain, so advancing this platform requires tools to interrogate strain at the nanoscale. Using scanning x-ray diffraction microscopy, the authors demonstrate the measurement and three-dimensional mapping of strain features in quantum-defect-enhanced diamond with nanometer-scale spatial resolution. Beyond enabling a future diamond-based directional DM detector, this technique should advance the materials engineering of strained diamonds for QIP and sensing.

Alice lives on Venus, Bob lives on Mars… The biggest problem in their communication is to establish a common reference frame, so that they can use quantum cryptography for their secret letters. To help them, this study proposes a method for entanglement quantification that does $not$ rely on synchronized reference frames. Counterintuitively, measurements in random and unknown bases can be used to establish just how entangled a quantum state is. This strategy may prove useful in complex quantum communication networks, where establishing a common reference frame (measurement basis) is impractical or impossible.

Spin Hall nano-oscillators can generate radio-frequency output from direct-current input, and being planar structures with well defined geometry leaves them suitable for integration into microwave technologies. Control over output amplitude and frequency can be achieved by tuning magnetic field and direct current, but little is known about how these oscillators respond to input that changes rapidly, on the nanosecond time scale. This study shows that input current pulses just a few ns in duration are sufficient to generate rf output. Also, pulsing current and external rf inputs further improves the frequency and amplitude stability of the magnetization oscillations.

The authors address a critical roadblock in the development of topological qubits: charge impurities within semiconductor-superconductor hybrid structures. Majorana zero modes may occur in such nanowires and hold promise as the building blocks of topological quantum computers, but disorder in the system can destroy these modes. This work shows that charge impurities within the semiconductor lead to serious complications, with direct implications for the development of Majorana-based qubits. Upper limits are found for the level of charge-impurity density that still allows Majorana zero modes to emerge, providing clear direction for what needs to be done to achieve real-world progress.

Although it originated in quantum physics, the concept of $non-Hermiticity$ (particularly involving a Hamiltonian with $balanced$ gain and loss, and thus $PT$ symmetry and an exceptional point in frequency space) can also play a key role in classical systems, including those in acoustics. By incorporating suitably engineered gain or loss media, both cavity and scattering acoustic systems can produce a series of intriguing wave phenomena, with prospects for application in the design of innovative functional devices. This review aims to introduce the pedagogical models and recent achievements in this field, in the hope of being useful to a diverse audience.