In quantum information processing, using positive operator–valued measurements (POVMs) enables the design of general measurement schemes and efficient estimation methods with fixed circuits, but the CNOT-gate count during compilation becomes a bottleneck. This study shows that any single-qubit minimal informationally complete POVM (IC POVM) can be realized with at most two CNOT gates—and a symmetric case (SIC POVM) requires only one. This is achieved by virtually inserting gates to adjust unrelated parameters in the compilation circuit. The authors also provide a concise compilation circuit for single-qubit SIC POVMs, paving the way for practical application.

For spintronic circuits based on the magnetic racetrack concept, soft patterning by dipolar and exchange interactions is an alternative to lithography, with the added advantage of full reconfigurability. In this study, parallel-stripe domain patterns in a hard magnetic layer with weak perpendicular anisotropy create linear paths that guide the propagation of domain walls in an adjacent soft magnetic layer. An exchange-bias field remembers the last saturated state, due to the localized magnetic spring at the interface. These results provide a basis for reconfigurable domain-wall racetracks in which the propagation direction can be controlled by magnetic history and applied fields.

Following the revision of the International System of Units in 2019, the unit of electrical resistance (the familiar ohm) is defined in terms of Planck’s constant $h$ and the elementary charge $e$. The primary standard for the ohm is based on GaAs quantum Hall resistance devices operating under extreme conditions, which hinders application outside national metrology institutes. This study presents , graphene-based quantum Hall resistance standards that can be employed under relaxed conditions for practical metrology, supplanting the GaAs standard. These graphene devices can lead to broader dissemination of primary resistance standards in calibration laboratories and industry.

Quantum transport straintronics (QTS) aims to engineer quantum coherent charge transport using mechanical deformations in one- and two-dimensional materials. Progress here is limited because existing theories are idealized, while experiments face challenges such as edge effects. This study shows that single-wall carbon nanotubes (SWCNTs) are ideal systems for future QTS experiments, due to their perfect periodic boundary conditions. The authors present a comprehensive model of QTS in SWCNT transistors to simulate realistic experiments, with transport calculations displaying a rich set of strain-tunable quantum interferences.

Low-loss deposited dielectrics are beneficial for improving superconducting circuits used in astronomy. At cryogenic temperature and low electric field, in the microwave band the dielectric loss is known to be dominated by two-level systems, but the origin of loss in the millimeter-submillimeter band is not understood. Here researchers measure the loss of $a$-SiC:H films from 0.27 to100 THz, using superconducting microstrip resonators and Fourier-transform spectroscopy. The data are explained well by a Maxwell-Helmholtz-Drude dispersion model, suggesting that vibrational modes dominate the loss in this material above 200 GHz.

The Global Positioning System (GPS) provides uninterrupted position and timing data across the globe with a precision of up to 40 ns, but is insufficient for advanced applications such as quantum communication, and is susceptible to jamming and spoofing attacks. This article introduces a protocol for synchronizing clocks using a constellation of satellites that relies on the exchange of entangled photons. Simulation shows that 50 low-Earth-orbit satellites bearing off-the-shelf atomic clocks can distribute time globally with a precision that is 2 to 4 orders of magnitude higher than that of GPS. Additionally, the use of entangled photons provides an extra layer of quantum security.

Electron-hole recombination is a key process in semiconductor physics, though its role in the electrical response of devices such as halide perovskite solar cells remains unclear, due to a lack of suitable equivalent-circuit models. Here such a model for recombination processes, when integrated within a transmission line, allows the derivation of a device model that is analytically equivalent to the drift-diffusion equations. Elucidating the polarization processes that set the characteristic time scales of changes in recombination impedance, this model and its analytic approximations facilitate the optimization of devices for energy conversion, optoelectronics, and photoelectrochemistry.

Entanglement generation using the single-photon protocol is of interest for quantum networks, for its reduced sensitivity to photon losses. This protocol requires a stable relative optical phase on the optical link between network nodes. The authors present a phase-synchronization scheme that enables scalable entanglement generation over metropolitan distances, in a robust and extendable infrastructure. Their results show the feasibility of the single-click heralding protocol at long distances, and the approach can also be used with other types of node hardware, for near-term exploration of large-scale quantum networks.

Elastocaloric cooling holds considerable promise as a compact, quick alternative to standard cryogenic refrigeration, though its practical implementation still requires considerable research on candidate materials and appropriate techniques for applying large, rapid strains at low temperatures. In this study a load-unload approach is used to induce substantial strains in a candidate cryogenic elastocaloric working material, TmVO${}_4$, at low temperatures. Employing this technique, the authors observe a giant elastocaloric response, cooling the material by 2.3 K at a bath temperature of 5 K. These results provide a starting point for practical elastocaloric cooling in the subkelvin regime.

The sensitivity of ultracold-atom sensors has great potential for on-board applications, but achieving this precision outside the laboratory requires a robust, compact atom source. This work presents a hybrid atom chip that combines two techniques to simplify the cold-atom source: optical gratings for single-beam laser cooling and conductive microcircuits for tight magnetic confinement. This hybrid configuration also achieves Bose-Einstein condensation. This research paves the way for integrating more advanced features into atomic chips with applications in atomic interferometry and atomtronics.

Magnetomechanical stimulation (MMS) of cells has a huge potential in biomedicine, using accurately controlled magnetic forces on targeted cells for applications like cancer therapy, insulin regulation, or neurodegenerative diseases. This perspective suggests further directions of research and experiments in this interdisciplinary field that combines physics, biology (especially mechanobiology), and medicine to optimize magnetic tools, deepen understanding of cellular responses, and assess the safety and efficacy of MMS in in vivo models and humans. MMS holds promise but progress is still needed to realize its full potential in real-world medical applications.

The sensitivity of ultracold-atom sensors has great potential for on-board applications, but achieving this precision outside the laboratory requires a robust, compact atom source. This work presents a hybrid atom chip that combines two techniques to simplify the cold-atom source: optical gratings for single-beam laser cooling and conductive microcircuits for tight magnetic confinement. This hybrid configuration also achieves Bose-Einstein condensation. This research paves the way for integrating more advanced features into atomic chips with applications in atomic interferometry and atomtronics.

Ferroelectric domain imaging is important for ferroelectric and multiferroic applications but is being held back by the paucity of high-spatial-resolution microscopy techniques. This study uses linear dichroic soft-X-ray ptychography at the O K-edge to image the ferroelectric domains in BiFeO${}_3$ and compare them with the antiferromagnetic contribution obtained at the Fe L-edge. The hybridization of O 2p states with Fe 3d orbitals is found to be important for the observability of the X-ray linear dichroism. This approach will impact the study of ferroic contributions in multiferroics and the imaging of ferroelectrics containing elements inaccessible in the soft-X-ray energy regime.

Photon-absorption-based quantum circuit refrigeration is crucial to developing superconducting quantum computers, particularly for initializing qubits. However, precise and rapid measurement of residual photons in the circuit immediately after absorption has been a significant technical challenge. This study employs the ac Stark shift of superconducting qubits to detect sub-photon-level energies in the circuit, confirming the effectiveness of the fast refrigeration even in the quantum regime. These results will facilitate the development of more efficient quantum refrigeration devices and faster, high-fidelity qubit initialization.

Magnons (magnetic quasiparticles) coupled to photons are referred to as magnon polaritons (MPs). Ultrastrongly coupled and directionally nonreciprocal MPs at room temperature would be important for spintronic hybrid quantum systems, but that combination of properties has not yet been observed. This study uses metamaterials without time-reversal or space-inversion symmetries to make progress on the problem, and its results will impact the engineering of synthetic gauge fields, as well as quasiparticle “chemistry” and hybrid quantum systems.

As opposed to feedback, feedforward methods bring new opportunities to suppress high-frequency laser phase noise, but their performance is more susceptible to environmental perturbations, hindering broad application. Tackling the key factors for long-term stability of feedforward based on Pound-Drever-Hall (PDH) detection, the authors construct a compact circuit to adaptively control feedforward gain in response to power variations of cavity transmission. This design achieves robust suppression beyond 40 dB for megahertz noise frequencies. The compact scheme may promote the general use of reliable PDH feedforward in simple, inexpensive lasers for precision quantum control and metrology.

In quantum information processing, using positive operator–valued measurements (POVMs) enables the design of general measurement schemes and efficient estimation methods with fixed circuits, but the CNOT-gate count during compilation becomes a bottleneck. This study shows that any single-qubit minimal informationally complete POVM (IC POVM) can be realized with at most two CNOT gates—and a symmetric case (SIC POVM) requires only one. This is achieved by virtually inserting gates to adjust unrelated parameters in the compilation circuit. The authors also provide a concise compilation circuit for single-qubit SIC POVMs, paving the way for practical application.

For spintronic circuits based on the magnetic racetrack concept, soft patterning by dipolar and exchange interactions is an alternative to lithography, with the added advantage of full reconfigurability. In this study, parallel-stripe domain patterns in a hard magnetic layer with weak perpendicular anisotropy create linear paths that guide the propagation of domain walls in an adjacent soft magnetic layer. An exchange-bias field remembers the last saturated state, due to the localized magnetic spring at the interface. These results provide a basis for reconfigurable domain-wall racetracks in which the propagation direction can be controlled by magnetic history and applied fields.

Following the revision of the International System of Units in 2019, the unit of electrical resistance (the familiar ohm) is defined in terms of Planck’s constant $h$ and the elementary charge $e$. The primary standard for the ohm is based on GaAs quantum Hall resistance devices operating under extreme conditions, which hinders application outside national metrology institutes. This study presents , graphene-based quantum Hall resistance standards that can be employed under relaxed conditions for practical metrology, supplanting the GaAs standard. These graphene devices can lead to broader dissemination of primary resistance standards in calibration laboratories and industry.

Quantum transport straintronics (QTS) aims to engineer quantum coherent charge transport using mechanical deformations in one- and two-dimensional materials. Progress here is limited because existing theories are idealized, while experiments face challenges such as edge effects. This study shows that single-wall carbon nanotubes (SWCNTs) are ideal systems for future QTS experiments, due to their perfect periodic boundary conditions. The authors present a comprehensive model of QTS in SWCNT transistors to simulate realistic experiments, with transport calculations displaying a rich set of strain-tunable quantum interferences.

Low-loss deposited dielectrics are beneficial for improving superconducting circuits used in astronomy. At cryogenic temperature and low electric field, in the microwave band the dielectric loss is known to be dominated by two-level systems, but the origin of loss in the millimeter-submillimeter band is not understood. Here researchers measure the loss of $a$-SiC:H films from 0.27 to100 THz, using superconducting microstrip resonators and Fourier-transform spectroscopy. The data are explained well by a Maxwell-Helmholtz-Drude dispersion model, suggesting that vibrational modes dominate the loss in this material above 200 GHz.

The Global Positioning System (GPS) provides uninterrupted position and timing data across the globe with a precision of up to 40 ns, but is insufficient for advanced applications such as quantum communication, and is susceptible to jamming and spoofing attacks. This article introduces a protocol for synchronizing clocks using a constellation of satellites that relies on the exchange of entangled photons. Simulation shows that 50 low-Earth-orbit satellites bearing off-the-shelf atomic clocks can distribute time globally with a precision that is 2 to 4 orders of magnitude higher than that of GPS. Additionally, the use of entangled photons provides an extra layer of quantum security.

Electron-hole recombination is a key process in semiconductor physics, though its role in the electrical response of devices such as halide perovskite solar cells remains unclear, due to a lack of suitable equivalent-circuit models. Here such a model for recombination processes, when integrated within a transmission line, allows the derivation of a device model that is analytically equivalent to the drift-diffusion equations. Elucidating the polarization processes that set the characteristic time scales of changes in recombination impedance, this model and its analytic approximations facilitate the optimization of devices for energy conversion, optoelectronics, and photoelectrochemistry.

Entanglement generation using the single-photon protocol is of interest for quantum networks, for its reduced sensitivity to photon losses. This protocol requires a stable relative optical phase on the optical link between network nodes. The authors present a phase-synchronization scheme that enables scalable entanglement generation over metropolitan distances, in a robust and extendable infrastructure. Their results show the feasibility of the single-click heralding protocol at long distances, and the approach can also be used with other types of node hardware, for near-term exploration of large-scale quantum networks.

Elastocaloric cooling holds considerable promise as a compact, quick alternative to standard cryogenic refrigeration, though its practical implementation still requires considerable research on candidate materials and appropriate techniques for applying large, rapid strains at low temperatures. In this study a load-unload approach is used to induce substantial strains in a candidate cryogenic elastocaloric working material, TmVO${}_4$, at low temperatures. Employing this technique, the authors observe a giant elastocaloric response, cooling the material by 2.3 K at a bath temperature of 5 K. These results provide a starting point for practical elastocaloric cooling in the subkelvin regime.