A major campaign of domino-toppling simulations yields new insights into the effects of friction.

Time-dependent eigenstates of Hamiltonians offer a large degree of tunability, which can be leveraged to operate single- and two-qubit gates so that they stay dynamically protected from noise. However, the usual analytical techniques for describing these gates are limited for systems subject to drives of different frequencies. Thus the authors generalize the Floquet approach to the understanding of such systems, and provide protocols to robustly control and measure these complex systems.

For real-world quantum communication, how perfect does a system actually need to be? Here researchers propose a private dense-coding framework using a general preshared quantum state, for quantum secure direct communication that unifies a large number of protocols aimed at secure classical communication using quantum resources. This study provides a detailed performance analysis for the framework in both the asymptotic and nonasymptotic cases, and a better upper bound on information leakage in the finite-length setting. For practical application, the authors also propose an efficient method for implementation, under certain assumptions.

The rise of artificial intelligence has led to an explosion in demand for computing power—demand that soon will be insatiable using conventional CMOS-based computing hardware. Thus there is a worldwide quest for unconventional hardware that can replace or complement CMOS-based gear. This study contributes to that quest simulations of how reconfigurable logic can be realized in disordered dopant networks in a semiconductor. This paper reveals the operating principles, based on variable-range hopping of charges between randomly located dopants, that underlie the performance of complex classification tasks by these networks.

The experimental realization of knotted fields at macroscopic length scales has been achieved in the past decade, and recently applications based on knots of optical vortices have been demonstrated in information storage and transmission. Wider applicability and the experimental realization of theoretical proposals have been held back due to the relatively large size of such knots. This study shows how to generate optical-vortex knots at the scale of an optical wavelength, which is an important milestone and removes the previous limitations. The authors further observe a change in topology, from a knot to two separated loops.

In the burgeoning field of quantum secure communication, the “chipization” and integration of quantum key distribution (QKD) systems is a prime topic. Here the authors demonstrate a prototype of an integrated optoelectronic QKD transmitter: a photonics chip that integrates the essential encoding components for the decoy-state BB84 protocol, plus electronics chips that integrate the dedicated driving circuits. Experiments at a repetition rate of 312.5 MHz verify the system’s performance. This work takes a key step toward system-in-package QKD applications.

Tunnel coupling is a key parameter in coupled semiconductor quantum dots, and is a crucial ingredient in various device applications, such as exchange gates and spin shuttling in quantum information processing. A widely used charge-sensing technique to extract the tunnel coupling of a double quantum dot accounts for only the ground orbital state in each dot, but the authors show that in a Si double dot, valley-orbit coupling must be included in the analysis. With their more complete model, one can not only extract the $intravalley$ (ground-state) tunnel coupling more accurately, but also obtain information on $intervalley$ (ground-to-excited-state) tunnel coupling.

Artificial spin ices (ASIs) are arrays of Isinglike magnetic nanoislands that are of interest for magnetically reconfigurable computing architectures. Many ASI studies use the metal permalloy, which facilitates geometry-driven studies but leaves material-driven factors largely unexplored. Here the authors study nanoisland magnetic states in ASIs fabricated from the complex oxide La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$ (LSMO), and find that both Ising and vortex states can be stabilized through a careful balance of inter- and intraisland energetics enabled by LSMO’s magnetic parameters. These tunable magnetic states provide opportunities to introduce exotic phases into ASI arrays.

Metasurfaces could have transformational impact on emerging applications, from smart antennas and 6G communication to the Internet of Things and wireless power transfer, thanks to their ultracompact dimensions and tailored designs. To fully realize this potential, metasurfaces that can implement different functionalities and dynamically switch between them are desired. This study presents a multifunctional microwave metasurface architecture that incorporates electronic components within the unit cell to exert control over the metasurface’s response. Bridging applied physics and device engineering, this work is a concrete step toward readily deployable and versatile metasurface technology.

Qubit calibration and characterization are important for attaining high-fidelity gates in quantum computing, but require a significant amount of time, which limits a device’s ability to run useful quantum circuits. This study uses restless measurement, in which the qubits are never reset, to speed up characterization and calibration tasks. The authors also show how quantum process tomography may be performed in a restless setting. This approach reduces the footprint of characterization and calibration on quantum processors by quickly and faithfully executing the corresponding circuits.

Controlling superconductivity locally and for nonvolatile effect is important for constructing sketchable nanoscale superconducting electronic devices, but few superconducting systems are suitable. This study uses an electrically biased scanning probe to exert local and nonvolatile control over the recently discovered LaAlO${}_3$/KTaO${}_3$ interfacial superconductivity. It presents a system in which rewritable superconducting, normal, and insulating states can be flexibly defined in the same material, on demand.

The authors present a phenomenological model of the $longitudinal$ relaxation processes of magnetic domain walls in ferromagnetic films featuring the Dzyaloshinskii-Moriya interaction. This model enables predictions in quantitative agreement with experiments. In contrast to expectations from state-of-the-art theories, for ultrathin films the contribution from longitudinal relaxation is comparable to or even $stronger$ $than$ $any$ $other$ $mechanism$, including spin pumping. This effect is generic and valid for any noncollinear texture, including the domain walls and skyrmions that are technologically relevant for logic and memory devices.

The phenomenon of spin hydrodynamic generation (SHDG) unites research in spintronics and fluid dynamics. Revealing the physical properties of SHDG is necessary to strengthen the connection between these two fields, and to expand the applicability of SHDG. Here the authors measure SHDG in liquid gallium, and find that SHDG shows negative dependence on the spin-orbit interaction and no remarkable dependence on the Newtonian viscosity. This study lays the groundwork for applications in microfluidics and manipulation of SHDG.

Vertical tunneling transistors are of interest in the development of next-generation electronics. However, due to nonideal metal-semiconductor interfaces, the majority tunneling carrier type and device polarity are largely fixed, posing a key limitation for practical application. The authors demonstrate complementary tunneling behaviors in vertical heterostructures using ultrathin BN as a tunneling barrier and damage-free van der Waals metal as the top contact, in which the majority carrier type can be switched from electrons to holes by a bias voltage. This work provides proof of principle and comprehensive understanding of the tunneling mechanism in these high-performance devices.

In the search for axion dark matter, superconducting rf technology is important for fabricating microwave cavities with high $Q$ factors, but the presence of a strong external magnetic field leads to technical difficulties. This study presents a polygonal design with tapes of high-temperature superconductor to realize a superconducting resonant cavity that shows no considerable degradation in magnetic fields up to 8 Tesla. This approach could impact engineering solutions to improve dark-matter detection and other research areas requiring low cavity loss in a strong magnetic field.

Time-dependent eigenstates of Hamiltonians offer a large degree of tunability, which can be leveraged to operate single- and two-qubit gates so that they stay dynamically protected from noise. However, the usual analytical techniques for describing these gates are limited for systems subject to drives of different frequencies. Thus the authors generalize the Floquet approach to the understanding of such systems, and provide protocols to robustly control and measure these complex systems.

For real-world quantum communication, how perfect does a system actually need to be? Here researchers propose a private dense-coding framework using a general preshared quantum state, for quantum secure direct communication that unifies a large number of protocols aimed at secure classical communication using quantum resources. This study provides a detailed performance analysis for the framework in both the asymptotic and nonasymptotic cases, and a better upper bound on information leakage in the finite-length setting. For practical application, the authors also propose an efficient method for implementation, under certain assumptions.

A major campaign of domino-toppling simulations yields new insights into the effects of friction.

The rise of artificial intelligence has led to an explosion in demand for computing power—demand that soon will be insatiable using conventional CMOS-based computing hardware. Thus there is a worldwide quest for unconventional hardware that can replace or complement CMOS-based gear. This study contributes to that quest simulations of how reconfigurable logic can be realized in disordered dopant networks in a semiconductor. This paper reveals the operating principles, based on variable-range hopping of charges between randomly located dopants, that underlie the performance of complex classification tasks by these networks.

The experimental realization of knotted fields at macroscopic length scales has been achieved in the past decade, and recently applications based on knots of optical vortices have been demonstrated in information storage and transmission. Wider applicability and the experimental realization of theoretical proposals have been held back due to the relatively large size of such knots. This study shows how to generate optical-vortex knots at the scale of an optical wavelength, which is an important milestone and removes the previous limitations. The authors further observe a change in topology, from a knot to two separated loops.

In the burgeoning field of quantum secure communication, the “chipization” and integration of quantum key distribution (QKD) systems is a prime topic. Here the authors demonstrate a prototype of an integrated optoelectronic QKD transmitter: a photonics chip that integrates the essential encoding components for the decoy-state BB84 protocol, plus electronics chips that integrate the dedicated driving circuits. Experiments at a repetition rate of 312.5 MHz verify the system’s performance. This work takes a key step toward system-in-package QKD applications.

Tunnel coupling is a key parameter in coupled semiconductor quantum dots, and is a crucial ingredient in various device applications, such as exchange gates and spin shuttling in quantum information processing. A widely used charge-sensing technique to extract the tunnel coupling of a double quantum dot accounts for only the ground orbital state in each dot, but the authors show that in a Si double dot, valley-orbit coupling must be included in the analysis. With their more complete model, one can not only extract the $intravalley$ (ground-state) tunnel coupling more accurately, but also obtain information on $intervalley$ (ground-to-excited-state) tunnel coupling.

Artificial spin ices (ASIs) are arrays of Isinglike magnetic nanoislands that are of interest for magnetically reconfigurable computing architectures. Many ASI studies use the metal permalloy, which facilitates geometry-driven studies but leaves material-driven factors largely unexplored. Here the authors study nanoisland magnetic states in ASIs fabricated from the complex oxide La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$ (LSMO), and find that both Ising and vortex states can be stabilized through a careful balance of inter- and intraisland energetics enabled by LSMO’s magnetic parameters. These tunable magnetic states provide opportunities to introduce exotic phases into ASI arrays.

Metasurfaces could have transformational impact on emerging applications, from smart antennas and 6G communication to the Internet of Things and wireless power transfer, thanks to their ultracompact dimensions and tailored designs. To fully realize this potential, metasurfaces that can implement different functionalities and dynamically switch between them are desired. This study presents a multifunctional microwave metasurface architecture that incorporates electronic components within the unit cell to exert control over the metasurface’s response. Bridging applied physics and device engineering, this work is a concrete step toward readily deployable and versatile metasurface technology.

Qubit calibration and characterization are important for attaining high-fidelity gates in quantum computing, but require a significant amount of time, which limits a device’s ability to run useful quantum circuits. This study uses restless measurement, in which the qubits are never reset, to speed up characterization and calibration tasks. The authors also show how quantum process tomography may be performed in a restless setting. This approach reduces the footprint of characterization and calibration on quantum processors by quickly and faithfully executing the corresponding circuits.