In this work we analyze the implementation of a control-phase gate through the resonance between the $\mid 11⟩$ and $\mid 20⟩$ states of two statically coupled transmons. We find that there are many different controls for the transmon frequency that implement the same gate with fidelities around $99.8\mathrm{\%}$ ($T_1=T_2=17\mu \mathrm{s}$) and $99.99\mathrm{\%}$ ($T_1=T_2=300\mu \mathrm{s}$) within a time that approaches the theoretical limit. All controls can be brought to this accuracy by calibrating the waiting time and the destination frequency near the $\mid 11⟩-\mid 20⟩$ resonance. However, some controls, such as those based on the theory of dynamical invariants, are particularly attractive due to reduced leakage, robustness against decoherence, and their limited bandwidth.

We realize soft topological mechanical metamaterials with pronounced polar elastic responses (i.e., softer on one edge than the other) in both the quasistatic and dynamic regimes. Numerical simulations and experimental results confirm the presence of directional dependence in metamaterial response at low and high strain rates, despite the use of lossy elastomer as bulk media. The metamaterials exhibit means to tailor the location of topologically protected uniaxial mechanical stiffnesses by virtue of both loading orientation and geometric changes to the lattice architecture. High-speed video recordings show strong topologically protected asymmetric wave propagation for the soft metamaterials subjected to impact. The results indicate a class of metamaterial architectures possessing polar elastic behavior and confirm the persistence of the response in lossy media.

The extension of spin coherence times is a crucial issue for quantum information and quantum sensing. In solid-state systems, suppressing noise through various techniques has been demonstrated. On the other hand, an electrical control for suppression is important toward individual controls of on-chip quantum-information devices. Here, we show electrical control for extension of the spin coherence times of 40-nm-deep ion-implanted single-nitrogen-vacancy center spins in diamond by suppressing magnetic noise. We apply 120 V dc across two contacts spaced by 10 μm. The spin coherence times, estimated from a free-induction decay and a Hahn-echo decay, are increased up to about 10 times (reaching 10 μs) and 1.4 times (reaching 150 μs), respectively. From the quantitative analysis, the dominant decoherence source, depending on the applied static electric field, is elucidated. Electrical control for extension can deliver a sensitivity enhancement to the dc sensing of temperature, pressure, and electric (but not magnetic) fields, opening up an alternative technique in solid-state quantum-information devices.

Neural networks based on machine learning can interpolate well within the training dataset, but their ability to extrapolate is severely limited by fundamental issues such as the bias-variance trade-off. Here we introduce the concept of an operator parameter space consisting of physical entities encoded with Maxwell’s equations to improve the networks’ capability to generalize beyond their training set. We illustrate the idea with photonic crystals, and show that the network trained with operator parameters yields remarkably accurate predictions of the topological transitions both within and beyond the training physical space. Such concepts can be generalized to higher-dimensional wave structures by choosing the appropriate operator parameters.

The shrinking of field-effect transistors (FETs) is in great demand for next-generation integrated circuits. However, traditional silicon FETs are reaching the scaling limits, and it is therefore urgent to explore alternative paradigms. Two-dimensional (2D) materials attract great research enthusiasm, owing to their abilities to suppress short-channel effects. Herein, we evaluate the electronic properties and device performance of ultrascaled 2D ${\mathrm{Sn}\mathrm{S}}_2$ metal-oxide-semiconductor FETs (MOSFETs) via ab initio simulations. Specifically, the $I_{\mathrm{on}}$ value of the 5.5 nm monolayer ${\mathrm{Sn}\mathrm{S}}_2$ n-MOSFETs is ultrahigh, up to 3400 µA/µm, as a result of the small effective masses of the conduction-band minimum of monolayer ${\mathrm{Sn}\mathrm{S}}_2$. Until the channel length is scaled down to 4 nm, the MOSFETs can fulfill the standards of $I_{\mathrm{on}}$, delay time, and power dissipation product of the International Roadmap for Devices and Systems (IRDS) 2018 goals for high-performance devices. Moreover, the 5.5 nm monolayer ${\mathrm{Sn}\mathrm{S}}_2$ n-MOSFETs can also fulfill the IRDS 2018 requirements for the 2028 horizon for low-power applications. This work demonstrates that monolayer ${\mathrm{Sn}\mathrm{S}}_2$ is a favorable channel material for future competitive ultrascaled devices.

Personal radiative thermal management using photonic smart textiles has become a center of attention due to its potential to facilitate thermal comfort, and to decrease the energy cost for heating and cooling. Here, we provide an approach for a dynamic transmittance switch textile (DTST): a dynamic, passive, radiative thermal regulating fabric that controls the infrared (IR) transmission by adapting to the ambient temperature and humidity. The DTST is constituted from metal-coated monofilaments and stimuli-responsive polymer actuator beads, in this way benefiting from multiple IR photonic effects to strongly control the wide-band transmission of thermal radiation and to provide for a sharp, dynamic response. This design shows a wide dynamic ambient setpoint temperature window of approximately $16{}^{\circ }\mathrm{C}$, meaning that the wearer is comfortable between 9.5 and $25.7{}^{\circ }\mathrm{C}$, wider than any theoretically reported or fabricated switchable fabric. This performance indicates a polyvalent user comfort and an important energy saving potential for residential and office buildings.

Photon-number-resolving detectors (PNRDs) play pivotal roles in many quantum-photonic applications; and intrinsic and multiplexed PNRDs have been reported previously. However, for intrinsic PNRDs, the maximum resolvable photon number is limited to a few photons; for the multiplexed PNRDs, the fidelity generally decreases when the to-be-resolved photon number becomes large. Here, to resolve more photons with high fidelity, we report on combined PNRDs, based on a spatial multiplexing configuration of multiple elements, each capable of resolving a few photons. After setting up a model and calculating the fidelity, we propose a possible physical system to realize the combined PNRDs. The proposed detectors are based on the superconducting nanowire multiphoton detectors integrated with current reservoirs that we recently reported, but are designed and configured into PNRDs. Specifically, information about the detected photon numbers is stored in the format of the supercurrent in the current reservoir and then readout by an integrated yTron. We present in detail the operating principle and show a design that can resolve up to 11 photons with high fidelity.

The electronic properties of van der Waals heterostructures composed of ${\mathrm{Mo}\mathrm{S}}_2$ and ${\mathrm{WS}}_2$ under a perpendicular electric field are studied in terms of field strength, electron doping concentration, and interlayer stacking arrangement based on the density-functional theory. The calculation results show that accumulated carrier distribution can be controlled by tuning the field direction, field strength, and doping concentration. The electron is localized on the ${\mathrm{Mo}\mathrm{S}}_2$ layer on the positively charged electrode side under a strong positive field with a low doping concentration, whereas they are extended throughout both the ${\mathrm{Mo}\mathrm{S}}_2$ and ${\mathrm{WS}}_2$ layers under a strong negative field. Stacking misorientation between the layers further enhances the electron localization under a positive field and delocalization under a strong negative field. The stacking arrangement and electric field allow additional tuning of the electronic properties of van der Waals heterostructures.

We report a weighing metrology experiment of a single silica microsphere optically trapped and immersed in air. Based on fluctuations about thermal equilibrium, three different mass measurements are investigated, each arising from one of two principle methods. The first method is based on spectral analysis and enables simultaneous extraction of various system parameters. Additionally, the spectral method yields a mass measurement with systematic relative uncertainty of 3.0% in 3 s and statistical relative uncertainty of 0.9% across several trapping laser powers. Parameter values learned from the spectral method serve as input, or a calibration step, for the second method based on the equipartition theorem. The equipartition method gives two additional mass measurements with systematic and statistical relative uncertainties slightly larger than those obtained in the spectral method, but over a time interval 10 times shorter. Our mass estimates, which are obtained in a scenario of strong environmental coupling, have uncertainties comparable to ones obtained in force-driven metrology experiments with nanospheres in vacuum. Moreover, knowing the microsphere’s mass accurately and precisely will enable air-based sensing applications.

Multimode entanglement is an essential resource for quantum information in continuous-variable systems. Light-based quantum technologies will arguably not be built upon table-top bulk setups, but will presumably rather resort to integrated optics. Sequential bulk opticslike proposals based on cascaded integrated interferometers are not scalable with the current state-of-the-art low-loss materials used for continuous variables. We analyze the multimode continuous-variable entanglement capabilities of a compact currently available integrated bulk-optics analog: the array of nonlinear waveguides. We theoretically demonstrate that this simple and compact structure, together with a reconfigurable input pump distribution and multimode coherent detection of the output modes, is a versatile entanglement synthesizer in the spatial domain. We exhibit this versatility through analytical and numerically optimized multimode squeezing, entanglement, and cluster-state generation in different encodings. Our results re-establish spatial encoding as a contender in the game of continuous-variable quantum information processing.

Propagation and relaxation of nonequilibrium quasiparticles in superconductors are fundamental for functioning of numerous nanoscale devices, enabling operation of some of them, and limiting the performance of others. The quasiparticles heated above lattice temperature may relax locally via phonon or photon-emission channels, or diffuse over appreciable distances in a nanostructure altering the functionality of their remote components. Tracing quasiparticles experimentally in real-time domain has remained a challenging task owing to their rapid dynamics. With electronic nanothermometry, based on probing of the temperature-dependent switching current of a superconducting nanobridge, we monitor heat pulse carried by a flux of nonequilibrium quasiparticles as it passes by our detector with a noise-equivalent temperature of 10 $\mathrm{mK}/\sqrt{N}$, where $N$ is the number of pulses probing the bridge (typically $N=10000$), and temporal resolution of a single nanosecond. The measurement provides the picture of quasiparticle diffusion in a superconducting aluminum strip and direct determination of the diffusion constant $D$ equal to 100 ${\mathrm{cm}}^2/$s with no energy dependence visible.

Manipulating thermal conductivity through nanoengineering is of critical importance to advance technologies, such as soft robotics, artificial skin, wearable electronics, batteries, thermal insulation, and thermoelectrics. Here, by examining amorphous polymers, including polystyrene, polypropylene, polyethylene, and ethylene vinyl alcohol, using molecular dynamics simulations, we find that the thermal conductivities of amorphous polymers can be reduced below their amorphous limit by size effects. Size-dependent thermal transport in amorphous materials is decomposed into crystalline, crystalline-to-amorphous, and amorphous regimes. In the amorphous regime, the mean free path of propagating heat carriers can range from tens of nanometers to more than 100 nm, contributing 16%–36% of the total thermal conductivity. A two-channel model that combines no size effect (i.e., difusons and locons) and size effect (i.e., propagons) is proposed to account for size-dependent thermal conductivity. We also find that the presence of charged molecules in polymers can significantly affect the thermal conductivity and its size effects due to electrostatic interactions. This work provides insights into the thermal conductivity of amorphous polymers that will have a broad impact on the nano- and chemical engineering of polymers for various energy-related applications.

Electrical excitation of surface plasmons via metal-insulator-metal tunneling junctions ($M$-$I$-$M$ TJs) has recently been demonstrated to have experimental conversion efficiencies of 1% [W. Du et al. Nat. Photonics 11, 623 (2017)], 5–6 orders of magnitude higher than theoretically predicted by Parzefall and Novotny [ACS Photonics 5, 4195 (2018)]. In this work we resolve this discrepancy between theory and experiment, and report a rigorous analytical and experimental study on the role of surface roughness in the near-field coupling of the initially excited $M$-$I$-$M$ TJ cavity surface plasmon polariton ($M$-$I$-$M$ SPP) to the daughter radiative and nonradiative modes. We find that varying the roughness profile of the $M$-$I$-$M$ TJ significantly (which is determined with atomic force microscopy and cross-section scanning transmission electron microscopy) improves the near-field outcoupling efficiency for two reasons: the effective thickness of the electrodes reduces with increasing roughness, and roughness provides momentum matching for mode overlap. The role of surface roughness in near-field outcoupling is analysed quantitatively by incorporating a conformal random roughness profile in the finite-element electromagnetic modeling of a plasmonically active $M$-$I$-$M$ TJ. We show that the outcoupling efficiency can be enhanced up to 15% for the $M$-$I$-$M$ SPP coupling to daughter modes, and demonstrate an overall electron-to-plasmon conversion efficiency of 1.5% (based on an inelastic tunneling efficiently of 10%), supporting recent experimental findings. This work provides an explanation for the high observed experimental efficiencies and bridges the knowledge gap between prior theoretical works and experiments by including the role of roughness in the electromagnetic near-field coupling in $M$-$I$-$M$ TJs.

Nonlinear materials are of great technological interest for the realization of nanophotonic devices able to control and manipulate light. These properties can be specifically engineered by exploiting the surface plasmon resonance of plasmonic nanocomposites, in proximity of which nonlinear absorption and refraction are largely enhanced. An exploration of the spectral, irradiance, and host material dependence of the nonlinear parameters is important to be able to gain a thorough understanding of the nonlinear response. In the present work, we investigate the nonlinear optical response of $\mathrm{Au}$ and $\mathrm{Ag}$ nanoparticles embedded in sapphire by a spectral $z$-scan characterization across the localized surface plasmon band of the samples. We also present a comparison of the results obtained for $\mathrm{Au}$ nanoparticles embedded both in silica and in sapphire, produced under equivalent conditions, to test the influence of the host material. We theoretically describe the spectral trends of both the nonlinear absorption coefficient and nonlinear refractive index by implementing a three-level model, which provides important insights into the main physical parameters controlling the observed spectral features, and the possibility of ab initio composite designs with tailored properties.

Dynamic nuclear polarization (DNP) is well recognized as being important in spintronics and quantum-information processing. DNP gives rise to high nuclear spin polarization that not only can prolong electron-spin lifetime by generating an Overhauser field (OHF), but also has fertilized the idea to explore nuclear spin qubits. In strained quantum-dot structures (QDSs), a nuclear spin is coupled to a strain field via its quadrupole moment. It has been shown that such nuclear quadrupole interaction (NQI) can be used to achieve appreciable DNP and hence electron-spin polarization. Here, we uncover magneto-optical anomalies from a series of laterally arranged $(\mathrm{In},\mathrm{Ga})\mathrm{As}$ QDSs that arise from the NQI and DNP in these nanostructures. We find that the principal axis of NQI in symmetry-lowered QDSs significantly deviates from the growth direction, resulting in tilting of OHF with an angle exceeding 37°. The resulting transverse component of OHF is probed with respect to the crystallographic orientations and its influence on the DNP and ensemble spin dephasing is analyzed. We show that a high-symmetry electronic confinement potential for excitons does not guarantee a high-symmetry NQI for nuclei within the same nano-object, thereby calling for correlated optimization in the symmetry of the electronic confinement potential and that of the nuclear spin bath. Our results underline the role of oblique NQI in electron-spin decoherence and depolarization, which has so far largely been overlooked. This work thus sheds light on design rules for engineering the electronic and spin landscape of QDSs for better performance of DNP desirable for applications in spintronics and quantum computation.

In this paper, we describe the vortex dynamics under a high-amplitude microwave drive and its effect on the surface resistance of superconductors. The vortex surface resistance is calculated with a Monte Carlo approach, where the vortex equation of motion is solved for a collection of vortex flux lines, each oscillating within a random pinning landscape. This approach is capable of providing a detailed description of the microscopic vortex dynamics and in turn important insights into the microwave-field-amplitude dependence of the vortex surface resistance. The numerical simulations are compared against experimental data of vortex surface resistance at high microwave amplitude measured by means of bulk niobium superconducting radio-frequency cavities operating at 1.3 GHz. The good qualitative agreement of the simulations and experiments suggests that the nonlinear dependence of the trapped-flux surface resistance with the microwave field amplitude is generated by progressive microwave depinning and vortex jumps.

Resonant excitation of solid-state quantum emitters enables coherent control of quantum states and generation of coherent single photons, which are required for scalable quantum-photonics applications. However, these systems can often decay to one or more intermediate dark states or spectrally jump, resulting in the lack of photons on resonance. Here we present an optical co-excitation scheme that uses a weak nonresonant laser to reduce transitions to a dark state and amplify the photoluminescence from quantum emitters in hexagonal boron nitride (h-BN). Using a two-laser repumping scheme, we achieve optically stable resonance fluorescence of h-BN emitters and an overall increase of on time of an order of magnitude compared with only resonant excitation. Our results are important for the deployment of atomlike defects in h-BN as reliable building blocks for quantum-photonics applications.

We use microfocus Brillouin light scattering spectroscopy to study the effects of spin-orbit torque on thermal spin waves in almost angular momentum compensated ferrimagnetic $\mathrm{Co}$-$\mathrm{Gd}$ alloy films. The spin-orbit torque is produced by the electric current flowing in the $\mathrm{Pt}$ layer adjacent to the $\mathrm{Co}$-$\mathrm{Gd}$ film. Both the ferromagnetic and the exchange modes are detected in our measurements. The intensity and the linewidth of the ferromagnetic mode are modified by the spin-orbit torque. In contrast, the properties of the exchange mode are unaffected by the spin-orbit torque. We also find that the frequencies and the linewidths of both modes are significantly modified by Joule heating, owing to the strong temperature dependence of the magnetic properties of $\mathrm{Co}$-$\mathrm{Gd}$ in the vicinity of the angular momentum compensation point. Our results provide insight into the mechanisms that can enable the implementation of subterahertz magnetic nano-oscillators based on ferrimagnetic materials, as well as related effects in antiferromagnets.