We study Kerr frequency combs and dissipative Kerr solitons in silicon photonic crystal coupled-cavity waveguides (CCWs) with globally optimized dispersion at telecom wavelengths. The corresponding threshold for comb generation is found to explicitly depend on the main CCW figures of merit, namely, the mode volume, the normal-mode quality factor, and the slow-light group index. Our analysis is carried out by solving the nonlinear dynamics of the CCW Bloch modes in the presence of Kerr nonlinearity and two-photon absorption. Our results open the way to CCW comb generation via dispersion engineering and slow-light enhancement.

Imaging of fabricated nanostructures or nanomaterials covered by dielectrics is highly sought after for diagnostics of optoelectronics components. We show imaging of atomically thin ${\mathrm{Mo}\mathrm{S}}_2$ flakes grown on ${\mathrm{Si}\mathrm{O}}_2$-covered $\mathrm{Si}$ substrates and buried beneath ${\mathrm{Hf}\mathrm{O}}_2$ overlayers up to 120 nm in thickness using photoemission electron microscopy with deep-UV photoexcitation. Comparison of photoemission yield (PEY) to modeled optical absorption evinced the formation of optical standing waves in the dielectric stacks (i.e., cavity resonances of ${\mathrm{Hf}\mathrm{O}}_2$ and ${\mathrm{Si}\mathrm{O}}_2$ layers on $\mathrm{Si}$). The presence of atomically thin ${\mathrm{Mo}\mathrm{S}}_2$ flakes modifies the optical properties of the dielectric stack locally. Accordingly, the cavity resonance condition varies between the sample locations over buried ${\mathrm{Mo}\mathrm{S}}_2$ and surrounding areas, resulting in image contrast with submicron lateral resolution. This subsurface sensitivity underscores the role of optical effects in photoemission imaging with low-energy photons. This approach can be extended to nondestructive imaging of buried interfaces and subsurface features needed for analysis of microelectronic circuits and nanomaterial integration into optoelectronic devices.

We design a solid mazelike rod to achieve sound superscattering. Because of the near degeneracy of resonances in multiple channels in the solid mazelike rod, the scattering contributions from these resonances can overlap to break the so-called single-channel limit of subwavelength structures, and thus achieve extremely strong sound scattering even in the deep-subwavelength regime. Moreover, we provide an experimental demonstration of the sound-superscattering phenomenon, which verifies the theoretical proposal. Our study provides a way to strongly strengthen sound-matter interaction, which may be useful for a great variety of practical applications in acoustic antennas, absorption, and sensing.

Measuring the orbital-angular-momentum (OAM) states of electron beams is of great importance in diverse applications. Here, we demonstrate a method to effectively measure the OAM spectrum of an electron beam by exploiting a two-dimensional Dammann vortex grating (DVG). This grating enables us to simultaneously measure an input electron beam in a transmission electron microscope using its OAM components with values between −10ħ and 10ħ (OAM spectrum). We then experimentally evaluate the performance of the DVG OAM analyzer when measuring electron beams generated by spiral zone plates and nanofabricated magnetic needles. Our evaluation supports the validity of this approach, which paves the way toward enabling a wide range of electron OAM applications, including in nanoscale imaging and in materials science.

Achieving Ohmic contact for two-dimensional- (2D) based electronics is important yet challenging. Here through first-principles calculations, we predict that a ${\mathrm{Nb}\mathrm{S}}_2$ monolayer is an excellent electrode for p-type Ohmic contacts for 2D materials. Dipole analysis indicates van der Waals interfacial interaction and high electrode work function are critical for asymmetric dipole compensation to maintain the Ohmic contact for ${\mathrm{Nb}\mathrm{S}}_2/\mathrm{BP}$ and ${\mathrm{Nb}\mathrm{S}}_2/{\mathrm{W}\mathrm{Se}}_2$. p-type Ohmic contacts for both heterostructures are independent of gating up to very large electric field (7 V/nm) suggesting good stability for device applications. Our work provides a practical strategy to realize stable p-type Ohmic contacts for future 2D nanoelectronics.

Understanding the biomechanical properties of red blood cells (RBCs) is crucial for many pathological analyses and diagnoses of human diseases. Here, we construct the so-called “tug-of-war” (TOW) optical tweezers, consisting of a pair of elongated diverging beams, to study the deformability of human RBCs. Such an optical tweezers system gives rise to object-adapted optical potentials that can stably trap, squeeze, and stretch single RBCs under different osmotic conditions without tethering or mechanical movement. Even at low trapping power, the TOW tweezers can exert a force of 18 pN, which is at least two times stronger than that of dual-trap optical tweezers based on conventional Gaussian beams, leading to more than 15% deformation of the cell shape. From a direct comparison of the trapping forces and shear modulus of the RBCs under different osmotic conditions, we find that the cell deformability follows a trend: hypotonic > isotonic > hypertonic. This work exemplifies another photonic tool with advanced beam-shaping techniques for biomechanical studies of living cells that is promising for applications such as distinguishing healthy and diseased cells and intracellular delivery.

Low- and broadband-frequency sound absorption promotes myriad practical applications and scientific endeavors. Yet emerging metamaterial concepts enable such sound absorption only by the use of a complex assembly of attenuator constituents or by the addition of heavy undesirable mass. In this study, multiple low-frequency hybrid resonances are achieved in a soft-lightweight-material-based Helmholtz resonator. By replacing the rigid walls of a traditional Helmholtz resonator with compliant walls and by tailoring the relative structural and acoustic compliances, a unique multiphysics coupling among the material, structure, and sound is realized. These coupling mechanisms yield hybrid resonances that can be used for subwavelength, broadband, and near-total absorption of sound. As a result, the compliant-material resonator exploits a lightweight-material monolithic design that exerts dramatic and tunable control over low-frequency and broadband acoustic-energy transfer. This paper details analytical and experimental investigations to test the concept and reveals strategies for near-total absorption at arbitrary subwavelength frequencies.

A coherent interface between temporal and spatial degrees of freedom (DOFs) allows one to use photons to take advantage of both types of DOF in quantum information processing. Previous interfaces either suffer from a typical loss of 1–3 dB or disturb the polarization DOF in the conversion process. Here we realize a low-loss polarization-independent coherent interface between temporal and spatial DOFs, specifically the time-bin and path modes. The experimental loss is 0.2 dB, and the fidelity of the conversion process is found by tomography to be 0.970 (0.947) without (with) considering the polarization DOF. As an application, our interface transforms a time-bin qubit output from an entanglement distribution channel to a path qubit, which allows postselection-loophole-free measurement of the Bell inequality. With its low loss and polarization independence, our interface promises applications in coherent conversion from hybrid temporal-polarization states to spatial-polarization states and could be put into a cavity to boost the generation rate of multiphoton polarization-entangled sources or enhance the scalability of sequential quantum metrology.

Silicon-based accelerometers suffer from high temperature sensitivity due to the thermoelastic effect of silicon. In order to alleviate this effect for high-precision acceleration measurement, several technologies have been reported, including both active and passive approaches. However, the existing methods either use extra circuits and devices with more complexity and power consumption or affect the mechanical and electrical characteristics of the accelerometer suspensions. In order to eliminate those side effects, this paper introduces a passive approach, which applies silicon-solder-bilayer thermal actuators at the base of the suspension to passively compensate the thermally induced displacement of the accelerometer’s proof mass, to reduce the thermoelastic response of the silicon-based accelerometers. The proposed thermal actuator based on the shrink-fit technology can provide stable bonding with silicon structures and leads to good agreement of the theoretical model with both the simulation and experimental results. The thermal actuator is applied to a micromachined vertical seismic accelerometer, which has a peak sensitivity of $0.3\times {10}^{-8}\mathrm{m}{\mathrm{s}}^{-2}(\sqrt{\mathrm{Hz}}{)}^{-1}$ for picking up seismic signals on Mars, to reduce its temperature sensitivity. Both the preliminary test of the displacement thermal response by a commercial laser displacement transducer and the thermal-cycling-experiment results with the readout electricity show that this passive method can reduce the temperature sensitivity of the silicon-based vertical seismic accelerometer by at least 2 orders of magnitude. By applying this technology and the wind and thermal shield (WTS), the overall temperature-related noise is $0.26\times {10}^{-8}\mathrm{m}{\mathrm{s}}^{-2}(\sqrt{\mathrm{Hz}}{)}^{-1}$ at 0.1 Hz, which is comparable to the intrinsic noise floor of the seismic accelerometer, meeting the mission’s requirement. The temperature-compensated seismic accelerometer package has been used as the payload of the Interior Exploration using the Seismic Investigations, Geodesy, and Heat Transport (InSight) lander, which landed successfully on Mars on November 26, 2018, with the seismic accelerometers operating since Martian day (sol) 4.

Developing a high-efficiency coherent nonlinear light source is a critical step for photonic quantum technologies in signal processing, imaging, and switching. A promising approach is second-harmonic generation (SHG) via intersub-band transitions in a semiconductor quantum-well structure with a specific plasmon resonant mode of metal structures. There are, however, two significant challenges with this approach. First, limited by the conduction-band offset, the SHG wavelength based on intersub-band transitions is unlikely to extend into the visible region. Second, the high dissipative losses of plasmonic metal nanostructures could severely limit their applicability. Here we demonstrate an alternative configuration using interband excitonic transitions in an all-dielectric multiple-quantum-well metasurface capable of achieving high SHG conversion efficiency in the visible region. Taking advantage of the magnetic resonance of the multiple-quantum-well metasurface, the tightly concentrated optical field that is induced in the metasurface is responsible for boosting the conversion efficiency to about $2\times {10}^{-7}$. This demonstration opens a viable path toward a coherent light source using SHG that is extended to the visible region and beyond with high conversion efficiency, enabling nanophotonic quantum-information applications.

The ability to shape ultrasound fields is important for particle manipulation, medical therapeutics, and imaging applications. If the amplitude and/or phase is spatially varied across the wave front, then it is possible to project “acoustic images.” When attempting to form an arbitrary desired static sound field, acoustic holograms are superior to phased arrays due to their significantly higher phase fidelity. However, they lack the dynamic flexibility of phased arrays. Here, we demonstrate how to combine the high-fidelity advantages of acoustic holograms with the dynamic control of phased arrays in the ultrasonic frequency range. Holograms are used with a 64-element phased array, driven with continuous excitation. Movement of the position of the projected hologram via phase delays that steer the output beam is demonstrated experimentally. This allows the creation of a much more tightly focused point than with the phased array alone, while still being reconfigurable. It also allows the complex movement at a water-air interface of a “phase surfer” along a phase track or the manipulation of a more arbitrarily shaped particle via amplitude traps. Furthermore, a particle manipulation device with two emitters and a single split hologram is demonstrated that allows the positioning of a “phase surfer” along a one-dimensional axis. This paper opens the door for new applications with complex manipulation of ultrasound while minimizing the complexity and cost of the apparatus.

A magnetic skyrmion usually refers to a twisted spin texture in a uniformly aligned magnetization state. Such spin texture is protected by topology, which makes the skyrmion a stable texture under small perturbations. Thus, skyrmions have attracted great interest for possible applications as an ideal information carrier. Most magnetic skyrmion studies have focused on perpendicularly magnetized systems, where the skyrmion topological charge is determined by the relative orientation between the core and outer perpendicular magnetization directions. Thus, skyrmions with opposite signs of topological charges do not seem to coexist in the same magnetic domain. Here we show that there also exists a different type of magnetic skyrmion with surrounding spins that are uniformly aligned to the in-plane direction. A clear feature of this in-plane skyrmion is that skyrmions with opposite signs of topological charges can coexist with each other. Proper choice of magnetization and Dzyaloshinskii-Moriya interaction leads to a window for the existence of this in-plane skyrmion. These findings demonstrate the inherent possibility of a double-bit transfer in a single magnetic wire, which is not possible in a perpendicularly magnetized system.

Computational reversibility is necessary for quantum computation and inspires the development of computing systems, in which information carriers are conserved as they flow through a circuit. While conservative logic provides an exciting vision for reversible computing with no energy dissipation, the large dimensions of information carriers in previous realizations detract from the system efficiency, and nanoscale conservative logic remains elusive. We therefore propose a nonvolatile reversible computing system in which the information carriers are magnetic skyrmions, topologically-stable magnetic whirls. These nanoscale quasiparticles interact with one another via the spin Hall and skyrmion Hall effects as they propagate through ferromagnetic nanowires structured to form cascaded conservative logic gates. These logic gates can be directly cascaded in large-scale systems that perform complex logic functions, with signal integrity provided by clocked synchronization structures. The feasibility of the proposed system is demonstrated through micromagnetic simulations of Boolean logic gates, a Fredkin gate, and a cascaded full adder. As skyrmions can be transported in a pipelined and nonvolatile manner at room temperature without the motion of any physical particles, this skyrmion logic system has the potential to deliver scalable high-speed low-power reversible Boolean and quantum computing.

If not oriented perfectly isotropically, the strong dipole moment of polar organic semiconductor materials such as tris-(8-hydroxyquinolate)aluminum (${\mathrm{Alq}}_3$) will lead to the buildup of a giant surface potential (GSP) and thus to a macroscopic dielectric polarization of the organic film. Despite this having been a known fact for years, the implications of such high potentials within an organic layer stack have only been studied recently. In this work, the influence of the GSP on hole injection into organic layers is investigated. Therefore, we apply a concept called dipolar doping to devices consisting of the prototypical organic materials $N$,$N^{\prime }$-Di(1-naphthyl)-$N$,$N^{\prime }$-diphenyl-(1,$1^{\prime }$-biphenyl)-4,$4^{\prime }$-diamine (NPB) as nonpolar host and ${\mathrm{Alq}}_3$ as dipolar dopant with different mixing ratios to tune the GSP. The mixtures are investigated in single-layer monopolar devices as well as bilayer metal/insulator/semiconductor structures. Characterization is done electrically using current-voltage ($I$-$V$) characteristics, impedance spectroscopy, and charge extraction by linearly increasing voltage and time of flight, as well as with ultraviolet photoelectron spectroscopy. We find a maximum in device performance for moderate to low doping concentrations of the polar species in the host. The observed behavior can be described on the basis of the Schottky effect for image-force barrier lowering, if the changes in the interface dipole, the carrier mobility, and the GSP induced by dipolar doping are taken into account.

We suggest and discuss a concept of a deterministic integrated source of nonclassical light based on the coherent diffusive photonics, a coherent light flow in a system of dissipatively coupled waveguides. We show how this practical quantum device can be realized with a system of single-mode waveguides laser inscribed in nonlinear glass. We describe a hierarchy of models, from the complete multimode model of the waveguide network to the single mode coupled to a bath, analyze the conditions for validity of the simplest single-mode model and demonstrate feasibility of the generation of bright sub-Poissonian light states merely from a coherent input. Notably, the generation of nonclassical states occurs at the initial stages of the dynamics, and can be accounted for in the linear model that allows us to circumvent the prohibiting computational complexity of the exact full quantum representation.

The reduction of nanoelectronic devices to sub-10 nm sizes raises the prospect of electronics at the atomic scale, while also facilitating studies on nanoscale device physics. Single-atom transistors, where the current-switching element is formed by one atom and the information packet size is reduced to one electron, can create electronic switches scaled to their ultimate physical limits. Hitherto, single-atom transistor operation has been limited to low temperatures due to shallow quantum wells, which inhibit room-temperature nanoelectronic applications. Furthermore, the interaction between multiple single-atom elements at room temperature has yet to be demonstrated. Here, we show that quantum interactions between $\mathrm{P}$ dopants in $\mathrm{Si}/{\mathrm{Si}\mathrm{O}}_2/\mathrm{Si}$ single-atom transistors lead to room-temperature double quantum dot behavior. Hexagonal regions of charge stability and gate-controlled tunnel coupling between $\mathrm{P}$ atoms are observed at room temperature. Image processing is used to help reduce observer bias in data analysis. Single-electron device simulation is used to investigate evolution of the charge-stability region with varying capacitance and resistance. In combination with extracted tunnel capacitances and resistances, this allows experimental trends to be reproduced and provides information on the dopant-atom arrangement.

We present measurements of the capacitive coupling energy and the interdot capacitances in a linear quadruple-quantum-dot array in undoped $\mathrm{Si}$/$\mathrm{Si}\mathrm{Ge}$. With the device tuned to a regime of strong ($>1\mathrm{GHz}$) intra-double-dot tunnel coupling, as is typical for double-dot qubits, we measure a capacitive coupling energy of $20.9\pm 0.3\mathrm{GHz}$. In this regime, we demonstrate a fitting procedure to extract all the parameters in the four-dimensional Hamiltonian for two capacitively coupled charge qubits from a two-dimensional slice through the quadruple-dot charge-stability diagram. We also investigate the tunability of the capacitive coupling energy, using interdot barrier gate voltages to tune the inter- and intra-double-dot capacitances, and change the capacitive coupling energy of the double dots over a range of 15–32 GHz. We provide a model for the capacitive coupling energy based on the electrostatics of a network of charge nodes joined by capacitors, which shows how the coupling energy should depend on inter-double-dot and intra-double-dot capacitances in the network, and find that the expected trends agree well with the measurements of coupling energy.

Interleaving fins can significantly increase heat transfer by increasing the effective area per unit base area. The fins are separated uniformly by a gap, which is filled with a flow medium to control the heat flux. The heat flux between the plates depends strongly on the thermal conductivity of the fin material and the medium between them, as well as the dimensions. In earlier studies, an empirical fitting method has been used to determine the total effectiveness of the fins. However, it required complete characterization of the fins for each new set of operating conditions. In this paper, a simplified analytical model is developed, which still preserves the main physical traits of the problem. This model reveals the dimensionless parameter group containing both the material properties and the fin geometry that govern the heat transfer. Rigorous testing of the model using a numerical finite-element model shows an accuracy within 2% over a large parameter space, varying both dimensions and material properties. Lastly, this model is put to the test with previously measured experimental data and good agreement is obtained.

Hybrid quantum registers consisting of different types of qubit offer a range of advantages as well as challenges. The main challenge is that some types of qubit react only slowly to external control fields, thus considerably slowing down the information-processing operations. One promising approach that has been tested in a number of cases is to use indirect control, where external fields are applied only to qubits that interact strongly with resonant excitation pulses. Here, we use this approach to indirectly control the nuclear spins of a nitrogen-vacancy center, using microwave pulses to drive the electron spin, combined with free precession periods optimized for generating logical gate operations on the nuclear spins. The scheme provides universal control and we present two typical applications: polarizing the nuclear spin and measuring nuclear-spin free-induction-decay signals, both without applying radio-frequency pulses. This scheme is versatile, as it can be implemented over a wide range of magnetic field strengths and at any temperature.