We study simultaneous parametric oscillations in a system composed of two distributed-element-circuit Josephson parametric oscillators in the single-photon Kerr regime coupled via a static capacitance. The energy of the system is described by a two-bit Ising Hamiltonian with an effective coupling whose amplitude and sign depend on the relative phase between parametric pumps. We demonstrate that the binary phases of the parametric oscillations are correlated with each other, and that the parity and strength of the correlation can be controlled by adjusting the pump phase. The observed correlation is reproduced in our simulation taking pure dephasing into account. The present result demonstrates the tunability of the Hamiltonian parameters by the phase of external microwave, which can be used in the Ising machine hardware composed of the Kerr parametric oscillator network.

We theoretically report a remarkable revolving effect of electron flow when applying a lattice temperature gradient across an asymmetric double-barrier heterostructure. Depending on whether the lattice temperature increases or decreases, we demonstrate that electrons respectively absorb or emit a phonon and subsequently go back to the reservoir from which they have been injected. Our simulation code, which self-consistently solves the nonequilibrium Green’s function framework and the heat equation, is capable of calculating the electron temperature and electrochemical potential inside the device. By investigating those nonequilibrium thermodynamic quantities, we show that the revolving effect is due to the sign inversion of the local electron distribution. In particular, simulation results evidenced a variation of the electrochemical potential inside the device to compensate the temperature gradient, and to maintain the electrostatic neutrality in the access regions. Finally, we propose an analytic model which provides an intuitive picture of the effect, and discuss the possibility to use such behavior in the new context of heat management in nanostructures.

We designed and experimentally demonstrated a four-terminal superconducting device, a “quadristor,” that can function as a nonlatching (reversible) superconducting switch from the diode regime to the resistive state by application of a control current much smaller than the main transport current. The device uses a vortex-based superconducting-diode mechanism that is switched back and forth via the injection of flux quanta through auxiliary current leads. Our finding opens a new research area in the field of superconducting electronics.

Recent advances in quantum computing and their increased availability has led to a growing interest in possible applications. Among those is the solution of partial differential equations (PDEs) for, e.g., material or flow simulation. Currently, the most promising route to useful deployment of quantum processors in the short to near term are so-called hybrid variational quantum algorithms (VQAs). Thus, variational methods for PDEs have been proposed as a candidate for quantum advantage in the noisy intermediate-scale quantum (NISQ) era. In this work, we conduct an extensive study of utilizing VQAs on real quantum devices to solve the simplest prototype of a PDE—the Poisson equation. Although results on noiseless simulators for small problem sizes may seem deceivingly promising, the performance on quantum computers is very poor. We argue that direct resolution of PDEs via an amplitude encoding of the solution is not a good use case within reach of today’s quantum devices—especially when considering large system sizes and more complicated nonlinear PDEs that are required in order to be competitive with classical high-end solvers.

Thermoelectric (TE) coolers show considerable promise for replacing aging refrigeration devices, which suffer from the poor low-temperature performance of most TE materials due to the small entropy of carriers and weak lattice vibrational anharmonicity. Here we propose that two-dimensional (2D) semiconductors with multiple bonding layers can be potential TE cooling materials, and the 2D A$\mathrm{Mn}$X (A = $\mathrm{Sr},\mathrm{Ba}$; X = $\mathrm{Sn},\mathrm{Pb}$) family is identified as an example. Owing to the d-orbital inversion of the $\mathrm{Mn}$ element, both the valence and conduction bands possess continuously square-shaped band edges with slight energy divergence, which trigger high mobility and sharply enhanced density of states near the Fermi level, thereby producing large power factors for both p- and n- type materials. Moreover, the coexistence of soft covalent bonds and ionic layers lowers phonon group velocity and strengthens phonon scattering, resulting in extremely low lattice thermal conductivity. At optimal carrier concentrations, both p- and n-type $\mathrm{SrMnPb}$ quintuple layers can reach ultrahigh room-temperature ZT above 2.0, with excellent average ZT beyond 1.8 from 150 to 350 K. This work not only proposes a tellurium-free alternative for TE refrigeration, but also provides general indicators for guiding the search for high-performance TE cooling materials.

Quantum reservoir computing (QRC) exploits the information-processing capabilities of quantum systems to solve nontrivial temporal tasks, improving over their classical counterparts. Recent progress has shown the potential of QRC exploiting the enlarged Hilbert space, but real-time processing and the achievement of a quantum advantage with efficient use of resources are prominent challenges towards viable experimental realizations. In this work, we propose a photonic platform suitable for real-time QRC based on a physical ensemble of reservoirs in the form of identical optical pulses recirculating through a closed loop. While ideal operation achieves maximum capacities, statistical noise is shown to undermine any quantum improvement. We propose a strategy to overcome this limitation and sustain the QRC performance when the size of the system is scaled up. The protocol is conceived for experimental implementations to be viable with current technology.

To overcome the memory wall based on the von Neumann architecture, in-memory computing has been intensively studied as a potential solution. Recently, an alternative type of spintronic material, namely, bipolar magnetic semiconductors (BMSs), has attracted much attention because of its opposite spin-polarized valence and conduction bands, which have thus facilitated electrically tunable spin transport. Here, we propose a logic-in-memory device with a traditional field-effect-transistor (FET) configuration by making use of the ferromagnetic and semiconducting features of BMSs simultaneously. Two representative BMSs (2H-${\mathrm{VS}}_2$ and semihydrogenated graphene) are selected as the FET channels, and the transport properties of these devices are investigated by using ab initio quantum transport simulations. The spin polarization of the current reaches up to 98%, enabling the device to provide an ideal spin-polarization signal. The distinct electronic structures under the two magnetic states and the electrically tunable spin polarization allow the devices to perform logic operations directly in situ. Two-input logic, including xor and nonvolatile and or nor, can be realized with one and two BMS FETs, respectively, efficiently decreasing the integration density of logic circuits. This work provides an alternative route to realize fused storage and computing functions in a transistor.

The growing demand for ultrafast information transmission in integrated sensing and communications has fueled extensive research on spoof surface-plasmon polaritons (SSPPs). However, existing studies have been limited by structural design constraints, resulting in single-frequency phase modulation and hindered high-order modulation capabilities. Here, we propose a superthin programmable modulator utilizing SSPP waveguides and validate its performance through experimental verification. Our modulator enables phase control across a wider bandwidth by real-time manipulation of SSPP waveguides in a programmable manner, facilitating quadrature-phase-shift-keying modulation. Moreover, this modulator opens up possibilities for achieving higher-order modulation. Measurement results demonstrate the effectiveness of programmable plasma metamaterials in modulating surface electromagnetic waves, with significant implications for integrated sensing and communications applications.

Transparent light-converting ${\mathrm{Y}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}:\mathrm{Ce}$ (YAG:$\mathrm{Ce}$) ceramics have become promising materials for advanced light-emitting diode and laser-driven white-light-generation technology. However, their functionality is highly dependent on factors such as structural quality, uniformity of dopant distribution, the presence of defects, and the cost of fabrication. The emission of YAG:$\mathrm{Ce}$ ceramics remains thermally stable when high-power-density laser excitation is uniformly spread over the entire surface area of the ceramics due to light-scattering processes. The creation of light-scattering centers that can provide homogeneous white light in ceramics is crucial. One of the drawbacks of YAG:$\mathrm{Ce}$ as a material for converting ultraviolet emission into white light is the lack of a red component, which results in cold light and a low color rendering index. Therefore, the codoping of YAG:${\mathrm{Ce}}^{3+}$ with red-emitting ions (${\mathrm{Er}}^{3+}$, ${\mathrm{Ho}}^{3+}$, ${\mathrm{Nd}}^{3+}$, ${\mathrm{Pr}}^{3+}$, and ${\mathrm{Cr}}^{3+}$) was carried out and slight nonstoichiometry was induced in the present study to improve the photoconversion parameters. The phase purity of the studied ceramics was analyzed using powder x-ray diffraction and SEM combined with energy-dispersive spectroscopy (EDS). EDS studies revealed that nonstoichiometric ceramics contained ${\mathrm{Al}}_2{\mathrm{O}}_3$ phase inclusions that acted as light-scattering centers. Optical transmittance and absorption spectra measurements revealed the presence of light-scattering centers imposed by ${\mathrm{Al}}_2{\mathrm{O}}_3$ phase inclusions and nanodefects related to perturbations of the local lattice structure by dopants. EDS mapping and photoluminescence analysis showed the formation of $\mathrm{Ce}$-$\mathrm{Ln}$,$\mathrm{Cr}$ ($\mathrm{Cr}$ is a transition metal) pairs and the availability of energy transfer between the pair-forming ions. Intrinsic thermal quenching of ${\mathrm{Ce}}^{3+}$ luminescence started above 400 K. The nonstoichiometric YAG:$\mathrm{Ce},\mathrm{Nd}$ sample showed luminescence stability up to 650 K with a luminous efficacy of 198 lm/W. The photoconversion parameters of the transparent ceramic packaged with a blue light-emitting diode or a laser diode were compared. It was shown that the color temperature of ceramic emissions could be controlled by the spectral width of the excitation beam. Thermally stimulated luminescence was applied to investigate the deep trapping centers imposed by the codopants. A detailed EPR study revealed the presence of ${\mathrm{F}}^{+}$, ${\mathrm{O}}^{-}$, and ${\mathrm{Ce}}^{4+}$ centers.

Optimizing the cooperativity between two distinct particles is an important feature of quantum information processing. Of particular interest is the coupling between spin and phonon, which allows for integrated long-range communication between gates operating at gigahertz frequency. Using local light scattering, we show that, in magnetic planar geometries, this attribute can be tuned by adjusting the orientation and strength of an external magnetic field. The coupling strength is enhanced by about a factor of 2 for the out-of-plane magnetized geometry where the Kittel mode is coupled to circularly polarized phonons, compared to the in-plane one where it couples to linearly polarized phonons. We also show that the overlap between magnon and phonon is maximized by matching the Kittel frequency with an acoustic resonance that satisfies the half-wave-plate condition across the magnetic film thickness. Taking the frequency dependence of the damping into account, a maximum cooperativity of about 6 is reached in garnets for the normal configuration near 5.5 GHz.

In addition to the need for stable and precisely controllable qubits, quantum computers take advantage of good readout schemes. Superconducting qubit states can be inferred from the readout signal transmitted through a dispersively coupled resonator. This work proposes a readout classification method for superconducting qubits based on a neural network pretrained with an autoencoder approach. A neural network is pretrained with qubit readout signals as autoencoders in order to extract relevant features from the data set. Afterward, the pretrained-network inner-layer values are used to perform a classification of the inputs in a supervised manner. We demonstrate that this method can enhance classification performance, particularly for short- and long-time measurements where more traditional methods present inferior performance.

In conventional inductive wireless power devices, the energy is transferred via only reactive near fields, which is equivalent to nonradiative Förster energy transfer in optics. Radiation from transmitting and receiving coils is usually considered as a parasitic effect that reduces the power-transfer efficiency. As long as the distance between the two antennas is small compared to the antenna size, conventional wireless power-transfer devices offer rather high power-transfer efficiency, of the order of 80%–90%. However, for larger distances, the transfer efficiency dramatically drops, making such devices impractical. In this paper, we develop a dynamic theory of wireless power transfer between two small loop antennas, clarify the role of far-field radiation, and find a possibility to realize efficient wireless power transfer at large distances utilizing the regime of radiation suppression due to optimized mutual dynamic interactions between the transmitting and receiving antennas. The analytical results are validated by simulations and measurements, and they open a possibility to greatly expand the range of distances of compact wireless power-transfer devices. The developed theory can also be applied to coupling between antennas of different types and to energy transfer between nano-objects.

In this paper, we develop an exact analytical quantum theory for field emission from surfaces with a nearby quantum well, by solving the one-dimensional time-independent Schrödinger equation. The quantum well, which may be introduced by ions, atoms, nanoparticles, etc., is simplified as a square potential well with depth H, width d, and distance to the surface L. The theory is used to analyze the effects of the quantum well (d, H, and L), the cathode properties (work function W and Fermi energy $E_F$), and dc field F. It is found that the quantum well can lead to resonant tunneling enhanced field emission up to several orders of magnitude larger than that from bare cathode surfaces. In the meantime, the electron-emission-energy spectrum is significantly narrowed. The strong enhancement region is bounded by the conditions eFL + H ≥ W + C and eFL ≤ W, with e being the elementary charge (positive) and C a constant dependent on dc field F. It is also found that the linear shift of resonance peaks in the electron-emission-energy spectrum with dc field F follows ${\epsilon }_p={\epsilon }_{p0}-eFL$, with ${\epsilon }_{p0}$ being approximately the eigenenergies for electrons confined in a square potential well without a dc field. The theory provides insights for the design of high-efficiency field emitters, which can produce a high current and highly collimated electron beams.

Willis dynamic homogenization theory revealed that the effective linear momentum of elastic composites is coupled to their effective strain. Recent generalization of Willis dynamic homogenization theory to the case of piezoelectric composites further revealed that their effective linear momentum is also coupled to the effective electric field. Here, we introduce the simplest possible model—a one-dimensional discrete model—that exhibits this so-called electromomentum coupling in subwavelength composites. We utilize our model to elucidate the physical origins of this phenomenon, illustrate its mechanism, and identify local resonances which lead to elevated Willis and electromomentum coupling in narrow frequency bands. The results provide intuitive guidelines for the design of this coupling in piezoelectric metamaterials.

Temporal modulation unlocks possibilities to dynamically control and modify the response of electromagnetic systems. Employing explicit dependencies of circuit or surface parameters on time enables the engineering of systems with conventionally unachievable functionalities. Here, we propose an alternative approach that enables the emulation of electromagnetic systems that can have arbitrary frequency dispersion and nonlinear properties, including the non-Foster response. In particular, we show that a proper modulation of a time-varying capacitor allows one to mimic a static inductance, capacitance, or resistance having arbitrary values, both positive and negative. We discuss necessary modifications of determined ideal modulation functions that ensure the stability of the system. To demonstrate the applicability of the proposed method, we introduce and simulate an invisible sensor, i.e., a device that does not produce any scattering and is capable of sensing. Three different geometries are proposed and validated using full-wave simulations. In addition to that, we discuss the stability of the systems that are modulated externally. We believe that this study introduces an alternative paradigm of using time modulations to engineer system responses that can be applied not only to electromagnetic systems (in electronics, microwaves, and optics) but also in other branches of physics.

Unpaired electronic spins at diamond surfaces are ubiquitous and can lead to excess magnetic noise. They have been observed in several studies to date, but their exact chemical nature is still unknown. We propose a simple model to explain the existence and chemical stability of surface spins associated with the ${sp}^3$ dangling bond on the (100) diamond surface using density-functional theory. We find that the (111) facet, which is naturally generated at a step edge of (100) crystalline diamond surface, can sterically protect a spinful defect. Our study reveals a mechanism for annihilation of these surface spins upon annealing, consistent with recent experimental results. We also demonstrate that the Fermi-contact term in the hyperfine coupling is not negligible between the surface spins and the surrounding nuclear spins, and thus ab initio simulation can be used to devise a sensing protocol where the surface spins act as reporter spins to sense nuclear spins on the surface.