Negatively charged nitrogen-vacancy ($\mathrm{N}\text{−}$$V^{-}$) centers in diamonds have rapidly developed due to their exceptional quantum optical and spin properties at room temperature. However, their applicability is limited by broad phonon-sideband emission with feeble coherent emission at the zero-phonon line (ZPL). This calls for the exploration of photonic cavities to enhance ZPL emission. We propose an easy-to-fabricate hybrid metal-dielectric nanocavity with low mode volume to enhance ZPL emission while suppressing phononic emission channels due to different $\mathrm{N}\text{−}$V charge states. We find a 400% enhancement in the emission rate and outcoupling of emitted light at the ZPL with better directivity by deterministic positioning of the $\mathrm{N}\text{−}$$V^{-}$ inside the nanocavity, corroborated by numerical simulations. The pump-dependent measurements confirm better emission saturation intensity for the cavity-coupled $\mathrm{N}\text{−}$$V^{-}$s. The proposed tunable nanocavity structure can be applied to a broad range of quantum emitters to control their emission so that their use in quantum technologies could be improved.

We study a job-shop scheduling problem for an automatized robot in a high-throughput laboratory and a traveling-salesperson problem with recently proposed digitized counterdiabatic quantum optimization (DCQO) algorithms. In DCQO, we find the solution of an optimization problem via an adiabatic quantum dynamics, which is accelerated with counterdiabatic protocols. Thereafter, we digitize the global unitary to encode it in a digital quantum computer. For the job-shop scheduling problem, we aim at finding the optimal schedule for a robot executing a number of tasks under specific constraints, such that the total execution time of the process is minimized. For the traveling-salesperson problem, the goal is to find the path that covers all cities and is associated with the shortest traveling distance. We consider both hybrid and pure versions of DCQO algorithms and benchmark the performance against digitized quantum annealing and the quantum approximate optimization algorithm (QAOA). In comparison to QAOA, the DCQO solution is improved by several orders of magnitude in success probability using the same number of two-qubit gates. Moreover, we implement our algorithms on cloud-based superconducting and trapped-ion quantum processors. Our results demonstrate that circuit compression using counterdiabatic protocols is amenable to current noisy intermediate-scale quantum hardware and can solve logistics scheduling problems, where other digital quantum algorithms show insufficient performance.

Two-dimensional Ruddlesden-Popper perovskites have garnered significant attention due to their excellent environmental stability, tunable photophysical properties, and other advantageous characteristics. Although two-dimensional perovskites have been extensively studied in the field of photoluminescence, their application in photovoltaics has been limited due to high exciton-binding energy. Recently, another Ruddlesden-Popper perovskite ${\mathrm{Cs}}_2{\mathrm{Pb}(\mathrm{SCN})}_2{\mathrm{Br}}_2$ has been synthesized. Compared to most two-dimensional perovskites, ${\mathrm{Cs}}_2{\mathrm{Pb}(\mathrm{SCN})}_2{\mathrm{Br}}_2$ boasts the advantages of low exciton-binding energy and a narrow optical band gap. To explore the potential of two-dimensional perovskites in photovoltaic applications, an all-inorganic two-dimensional heterojunction $\mathrm{C}{\mathrm{s}}_2\mathrm{Pb}(\mathrm{SCN}{)}_2\mathrm{B}{\mathrm{r}}_2/\mathrm{Mo}{\mathrm{S}}_2$ was investigated using first-principles calculations based on density-functional theory (DFT). Our calculation results demonstrate that the heterojunction exhibits significantly enhanced optical absorption properties and carrier mobility compared to ${\mathrm{Cs}}_2{\mathrm{Pb}(\mathrm{SCN})}_2{\mathrm{Br}}_2$ material. The heterojunction features a typical type-II band alignment, making it highly suitable for photovoltaic applications such as solar cells. We also applied a longitudinal electric field to the heterojunction in calculations, thereby regulating its band alignment. The calculation results reveal that the type-II band alignment of the heterojunction can be transformed into type-I and type-III alignments. These findings significantly expand the application potential of the heterojunction in electronic and optoelectronic devices.

Recently, low-dimensional metal halides have attracted considerable attention for their highly versatile tunability and outstanding broadband luminescence characteristics. Concurrently, there is an increasing number of studies focusing on the modulation of photoluminescence properties via doping, particularly with ${\mathrm{GSP}}^{2+}$ (${\mathrm{Ge}}^{2+}$, ${\mathrm{Sn}}^{2+}$, and ${\mathrm{Pb}}^{2+}$) ions possessing ${\mathrm{ns}}^2$ lone-pair electrons (originating from neutral atoms with an ${ns}^2{np}^2$ electronic configuration), which are considered ideal dopants. However, numerous promising experimental outcomes resulting from doping depend significantly on empirical knowledge and fortuitous circumstances. Comprehensive theoretical research is crucial to effectively guide experimental approaches and minimize resource wastage. In this study, we employ ${\mathrm{GSP}}^{2+}$ ions doped into ${\mathrm{Cs}}_2{\mathrm{Zn}\mathrm{Br}}_4$ as a model to explore the regulatory mechanisms and principles that govern the effects of various ${\mathrm{GSP}}^{2+}$ ions on zero-dimensional metal halides. Our findings indicate that ${\mathrm{GSP}}^{2+}$ ions doped into ${\mathrm{Cs}}_2{\mathrm{Zn}\mathrm{Br}}_4$ form $[{\mathrm{MBr}}_4{]}^{2-}$ (M = $\mathrm{Ge}$, $\mathrm{Sn}$, and $\mathrm{Pb}$) tetrahedra, which undergo deformation in the excited state, leading to self-trapping emissions in initially weak-luminescent ${\mathrm{Cs}}_2{\mathrm{Zn}\mathrm{Br}}_4$. Additionally, there is a gradual decrease in the transition dipole moment and a continuous increase in emission energy from ${\mathrm{Cs}}_2{\mathrm{Zn}\mathrm{Br}}_4:\mathrm{Ge}$ to ${\mathrm{Cs}}_2{\mathrm{Zn}\mathrm{Br}}_4:\mathrm{Sn}$ to ${\mathrm{Cs}}_2{\mathrm{Zn}\mathrm{Br}}_4:\mathrm{Pb}$. Furthermore, the luminescence lifetime of ${\mathrm{Cs}}_2{\mathrm{Zn}\mathrm{Br}}_4:\mathrm{Pb}$ is shorter than that of ${\mathrm{Cs}}_2{\mathrm{Zn}\mathrm{Br}}_4:\mathrm{Ge}$ and ${\mathrm{Cs}}_2{\mathrm{Zn}\mathrm{Br}}_4:\mathrm{Sn}$, owing to the lower barrier for the singlet to triplet transition in ${\mathrm{Cs}}_2{\mathrm{Zn}\mathrm{Br}}_4:\mathrm{Pb}$. Our theoretical analysis will facilitate the development of more efficacious doping strategies in experimental settings.

We explore the optical properties of plasmon localization and local field enhancement in metal-plastic metasurface. The flexible metal-dielectric metasurfaces are made from modulated polycarbonate substrate coated by a thin silver film. Localization of an optical excitation is experimentally observed by near-field scanning optical microscopy within subwavelength areas in the regular open-resonator metasurface. The localized modes are seen as giant fluctuations of the local electric field spatially concentrated in hotspots, where the local field is much larger than the amplitude of the incident light. Local near-field spatial spectra consist of regularly distributed strong peaks. The maxima of the electric field are highly dependent on the sample structure. The form of the regularly distributed strong resonance peaks follows the topography obtained by atomic force microscopy. It is shown that strong electromagnetic field is concentrated in recesses where the silver film is typically thinner than on the bumps. This experimental observation is consistent with the results of computer simulations of a double-periodic metal-dielectric metasurface and the predictions of our analytical theory. It is found the silver nanofilm has strong adhesion to polycarbonate substrate.

One of the most appealing features of magnonics is the easy tunability of spin-wave propagation via external magnetic fields. Typically, this requires bulky and power-hungry electromagnets, which are not compatible with device miniaturization. Here, we propose a different approach, exploiting the stray field from permanent micromagnets integrated on the same chip of a magnonic waveguide. In our monolithic device, we employ two $\mathrm{Sm}\mathrm{Co}$ square micromagnets (10 × 10 $\text{μ}{\mathrm{m}}^2$) flanking a $\mathrm{Co}\mathrm{Fe}\mathrm{B}$ conduit at different distances from its axis, which produces a tunable transverse bias field between 7.5 and 3.0 mT in the conduit region between the magnets. This field is large enough to significantly affect the spin-wave propagation, when an external transverse bias field of 60 mT is applied to stabilize the Damon-Eshbach configuration. Spin waves excited by an antenna just outside the region between the magnets, indeed, enter a region with a variable higher (or lower) effective field depending on the parallel (or antiparallel) alignment between the external and micromagnets fields. Consequently, the attenuation length and phase shift of Damon-Eshbach spin waves can be tuned in a wide range by changing the parallel-antiparallel configuration of the external bias and the distance between $\mathrm{Sm}\mathrm{Co}$ micromagnets and the $\mathrm{Co}\mathrm{Fe}\mathrm{B}$ conduit. This work demonstrates the potential of permanent micromagnets for the realization of low-power, integrated magnonic devices with tunable functionalities.

The unique phenomena arising from Dirac cones in phononic crystals offer promising avenues for on-demand sound manipulations with compelling applications in low-power acoustic sensing and imaging. However, the practical utilization of Dirac cone–enabled phononic crystals in engineering systems is limited by a lack of significant Dirac cone tunability. In this research, we investigate an easy-to-implement method to control Dirac cones via continuous phononic lattice symmetry manipulation. For the first time, we systematically investigate and uncover how the changes in the lattice symmetry, perturbations from its perfectly symmetric configurations, alter the phononic crystal band structure, and we utilize this insight to introduce a tunable phononic crystal with Dirac cones continuously modulated to significantly change their position in the band diagram. We demonstrate experimentally how this tunability feature is leveraged to design beamformers able to generate highly directive sound beams and steer them over a wide range of angles. The single-transducer and single-degree-of-freedom actuation make the device remarkably low power and easy to realize, making it ideal for the development of practical acoustic imaging and sensing systems. Moreover, this work opens up exciting paths forward and prospects for the design and utilization of phononic crystals beyond the confines of traditional perfectly symmetric configurations.

Perfectly diffuse wave fields are the underlying assumption for noise-correlation tomography in seismology, nondestructive testing, and elastography; however, perfectly diffuse fields are rarely encountered in real-world applications. We show that homogeneously distributed magnetic microparticles allow instantaneous generation of a diffuse wave field, which can be imaged using a clinical probe connected to a fully programmable ultrasound scanner. The particles are placed inside a bilayered hydrogel and act as elastic-wave sources on excitation by a magnetic pulse. Using ultrafast ultrasound imaging coupled to phase tracking, the diffuse elastic wave field is imaged. This allows the local wave velocity to be measured everywhere on the image using noise-correlation algorithms inspired by seismology. Thanks to this instantaneous diffuse wave field, a very short acquisition time is sufficient to retrieve the wave speed contrast of a bilayered phantom. The correlation time window can be shrunk down to three time samples, which we show in a numerical simulation mimicking the experimental conditions. Our experimental and numerical results are consistent with theoretical predictions made by information theory, and they pave the way for real-time elasticity imaging. This is of particular interest for monitoring of medical treatments through real-time tissue-elasticity assessment, and it is also applicable in related fields such as seismology and nondestructive testing.

We conduct a comprehensive assessment of the electronic and optical properties, as well as photovoltaic (PV) performance parameters, for low-cost, nontoxic ${\mathrm{Mg}}_2\mathrm{Si}$ and ${\mathrm{Ca}}_2\mathrm{Si}$ using methods based on density-functional theory and the Bethe-Salpeter equation (BSE). The band gap for ${\mathrm{Mg}}_2\mathrm{Si}$ (${\mathrm{Ca}}_2\mathrm{Si}$) is found to be in the range of 0.25–0.6 (0.57–0.96) eV when the Perdew-Burke-Ernzerhof (PBE), PBE for solids (PBEsol), and modified Becke-Johnson (mBJ) functionals are used. The effective masses at the last-filled valence and first-empty conduction bands are in the range of 0.14–0.17 (1.17–1.25) $m_e$ and 0.27–0.29 (0.3–0.41) $m_e$, respectively. In the independent-particle approximation (IPA), the real and imaginary parts of the dielectric function show maximum values of $\sim 50$ (16.3) at $\sim 2.6$ (1.0) eV and $\sim 61$ (16.2) at $\sim 3.24$ (3.4) eV, respectively. Within the BSE, these respective values change to $\sim 59$ (17) at $\sim 2.5$ (0.86) eV and $\sim 65$ (16.6) at $\sim 2.68$ (3.1) eV. The excitonic effect is found to be crucial in understanding the experimental optical spectra of ${\mathrm{Mg}}_2\mathrm{Si}$. However, this effect is relatively weaker in ${\mathrm{Ca}}_2\mathrm{Si}$. In the active region of the solar spectrum, the highest absorption coefficient and lowest reflectivity change from $\sim 1.5(0.75)\times {10}^6{\mathrm{cm}}^{-1}$ and $\sim 0.39$ (0.3), respectively, in the IPA, to $\sim 1.6(0.88)\times {10}^6{\mathrm{cm}}^{-1}$ and $\sim 0.41$ (0.27) in the BSE. The present study highlights the importance of different levels of theoretical approximations for obtaining optical spectroscopy data of silicides with a high level of accuracy. Finally, we have evaluated the PV efficiency by using a spectroscopic limited maximum efficiency (SLME) calculation. On top of radiative recombination, we have also incorporated nonradiative carrier recombination at a defect trap state via the Shockley-Read-Hall (SRH) mechanism to evaluate the efficiency. Among the studied defects, interstitial $\mathrm{Mg}$ ($\mathrm{Si}$) is identified as the most stable in ${\mathrm{Mg}}_2\mathrm{Si}$ (${\mathrm{Ca}}_2\mathrm{Si}$), and this provides an SRH lifetime of $\sim 2\text{μ}\mathrm{s}$ (11.3 ms). The estimated maximum SLME using the BSE absorption spectrum is $\sim 1.3$% (31.2%), which decreases to $\sim 1.2$% (28.5%) due to SRH recombination. The present study suggests that ${\mathrm{Ca}}_2\mathrm{Si}$ (${\mathrm{Mg}}_2\mathrm{Si}$) is a potential candidate for single-junction (bottom cell in multijunction) thin-film PV devices.

We present a multiprobe transport analysis that effectively separates bulk and edge currents in large Hall bar devices with standard geometries. Applied to transport measurements on all possible four-probe configurations of six-probe Hall-bar devices made of inverted three-layer $\mathrm{In}\mathrm{As}$/$(\mathrm{Ga},\mathrm{In})\mathrm{Sb}$ quantum wells (QWs), our analysis not only reveals the presence of dissipative edge currents in the topological gap, but also allows the temperature dependence of bulk and edge conductivity to be evaluated separately. The temperature dependence of the edge conductivity for Hall-bar channels from $10$ to $70\text{μ}\mathrm{m}$ in the range of 1.5 to 45 K is consistent with the theoretical expectation of weakly interacting helical edge electrons with backscattering due to localized magnetic moments of charge impurities. We argue that these charge impurities are naturally associated with intrinsic $\mathrm{Ga}$-antisite defects, which act as double acceptors in $\mathrm{In}\mathrm{As}$/($\mathrm{Ga}$,$\mathrm{In}$)$\mathrm{Sb}$-based QWs.

Computational studies on contacts between transition-metal dichalcogenides (TMDs) and metals generally focus on understanding the interface between metal and TMD using ab initio approaches such as density functional theory. However, the computational expense inherent in ab initio simulations limits their usage in simulating more realistic contacts with larger dimensions that include doping, dielectrics, back-gate and phenomena such as image-force barrier lowering (IFBL). In this work, we perform transport simulations to calculate contact resistance in top-contacted metal-${\mathrm{MoS}}_2$ systems. We investigate the influence of spatially nonuniform doping in ${\mathrm{MoS}}_2$, metal workfunction, back-gate bias and the surrounding dielectric environment on contact resistance in metal-${\mathrm{MoS}}_2$ contacts. We find that doping in the channel region plays a more critical role compared with doping in the overlap region. We also find that a low-$\kappa$ top dielectric greatly aids in reducing the tunneling barrier and therefore the contact resistance. Furthermore, we find that an addition of merely a few nanometers of low-$\kappa$ at the right edge of the overlap region is sufficient to significantly improve contact resistance. Finally, we highlight the importance of IFBL in transport simulations by comparing contact resistance with and without IFBL. Our results show that a low-$\kappa$ top dielectric, together with doping concentration greater than ${10}^{13}{\mathrm{cm}}^{-2}$ in ${\mathrm{MoS}}_2$ and metal workfunction less than $4.4\mathrm{eV}$ are simultaneously required to realize contact resistance of less than 1 $\mathrm{k}\mathrm{\Omega }\text{μ}\mathrm{m}$ in metal-${\mathrm{MoS}}_2$ top contacts.

Two-photon frequency stabilization is a critical step for experiments related to the Rydberg-state electromagnetically induced transparency (EIT) effect, as it exploits both the high optical nonlinearity of the EIT effect and the strong electric dipole-dipole interaction among Rydberg-state atoms. Fluctuations in the two-photon frequency cause decoherence in the Rydberg-EIT system, degrading its optical nonlinearity. Here, we propose and experimentally demonstrate a counterintuitive method to enhance the stability of the two-photon frequency of probe and coupling using atomic transitions. This method leverages increased probe power or intensity beyond the power broadening threshold. This improvement in the two-photon frequency stability consequently reduces the decoherence rate of Rydberg-EIT in laser-cooled atoms. By employing the double-resonance scheme with a moderate 480-nm coupling power of 64 mW or a Rabi frequency of $2\pi \times 4.1$ MHz, the resulting fluctuation of the two-photon frequency lock was 170 kHz at an optimum 780 nm probe Rabi frequency of $2\pi \times 15.6$ MHz. Concurrently, the observed frequency fluctuation-induced decoherence rate was $2\pi \times 12$ kHz at a moderate coupling Rabi frequency of $2\pi \times 4.8$ MHz for the Rydberg-EIT transition with cold atoms. This work represents a pivotal advancement, as it furnishes sufficient stability in the two-photon frequency to meet the demands of most Rydberg-EIT applications.

Magnetic-field coils are devices utilized to generate high-precision magnetic fields across various physical research and application domains. They typically require specific profile characteristics to effectively fulfill their intended purposes. Among these characteristics, a stream-function-based method has emerged as a crucial approach for designing magnetic-field coils in complex scenarios by constructing the inverse solution according to desired magnetic-field profiles. Its feasibility and accuracy are limited by deviations from the original problem contingent upon the singularities and condition numbers of the coefficient matrix. Moreover, the limited applicability complicates the acquisition of a consistent magnetic field. To construct a fundamentally general approach, this study introduces a superadaptive stream-function design method based on active random selection. The novel method integrates the inverse solution with the Kaczmarz iterative process and incorporates nonuniform grabbing based on matrix row information. These enhancements enable a direct approximation of complex problems and circumvent the challenges encountered with a coefficient matrix. Through the application of designs for shimming planar coils, it is demonstrated that the method can converge to obtain high-precision stream-function parameters that meet the specified profile requirements, even when faced with an unprecedented sharp reduction in the number of target-field points. The method proves to be a promising avenue for expanding design and application scenarios, subverting the limitations of traditional stream-function methods.

Many works in elasticity have exploited the concept of gradient-index (GRIN) lenses, borrowed from optics, for wave focusing and control. These effects are particularly attractive for cloaking, absorption, or energy-harvesting applications. Despite their potential, current lens designs suffer from limitations, mainly related to the difficulty of imaging pointlike sources. Here, we exploit an alternative GRIN lens design that enables a one-to-one correspondence between input and output phase and allows the focal length to be determined using the well-known thin-lens equation, effectively establishing an elastic equivalent of the convex lens in optics. This is demonstrated analytically, obtaining a bijective relation between the location of a pointlike source and its image. The results are also confirmed numerically and experimentally in an aluminum plate, in which the lens is realized by introducing rows of circular cavities of variable diameter. Moreover, a proof-of-concept experiment demonstrates the possibility of imaging sources of flexural waves at the centimeter scale with subwavelength resolution. This research can extend applications of elastic GRIN lenses to new fields such as imaging and nondestructive testing, in which the locations of defects can be identified by focusing the scattered field. Multiple sources can be imaged simultaneously, and the combined effects of multiple lenses can also be used to design more complex systems, opening new possibilities for the technological exploitation of elastic wave manipulation.

Combustion instabilities are one of the primary concerns in a combustion system. Acoustic resonators are used as passive dampers to suppress these instabilities. In the present work, we describe the design, fabrication, and testing of an ultrathin broadband acoustic absorber to dampen the instabilities. The design consists of a series-parallel combination of quarter-wave resonators wrapped like a coiled thin shell around the outer wall of the combustor. The proposed structure is optimized through numerical simulation to improve its performance across the 100–200-Hz frequency band. Numerical and analytical investigations are conducted to examine the impact of turbulent flow with a low Mach number. Experiments are performed for the no-flow, no-heat-source case to validate the analytical and numerical results.

Superconducting circuits with nonlinear elements such as Josephson tunnel junctions or kinetic inductance nanowires are the workhorse for microwave quantum and superconducting sensing technologies. For devices, which can be operated at high temperatures and large magnetic fields, nanoconstrictions as nonlinear elements are recently under intense investigation. Constrictions, however, are far less understood than conventional Josephson tunnel junctions, and their current-phase relationships (CPRs), although key for device design, are hard to predict. Here, we present a niobium microwave cavity with a monolithically integrated, neon-ion-beam patterned three-dimensional (3D) nanoconstriction. By design, we obtain a dc-current-tunable microwave circuit and characterize how the bias-current-dependent constriction properties impact the cavity resonance. Based on the results of these experiments, we reconstruct the CPR of the nanoconstriction. Finally, we discuss the Kerr nonlinearity of the device, a parameter essential for many high-dynamic-range applications and an experimental probe for the second and third derivatives of the CPR. Our platform provides a useful method to comprehensively characterize nonlinear elements integrated in microwave circuits and could be of interest for current sensors, hybrid quantum systems, and parametric amplifiers. Our findings furthermore contribute to a better understanding of nanofabricated 3D constrictions.