Showing papers in "Physical review applied in 2021"
TL;DR: This work shows the applicability of CD driving to enhance the digitized adiabatic quantum computing paradigm in terms of fidelity and total simulation time, and implements this proposal in the IBM quantum computer.
Abstract: Shortcuts to adiabaticity are well-known methods for controlling the quantum dynamics beyond the adiabatic criteria, where counterdiabatic (CD) driving provides a promising means to speed up quantum many-body systems. In this work, we show the applicability of CD driving to enhance the digitized adiabatic quantum computing paradigm in terms of fidelity and total simulation time. We study the state evolution of an Ising spin chain using the digitized version of the standard CD driving and its variants derived from the variational approach. We apply this technique in the preparation of Bell and Greenberger-Horne-Zeilinger states with high fidelity using a very shallow quantum circuit. We implement this proposal on the IBM quantum computer, proving its usefulness for the speed up of adiabatic quantum computing in noisy intermediate-scale quantum devices.
62 citations
TL;DR: This work extends the scenario, where each computation process, being either digital or analog, is described by a continuous time evolution, and shows an improvement of simulation accuracy by two orders, and concludes the feasibility of accurate quantum computing with NISQ devices.
Abstract: Quantum error mitigation (QEM) is vital for noisy intermediate-scale quantum (NISQ) devices. While most conventional QEM schemes assume discrete gate-based circuits with noise appearing either before or after each gate, the assumptions are inappropriate for describing realistic noise that may have strong gate dependence and complicated nonlocal effects, and general computing models such as analog quantum simulators. To address these challenges, we first extend the scenario, where each computation process, being either digital or analog, is described by a continuous time evolution. For noise from imperfections of the engineered Hamiltonian or additional noise operators, we show it can be effectively suppressed by a stochastic QEM method. Since our method assumes only accurate single qubit controls, it is applicable to all digital quantum computers and various analog simulators. Meanwhile, errors in the mitigation procedure can be suppressed by leveraging the Richardson extrapolation method. As we numerically test our method with various Hamiltonians under energy relaxation and dephasing noise and digital quantum circuits with additional two-qubit crosstalk, we show an improvement of simulation accuracy by 2 orders. We assess the resource cost of our scheme and conclude the feasibility of accurate quantum computing with NISQ devices.
60 citations
TL;DR: In this article, a flexible quantum generative adversarial network (GAN) is proposed to learn and generate images of real-world handwritten numerals, and exhibits competitive performance with classical GANs.
Abstract: Quantum machine learning is expected to be among the first practical applications of near-term quantum devices. Whether quantum generative adversarial networks (quantum GANs) implemented on near-term devices can actually solve real-world learning tasks, however, has remained unclear. The authors narrow this knowledge gap by designing a flexible quantum GAN scheme, and realizing this scheme on a superconducting quantum processor. Their system learns and generates images of real-world handwritten numerals, and exhibits competitive performance with classical GANs. This work opens up an avenue for exploring quantum advantage in various machine-learning tasks.
58 citations
TL;DR: This work compares empirical results from the D-Wave 2000Q quantum annealer to the computational ground truth for a variety of portfolio optimization instances and identifies control variations that yield optimal performance in terms of probability of success and probability of chain breaks.
Abstract: Quantum annealing offers an approach to finding the optimal solutions for a variety of computational problems, where the quantum annealing controls influence the observed performance and error mechanisms by tuning the underlying quantum dynamics. However, the influence of the available controls is often poorly understood, and methods for evaluating the effects of these controls are necessary to tune quantum computational performance. Here we use portfolio optimization as a case study by which to benchmark quantum annealing controls and their relative effects on computational accuracy. We compare empirical results from the D-Wave $2000{\mathrm{Q}}^{\mathrm{TM}}$ quantum annealer to the computational ground truth for a variety of portfolio optimization instances. We evaluate both forward and reverse annealing methods and we identify control variations that yield optimal performance in terms of probability of success and probability of chain breaks.
57 citations
TL;DR: In this paper, the authors used a fluorescence-based registration scheme to experimentally determine upper bounds on the cross sections for six fluorophores, including Rhodamine 6G and 9R-S.
Abstract: Excitation with entangled photon pairs may lead to an increase in the efficiency of two-photon absorption at low photon flux. The corresponding process, entangled two-photon absorption (E2PA), has been investigated in numerous theoretical and experimental studies. However, significant ambiguity and inconsistency remain in the literature about the absolute values of E2PA cross sections. Here, we use a fluorescence-based registration scheme to experimentally determine upper bounds on the cross sections for six fluorophores. These bounds are up to 4 orders of magnitude lower than the smallest published cross section. For two samples that have been studied by others, Rhodamine 6G and 9R-S, we measure upper bounds 4 and 5 orders of magnitude lower than the previously reported cross sections.
56 citations
TL;DR: In this paper, diffractive deep neural networks (DNNs) have been used for all-optical signal processing of VBs by configuring the phase and amplitude distribution of diffractive screens.
Abstract: Vortex beams (VBs), possessing a helical phase front and carrying orbital angular momentum (OAM), have attracted considerable attention in optical communications for their mode orthogonality. A platform for achieving all-optical signal processing of VBs, however, remains elusive due to the limited light-field-manipulation capability. We introduce diffractive deep neural networks (${\mathrm{D}}^{2}$NNs) and their applications to process VBs. Exploiting the multiple-light-field-modulation ability of multilayer diffraction structures and the strong data-processing capability of deep neural networks, we reveal that ${\mathrm{D}}^{2}$NNs can manipulate multiple VBs by configuring the phase and amplitude distribution of diffractive screens. The diffraction efficiency and converted-mode purity are greater than 96%. After being trained, ${\mathrm{D}}^{2}$NNs with functions of hybrid-OAM-mode generation, identification, and conversion are obtained, and three typical types of all-optical signal-processing communication, (OAM-shift keying (OAM-SK), OAM multiplexing and demultiplexing, and OAM-mode switching) are successfully achieved. Our simulation results provide an approach that breaks the limitations of poor functionality and complex design in processing VBs, introducing the ${\mathrm{D}}^{2}$NN as a universal light-field-modulation platform.
53 citations
TL;DR: This paper introduces an approach to simplify state preparation, together with a circuit optimization technique, both of which can help reduce the circuit complexity for QAE state preparation significantly.
Abstract: Quantum amplitude estimation (QAE) can achieve a quadratic speedup for applications classically solved by Monte Carlo simulation. A key requirement to realize this advantage is efficient state preparation. If state preparation is too expensive, it can diminish the quantum advantage. Preparing arbitrary quantum states has exponential complexity with respect to the number of qubits, and thus, is not applicable. Currently known efficient techniques require problems based on log-concave probability distributions, involve learning an unknown distribution from empirical data, or fully rely on quantum arithmetic. In this paper, we introduce an approach to simplify state preparation, together with a circuit optimization technique, both of which can help reduce the circuit complexity for QAE state preparation significantly. We demonstrate the introduced techniques for a numerical integration example on real quantum hardware, as well as for option pricing under the Heston model, i.e., based on a stochastic volatility process, using simulation.
50 citations
TL;DR: In this paper, the authors theoretically proposed a switching device that operates at room temperature, which is an in-plane heterostructure based on a periodically boron-doped (nitrogen-decomposed) armchair graphene nanoribbon, which has been experimentally fabricated recently.
Abstract: We theoretically propose a switching device that operates at room temperature. The device is an in-plane heterostructure based on a periodically boron-doped (nitrogen-doped) armchair graphene nanoribbon, which has been experimentally fabricated recently. The calculated $I$-$V$ curve shows that for a realistic device with interface width longer than $20$ nm, nonzero electric current occurs only in the region of bias voltage between $\ensuremath{-}0.22$ and $0.28$ V, which is beneficial to low-voltage operation. Furthermore, in this case, the electric current is robust against the change of the potential profile in the interface since the metallic impurity-induced sub-bands with delocalized wave functions contribute to the transmission exclusively. This also suggests the high response speed of the proposed device. We also discuss the temperature dependence, the output impedance, the effect of phonons, and the possible regimes to extend our work, which suggest that our model may have potential room-temperature nanoelectronics applications.
49 citations
TL;DR: In this paper, the authors extend the concept to boost noise mitigation with an external drive, yielding $d\phantom{\rule{0}{0ex}}y \phantom{0,0ex}n\phant{0,0ex]m\phant {0, 0ex}c\phanto{0}, 0, 0, l$ sweet spots and turning static sweet spots into manifolds.
Abstract: Superconducting qubits provide a promising architecture for scalability in quantum information processing, but their coherence times are currently limited by environmental noise, miring such processors in the noisy intermediate-scale regime. Operating at ``sweet spots'' (turning points in a qubit's microwave spectrum) can substantially reduce the dephasing due to $1/f$ flux noise. The authors extend this concept to boost noise mitigation with an external drive, yielding $d\phantom{\rule{0}{0ex}}y\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}m\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l$ sweet spots and turning static sweet ``spots'' into manifolds. This simple, powerful approach adds flexibility to the choice of operating points, and could enhance coherence times by more than an order of magnitude.
44 citations
TL;DR: In this paper, a line of gradient resonant pillars for robust subwavelength focusing and imaging of elastic waves in a plate was proposed, and the authors showed that the enhanced focusing resolution with smaller FWHM can be very beneficial for energy harvesting since the output electric power can be increased by an order of magnitude.
Abstract: Metasurfaces are planar metamaterials with a flat surface and a subwavelength thickness that are able to shape arbitrary wave fronts such as focusing or imaging. There is a broad interest in the literature about subwavelength focusing and imaging based on bulk metamaterials while the utilization of metasurfaces for elastic waves has rarely been reported. Here, we present a type of elastic metasurface consisting of a line of gradient resonant pillars for robust deep subwavelength focusing and imaging of elastic waves in a plate. Numerical approaches supported by analytic Huygens-Fresnel demonstrations show that the subwavelength full width at half maximum (FWHM) behaves linearly as a function of the ratio F/D where F is the measured focal length and D the metasurface length. We discuss the range of F/D where FWHM remains smaller than half a wavelength in the near field. The focal length F and the FWHM exhibit stable performances when submitted to disorder perturbations in the geometrical parameters and to frequency fluctuations. We show that the enhanced focusing resolution with smaller FWHM can be very beneficial for energy harvesting since the output electric power can be increased by more than one order of magnitude. The proposed elastic metasurfaces bring a way for high resolution focusing and imaging which is useful for applications in various domains such as energy harvesting, wave sensing, communication, nondestructive evaluation.
37 citations
TL;DR: In this paper, the authors realized a membrane-based scanning force microscope and demonstrated nanometer-scale topographic imaging, which is a promising candidate for quantum-limited force detection, and for nuclear spin imaging.
Abstract: Mechanical resonators based on silicon nitride membranes offer very high quality factors and outstanding force sensitivity. However, applying such devices as practical sensors has long been impeded by their seemingly incompatible clamping geometry. Using an unconventional setup, the authors realize a membrane-based scanning force microscope and demonstrate nanometer-scale topographic imaging. This instrument is a promising candidate for quantum-limited force detection, and for nuclear spin imaging.
TL;DR: A methodology to combine these tools to find a quantitatively accurate system model, high-fidelity gates and an approximate error budget, all based on a high-performance, feature-rich simulator are presented.
Abstract: Efforts to scale-up quantum computation have reached a point where the principal limiting factor is not the number of qubits, but the entangling gate infidelity. However, the highly detailed system characterization required to understand the underlying error sources is an arduous process and impractical with increasing chip size. Open-loop optimal control techniques allow for the improvement of gates but are limited by the models they are based on. To rectify the situation, we provide an integrated open-source tool set for control, calibration, and characterization (${\mathbb{C}}^{3}$), capable of open-loop pulse optimization, model-free calibration, model fitting, and refinement. We present a methodology to combine these tools to find a quantitatively accurate system model, high-fidelity gates, and an approximate error budget, all based on a high-performance, feature-rich simulator. We illustrate our methods using simulated fixed-frequency superconducting qubits for which we learn model parameters with less than $1\mathrm{%}$ error and derive a coherence-limited cross-resonance gate that achieves $99.6\mathrm{%}$ fidelity without the need for calibration.
TL;DR: Based on a photonic dimer chain composed of ultrasubwavelength resonators, the TEM in the effective second-order parity-time (PT) system is immune to the inner disorder perturbation, and can be used to realize the long-range wireless power transfer (WPT) with high transmission efficiency.
Abstract: Topological characteristics, including invariant topological orders, band inversion, and the topological edge mode (TEM) in photonic insulators, have been widely studied. Whether intriguing topological modes can be taken advantage of in simple one-dimensional systems to implement some practical applications is an issue, which is of increasing concern. In this work, based on a photonic dimer chain composed of ultrasubwavelength resonators, we verify experimentally that the TEM in the effective second-order parity-time (PT) system is immune to the inner disorder perturbation, and can be used to realize the long-range wireless power transfer (WPT) with high transmission efficiency. To intuitively show the TEM can be used for WPT, a power signal source is used to excite the TEM. It can be clearly seen that two light-emitting diode (LED) lamps with 0.5 W at both ends of the structure are lit up with the aid of TEMs. In addition, in order to solve the special technical problems of standby power loss and frequency tracking, we further propose that a WPT system with effective third-order PT symmetry can be constructed by using one topological interface mode and two TEMs. Inspired by the long-range WPT with TEMs in this work, the use of more complex topological structures is expected to achieve energy transmission with more functions, such as the WPT devices whose direction can be selected flexibly in the quasiperiodic or trimer topological chains.
TL;DR: In this article, the authors demonstrate high-sensitivity N-$V$-ensemble-based magnetic field measurements with low-intensity optical excitation using a diamond magnetometer, achieving a minimum detectable field of 0.3-0.7 pT in a 73-s measurement when a flux guide with a sensing dimension of 2 mm is applied.
Abstract: Nitrogen-vacancy (N-$V$) centers in diamond have developed into a powerful solid-state platform for compact quantum sensors. However, high-sensitivity measurements usually come with additional constraints on the pumping intensity of the laser and the pulse control applied. Here, we demonstrate high-sensitivity N-$V$-ensemble-based magnetic field measurements with low-intensity optical excitation. Direct current magnetometry methods such as continuous-wave optically detected magnetic resonance and continuously excited Ramsey measurements combined with lock-in detection are compared to achieve an optimization. Gradiometry is also investigated as a step towards unshielded measurements of unknown gradients. The magnetometer demonstrates a minimum detectable field of 0.3--0.7 pT in a 73-s measurement when a flux guide with a sensing dimension of 2 mm is applied, corresponding to a magnetic field sensitivity of 2.6--6 $\mathrm{pT}/\sqrt{\mathrm{Hz}}$. Combined with our previous efforts on diamond ac magnetometry, the diamond magnetometer is promising for performing wide-bandwidth magnetometry with picotesla sensitivity and a cubic-millimeter sensing volume under ambient conditions.
TL;DR: In this paper, the authors present an analytic framework for the homogenization theory of space-time metamaterials, and yield physical insight into their behavior, including regimes of nonreciprocity and conditions for huge effective bianisotropy.
Abstract: The theory of homogenization of material parameters has been a cornerstone in the development of metamaterials. The conventional framework, however, is not applicable to the $s\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}m\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l$ metamaterials that give access to additional wave phenomena, thanks to properties tailored not only in space but also in time. This study presents an analytic framework for the homogenization theory of space-time metamaterials, and yields physical insight into their behavior, including regimes of nonreciprocity and conditions for huge effective bianisotropy. This approach also deepens our understanding of the connections between space-time modulations and moving matter.
TL;DR: This work introduces a protocol that uses mutliple subspaces of the high-dimensional system simultaneously to exploit noisy entanglement of spatio-temporal degrees of freedom of single photons and can be used to increase key rates in realistic conditions.
Abstract: High-dimensional entanglement promises to increase the information capacity of photons and is now routinely generated, exploiting spatiotemporal degrees of freedom of single photons. A curious feature of these systems is the possibility of certifying entanglement despite strong noise in the data. We show that it is also possible to exploit this noisy high-dimensional entanglement for quantum key distribution by introducing a protocol that uses multiple subspaces of the high-dimensional system simultaneously. Our protocol can be used to establish a secret key even in extremely noisy experimental conditions, where qubit protocols fail. To show that, we analyze the performance of our protocol for noise models that apply to the two most commonly used sources of high-dimensional entanglement: time bins and spatial modes.
TL;DR: In this article, a tunable acoustic metasurface composed of Helmholtz-resonator-like digital-coding meta-atoms is presented to overcome the limitation and realize 3D dynamic wave manipulations.
Abstract: Acoustic metasurfaces display unprecedented potential for their unique and flexible capabilities of wave front manipulations. Although rapid progress and significant developments have been achieved in this field, it still remains a significant challenge to obtain an acoustic metasurface that can perform different functions in three-dimensional (3D) space, as desired. Here, a tunable acoustic metasurface composed of Helmholtz-resonator-like digital-coding meta-atoms is presented to overcome the limitation and realize 3D dynamic wave manipulations. The digital meta-atom is constructed from two cylindrical cavities controlled by a motor. By changing the depth of the bottom cavity with the motor automatically, the reflection phase of the meta-atom can be adjusted continuously over the range of nearly 360\ifmmode^\circ\else\textdegree\fi{}, realizing the required digital states. To build the relationship between the digital-coding profiles and scattering patterns, convolution and addition operations are implemented. Based on such operations, various fascinating functionalities, such as arbitrary scattering-pattern shift and superposition of different scattering beams, are achieved. This study paves the way for studying acoustic metasurfaces from the digital perspective and provides efficient methods for realizing spatial acoustic wave control.
TL;DR: In this article, a noise-assisted quantum-autoencoder algorithm was proposed to achieve high recovering fidelity for general input states, where appropriate noise channels were used to make the input mixedness and output mixedness consistent.
Abstract: Quantum autoencoder is an efficient variational quantum algorithm for quantum data compression. However, previous quantum autoencoders fail to compress and recover high-rank mixed states. In this work, we discuss the fundamental properties and limitations of the standard quantum-autoencoder model in more depth, and provide an information-theoretic solution to its recovering fidelity. Based on this understanding, we present a noise-assisted quantum-autoencoder algorithm to go beyond the limitations, our model can achieve high recovering fidelity for general input states. Appropriate noise channels are used to make the input mixedness and output mixedness consistent, the noise setup is determined by measurement results of the trash system. Compared with the original quantum-autoencoder model, the measurement information is fully used in our algorithm. In addition to the circuit model, we design a (noise-assisted) adiabatic model of quantum autoencoder that can be implemented on quantum annealers. We verify the validity of our methods through compressing the thermal states of the transverse-field Ising model and Werner states. For pure-state ensemble compression, we also introduce a projected quantum-autoencoder algorithm.
TL;DR: In this paper, the authors show that the steering directivity only depends on the ratio of two coupling rates and is barely affected by the dissipation of the system, while the entanglement and steering can be significantly enhanced due to the squeezed vacuum field and thus are more robust against thermal noises.
Abstract: We show how to implement stationary one-way quantum steering with strong entanglement in a cavity magnonic system that consists of two magnon modes and a microwave cavity. The cavity is driven by a squeezed vacuum field generated by a flux-driven Josephson parameter amplifier and coupled to two Kittel modes via magnetic dipole interaction. We find that the steering directivity only depends on the ratio of two coupling rates (i.e., the ratio of coherent information exchange frequencies) and is barely affected by the dissipation of the system. Meanwhile, the entanglement and steering can be significantly enhanced due to the squeezed vacuum field and thus are more robust against thermal noises. This provides an active method to manipulate the steering directivity instead of adding asymmetric losses or noises to subsystems at the cost of reducing steerability.
TL;DR: In this article, Niobium resonators after removing native oxides by HF etching were shown to yield a quality factor of $7.5$ in the single-photon limit, where Nb is the only surface oxide that grows significantly in the first week.
Abstract: To improve the performance of state-of-the-art superconducting quantum devices, microwave loss due to defects at amorphous interfacial layers must be reduced, via proper surface treatment. The authors study niobium resonators after removing native oxides by HF etching, which reduces losses about tenfold and yields a quality factor of $7\ifmmode\times\else\texttimes\fi{}{10}^{6}$ in the single-photon limit. Losses reappear as oxides form upon exposure to air; Nb${}_{2}$O${}_{5}$ is the only surface oxide that grows significantly in the first week. These findings are of interest for a panoply of devices, inluding superconducting qubits, quantum-limited amplifiers, microwave kinetic-inductance detectors, and single-photon detectors.
TL;DR: In this paper, the authors proposed an ultrabroadband ventilation barrier via hybridization of dissipation and interference, which significantly expands the range of the operating frequencies, enabling an effective blocking of more than $90\mathrm{%}$ of incident energy in the range from $650$ to $2000\phantom{\rule{0.2em}{0ex}}\mathm{Hz}$, while its structural thickness is only $53
Abstract: Ventilation barriers allowing simultaneous sound blocking and free airflow passage are a great challenge but are necessary for particular scenarios calling for soundproofing ventilation. Previous studies using local resonance or Fano-like interference consider a narrow working range around the resonant or destructive-interference frequency. Efforts made with regard to broadband designs show a limited bandwidth typically smaller than half an octave. Here we conceptually propose an ultrabroadband ventilation barrier via hybridization of dissipation and interference. Confirmed by experiments, our hybrid-functional metasurface, empowered by its synergistic effect, significantly expands the range of the operating frequencies, enabling an effective blocking of more than $90\mathrm{%}$ of incident energy in the range from $650$ to $2000\phantom{\rule{0.2em}{0ex}}\mathrm{Hz}$, while its structural thickness is only $53\phantom{\rule{0.2em}{0ex}}\mathrm{mm}$ (approximately $\ensuremath{\lambda}/10)$. Our design showcases the great flexibility of customizing the broadband and is capable of tackling sound coming from various directions, which has potential in air-permeable yet soundproofing applications.
TL;DR: In this paper, a two-dimensional triangular-lattice phononic crystal with Ω(C}_{3v}$-symmetric scatterers was constructed, and two distinct valley Hall phases with nonvanishing valley Chern indices were obtained by rotating the scatterer.
Abstract: Valley interface states, resulting in acoustic valley Hall topological insulators, have recently become a hot topic in the study of acoustic systems. On the basis of structural diversity and potential applications, we construct a two-dimensional triangular-lattice phononic crystal with ${C}_{3v}$-symmetric scatterers, and obtain two distinct valley Hall phases with nonvanishing valley Chern indices by rotating the scatterers. We numerically calculate the dispersion relations of these valley Hall phases including two kinds of interfaces, and find that valley interface states exist at not only the zigzag interface but also the armchair interface. We demonstrate the acoustic splitting and merging of valley interface states in the cross-waveguides, and numerically achieve the xor and or logic functions. We also design three complicated waveguides by assembling phononic crystals with distinct valley Hall phases. By experimental measurements in these waveguides, we successfully implement one-, two-, and three-channel topological transport. This research possibly provides a design route exploiting valley interface states to fabricate multichannel acoustic communication devices.
TL;DR: In this article, a stereoscopic multilayered ultrabroadband metamaterial absorber by stacking multilayer concentric resonators on different-level top surfaces of a monolithic three-dimensional (3D) pagodalike substrate was proposed.
Abstract: Terahertz (THz) absorbers have recently attracted extensive attention for their promising potential in various applications; however, many existing THz absorbers are restrained by their narrow bandwidth and complicated and costly fabrication process that renders them unfavorable for practical devices. Herein, we propose a stereoscopic multilayered ultrabroadband THz metamaterial absorber by stacking multilayer concentric resonators on different-level top surfaces of a monolithic three-dimensional (3D) pagodalike substrate. By taking full advantage of the 3D printing technique, the proposed ultrabroadband absorber can be produced efficiently in an easy three-step process that overcomes the fabrication complexities of traditional multistep photolithography processes. Additionally, the feasibility and robustness of the proposed fabrication method for common out-of-plane THz narrowband absorbers are also validated, and the absorption capacities of the 3D printed absorbers are numerically and experimentally elucidated. These results might provide an efficient concept and fabrication technique to stimulate many potential applications in emerging THz technologies, such as sensing, imaging, and wireless communications.
TL;DR: In this article, a wave-mode conversion and rainbow trapping in an elastic waveguide loaded with an array of resonators is demonstrated. But the wave-speed reduction with a reflection mechanism is not considered.
Abstract: We experimentally achieve wave-mode conversion and rainbow trapping in an elastic waveguide loaded with an array of resonators. Rainbow trapping is a phenomenon that induces wave confinement as a result of a spatial variation of the wave velocity, here promoted by gently varying the length of consecutive resonators. By breaking the geometrical symmetry of the waveguide, we combine the wave-speed reduction with a reflection mechanism that mode converts flexural waves impinging on the array into torsional waves traveling in opposite directions. The framework presented herein may open opportunities in the context of wave manipulation through the realization of structural components with concurrent wave-conversion and energy-trapping capabilities.
TL;DR: In this paper, the interaction of surface acoustic waves (SAWs) with spin waves (SWs) in a piezoelectric-ferromagnetic hybrid device was studied.
Abstract: We study the interaction of surface acoustic waves (SAWs) with spin waves (SWs) in a ${\mathrm{Co}}_{40}{\mathrm{Fe}}_{40}{\mathrm{B}}_{20}$/$\mathrm{Au}$/${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ system composed of two ferromagnetic layers separated by a nonmagnetic $\mathrm{Au}$ spacer layer. Because of interlayer magnetic dipolar coupling between the two ferromagnetic layers, a symmetric and an antisymmetric SW mode form, which both show a highly nondegenerate dispersion relation for oppositely propagating SWs. Due to magnetoacoustic SAW-SW interaction, we observe highly nonreciprocal SAW transmission in the piezoelectric-ferromagnetic hybrid device. We experimentally and theoretically characterize the magnetoacoustic wave propagation as a function of frequency, wave vector, and external magnetic field magnitude and orientation. Additionally, we demonstrate that the nonreciprocal SW dispersion of a coupled magnetic bilayer is highly tuneable and not limited to ultrathin magnetic films, in contrast to the nonreciprocity induced by the interfacial Dzyaloshinskii-Moriya interaction. Therefore, magnetoacoustic coupling in ferromagnetic multilayers provides a promising route towards building efficient acoustic isolators.
TL;DR: In this article, the performance limits of n-and p-type sub-5-nm monolayer (ML) MOSFETs were investigated and it was shown that the optimized on-state currents can reach up to 1390 and 1025 µm for high-performance and low-power (LP) applications, respectively, which satisfy the International Technology Roadmap for Semiconductors (ITRS) requirements.
Abstract: Two-dimensional (2D) semiconductors have attracted tremendous interest as natural passivation and atomically thin channels could facilitate continued transistor scaling. However, air-stable 2D semiconductors with high performance are quite elusive. Recently, an extremely-air-stable ${\mathrm{Mo}\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ monolayer was successfully fabricated [Hong et al., Science 369, 670 (2020)]. To further reveal its potential application in sub-5-nm metal-oxide-semiconductor field-effect transistors (MOSFETs), there is an urgent need to develop integrated circuits. Here, we report first-principles quantum-transport simulations on the performance limits of n- and p-type sub-5-nm monolayer (ML) ${\mathrm{Mo}\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ MOSFETs. We find that the on-state current in the ${\mathrm{Mo}\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ MOSFETs can be effectively manipulated by the length of gate and underlap, as well as the doping concentration. Very strikingly, we also find that for the n-type devices the optimized on-state currents can reach up to 1390 and 1025 \textmu{}A/\textmu{}m for high-performance and low-power (LP) applications, respectively, both of which satisfy the International Technology Roadmap for Semiconductors (ITRS) requirements. The optimized on-state current can meet the LP application (348 \textmu{}A/\textmu{}m) for p-type devices. Finally, we find that the ${\mathrm{Mo}\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ MOSFETs have an ultralow subthreshold swing and power-delay product, which have the potential to realize high-speed and low-power consumption devices. Our results show that ${\mathrm{Mo}\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ is an ideal 2D channel material for future competitive ultrascaled devices.
TL;DR: In this paper, a two-dimensional crystalline perforated elastic plate, using a square lattice that hosts symmetry-induced topological edge states was designed to control and redirect elastic waves.
Abstract: We combine two different fields, topological physics and graded metamaterials, to design a topological metasurface to control and redirect elastic waves. We strategically design a two-dimensional crystalline perforated elastic plate, using a square lattice, that hosts symmetry-induced topological edge states. By concurrently allowing the elastic substrate to spatially vary in depth, we are able to convert the incident slow wave into a series of robust modes, with differing envelope modulations. This adiabatic transition localizes the incoming energy into a concentrated region where it can then be damped or extracted. For larger transitions, different behavior is observed; the incoming energy propagates along the interface before being partitioned into two disparate chiral beams. This ``topological rainbow'' effect leverages two main concepts, namely the quantum valley Hall effect and the rainbow effect usually associated with electromagnetic metamaterials. The topological rainbow effect transcends specific physical systems; hence, the phenomena we describe can be transposed to other wave physics. Because of the directional tunability of the elastic energy by geometry, our results have potential for applications such as switches, filters, and energy harvesters.
TL;DR: This work introduces a simple and practical measurement-device-independent (MDI) QKD type of protocol, based on the transmission of coherent light, for which it is proved its security against any possible device imperfection and/or side-channel at the transmitters' side.
Abstract: There is a large gap between theory and practice in quantum key distribution (QKD) because real devices do not satisfy the assumptions required by the security proofs. Here, we close this gap by introducing a simple and practical measurement-device-independent-QKD type of protocol, based on the transmission of coherent light, for which we prove its security against any possible imperfection and/or side channel from the quantum communication part of the QKD devices. Our approach only requires to experimentally characterize an upper bound of one single parameter for each of the pulses sent, which describes the quality of the source. Moreover, unlike device-independent (DI) QKD, it can accommodate information leakage from the users' laboratories, which is essential to guarantee the security of QKD implementations. In this sense, its security goes beyond that provided by DI QKD, yet it delivers a secret key rate that is various orders of magnitude greater than that of DI QKD.
TL;DR: In this article, a direct gradiometer using optical pumping with opposite circular polarization in two atomic ensembles within a single multipass cell is described, and a far-detuned probe laser undergoes a near-zero paramagnetic Faraday rotation due to the intrinsic subtraction of two contributions exceeding 3.5 rad from the highly polarized enassembles.
Abstract: We describe a direct gradiometer using optical pumping with opposite circular polarization in two ${}^{87}\mathrm{Rb}$ atomic ensembles within a single multipass cell. A far-detuned probe laser undergoes a near-zero paramagnetic Faraday rotation due to the intrinsic subtraction of two contributions exceeding 3.5 rad from the highly polarized ensembles. We develop analysis methods for the direct gradiometer signal and measure a gradiometer sensitivity of 10.1 $\mathrm{fT}/\mathrm{cm}\sqrt{\mathrm{Hz}}$. We also demonstrate that our multipass design, in addition to increasing the optical depth, provides a fundamental advantage due to the significantly reduced effect of atomic diffusion on the spin-noise time-correlation, in excellent agreement with the theoretical estimate.