Electrically tunable on-chip quantum Deutsch-Jozsa algorithm with lithium niobate metasurfaces.

Owing to the inherent advantages of parallelism, rapid processing speed, and minimal energy consumption, optical analog computing has witnessed a progressive development. Quantum optical computing exceeds the capabilities of classical computing in terms of computational speed in numerous tasks. However, existing metamaterial-based quantum Deutsch-Jozsa (DJ) algorithm devices have large structural dimensions and are not suitable for miniaturized optical computing systems. Furthermore, most reported on-chip metasurface devices, rendered monofunctional after fabrication, do not possess sophisticated optical systems. In this work, we develop an electrically tunable on-chip DJ algorithm device on a lithium-niobate-on-insulator (LNOI) platform. The on-chip device consists of various etched slots, each with carefully designed size. By applying different external voltages to each individual unit, precise phase redistribution across the device is attainable, enabling the realization of tunable DJ algorithm. Notably, we can determine whether the oracle metasurface yields a constant or balance function by measuring the output electric field. The on-chip device is miniaturized and easy to integrate while enabling functional reconfiguration, which paves the way for numerous applications in optical computing.

Interlayer coupled dual-layer metagratings for broadband and high-efficiency anomalous reflection.

Recent progress in metagratings highlights the promise of high-performance wavefront engineering devices, notably for their exterior capability to steer beams with near-unitary efficiency. However, the narrow operating bandwidth of conventional metagratings remains a significant limitation. Here, we propose and experimentally demonstrate a dual-layer metagrating, incorporating enhanced interlayer couplings to realize high-efficiency and broadband anomalous reflection within the microwave frequency band. The metagrating facilitated by both intralayer and interlayer couplings is designed through the combination of eigenmode expansion (EME) algorithm and particle swarm optimization (PSO) to significantly streamline the computational process. Our metagrating demonstrates the capacity to reroute a normally incident wave to +1 order diffraction direction across a broad spectrum, achieving an average efficiency approximately 90% within the 14.7 to 18 GHz range. This study may pave the way for future applications in sophisticated beam manipulations, including spatial dispersive devices, by harnessing the intricate dynamics of multi-layer metagratings with complex interlayer and intralayer interactions.

Experimental Demonstration of Controllable PT and Anti-PT Coupling in a Non-Hermitian Metamaterial.

Non-Hermiticity has recently emerged as a rapidly developing field due to its exotic characteristics related to open systems, where the dissipation plays a critical role. In the presence of balanced energy gain and loss with environment, the system exhibits parity-time (PT) symmetry, meanwhile as the conjugate counterpart, anti-PT symmetry can be achieved with dissipative coupling within the system. Here, we demonstrate the coherence of complex dissipative coupling can control the transition between PT and anti-PT symmetry in an electromagnetic metamaterial. Notably, the achievement of the anti-PT symmetric phase is independent of variations in dissipation. Furthermore, we observe phase transitions as the system crosses exceptional points in both anti-PT and PT symmetric metamaterial configurations, achieved by manipulating the frequency and dissipation of resonators. This work provides a promising metamaterial design for broader exploration of non-Hermitian physics and practical application with a controllable Hamiltonian.

Editorial for the Special Issue on Tunable Nanophotonics and Reconfigurable Metadevices.

Photonic nano/microstructures (e [...].

High-efficiency modulation of broadband polarization conversion with a reconfigurable chiral metasurface.

We demonstrate an electrically biased reconfigurable chiral metasurface for controlling the polarization conversion and asymmetric transmission in a broadband manner. The reconfigurable metasurface is constructed with coupled three-layer complementary split-ring resonator (CSRR) arrays and is loaded with tunable electronic components to achieve dynamic control of reconfigurable chiral coupling in the CSRRs by simply tuning the external voltage on the structure. It is found that the polarization conversion in the metasurface can be effectively and continuously tuned in both experiments and simulations in a broadband frequency range. Meanwhile, the reconfigurable metasurface shows an asymmetric transmission (AT) effect in a broadband range for a polarized wave. The proposed reconfigurable chiral metasurface based on the active tuning of connection in the meta-structure with few functional layers is confirmed as an effective strategy for multi-functional polarization manipulation. The reported broadband properties of the chiral metasurface are promising for polarization manipulation in optical bands and applications in wireless communication.

Improved Black Widow Spider Optimization Algorithm Integrating Multiple Strategies.

The black widow spider optimization algorithm (BWOA) had the problems of slow convergence speed and easily to falling into local optimum mode. To address these problems, this paper proposes a multi-strategy black widow spider optimization algorithm (IBWOA). First, Gauss chaotic mapping is introduced to initialize the population to ensure the diversity of the algorithm at the initial stage. Then, the sine cosine strategy is introduced to perturb the individuals during iteration to improve the global search ability of the algorithm. In addition, the elite opposition-based learning strategy is introduced to improve convergence speed of algorithm. Finally, the mutation method of the differential evolution algorithm is integrated to reorganize the individuals with poor fitness values. Through the analysis of the optimization results of 13 benchmark test functions and a part of CEC2017 test functions, the effectiveness and rationality of each improved strategy are verified. Moreover, it shows that the proposed algorithm has significant improvement in solution accuracy, performance and convergence speed compared with other algorithms. Furthermore, the IBWOA algorithm is used to solve six practical constrained engineering problems. The results show that the IBWOA has excellent optimization ability and scalability.

Photoactive terahertz metasurfaces for ultrafast switchable sensing of colorectal cells.

Metasurfaces with a strongly enhanced local field are envisioned as a powerful platform for ultrasensitive optical sensors to significantly amplify imperceptible differences between compatible bioanalytes. Through the use of phototunable silicon-based terahertz (THz) metasurfaces, we experimentally demonstrate ultrafast switchable sensing functions. It is found that the THz responses of the coupled-resonances in the metasurfaces shift from Lorentz-lattice mode to electromagnetism-induced transparency (EIT) mode under optical pumping within an ultrashort time of 32 ps, enabling an ultrafast sensitive sensor. For the Lorentz-lattice mode, the THz time-domain signal directly shows a highly sensitive response to detect tiny analytes without extra Fourier transformation as the mismatch between the two modes increases. Once the metasurfaces are switched to the EIT mode, the silicon-metal hybrid structure supports frequency-domain sensing ability due to strong field confinement with a sensitivity of 118.4 GHz/RIU. Both of the sensing configurations contribute to more subtle information and guarantee the accuracy of the sensor performance. Combined with the aforementioned advantages, the proposed metasurfaces have successfully identified colorectal cells between normal, adenoma, and cancer states in experiments. This work furnishes a new paradigm of constructing reliable and flexible metasurface sensors and can be extended to other optics applications.

Research on Coverage Optimization in a WSN Based on an Improved COOT Bird Algorithm.

To address the problems of uneven distribution and low coverage of wireless sensor network (WSN) nodes in random deployment, a node coverage optimization strategy with an improved COOT bird algorithm (COOTCLCO) is proposed. Firstly, the chaotic tent map is used to initialize the population, increase the diversity of the population, and lay the foundation for the global search for the optimal solutions. Secondly, the Lévy flight strategy is used to perturb the individual positions to improve the search range of the population. Thirdly, Cauchy mutation and an opposition-based learning strategy are fused to perturb the optimal solutions to generate new solutions and enhance the ability of the algorithm to jump out of the local optimum. Finally, the COOTCLCO algorithm is applied to WSN coverage optimization problems. Simulation results show that COOTCLCO has a faster convergence speed and better search accuracy than several other typical algorithms on 23 benchmark test functions; meanwhile, the coverage rate of the COOTCLCO algorithm is increased by 9.654%, 13.888%, 6.188%, 5.39%, 1.31%, and 2.012% compared to particle swarm optimization (PSO), butterfly optimization algorithm (BOA), seagull optimization algorithm (SOA), whale optimization algorithm (WOA), Harris hawks optimization (HHO), and bald eagle search (BES), respectively. This means that in terms of coverage optimization effect, COOTCLCO can obtain a higher coverage rate compared to these algorithms. The experimental results demonstrate that COOTCLCO can effectively improve the coverage rate of sensor nodes and improve the distribution of nodes in WSN coverage optimization problems.

Fano-Resonant Hybrid Metamaterial for Enhanced Nonlinear Tunability and Hysteresis Behavior.

Artificial resonant metamaterial with subwavelength localized filed is promising for advanced nonlinear photonic applications. In this article, we demonstrate enhanced nonlinear frequency-agile response and hysteresis tunability in a Fano-resonant hybrid metamaterial. A ceramic cuboid is electromagnetically coupled with metal cut-wire structure to excite the high-Q Fano-resonant mode in the dielectric/metal hybrid metamaterial. It is found that the significant nonlinear response of the ceramic cuboid can be employed for realization of tunable metamaterials by exciting its magnetic mode, and the trapped mode with an asymmetric Fano-like resonance is beneficial to achieve notable nonlinear modulation on the scattering spectrum. The nonlinear tunability of both the ceramic structure and the ceramic/metal hybrid metamaterial is promising to extend the operation band of metamaterials, providing possibility in practical applications with enhanced light-matter interactions.

EIA metamaterials based on hybrid metal/dielectric structures with dark-mode-enhanced absorption.

Metamaterial analogue of electromagnetically induced absorption (EIA) has promising applications in spectroscopy and sensing. Here we propose an EIA metamaterial based on hybrid metal/dielectric structures, which are composed of a metallic wire and a dielectric block, and investigate the EIA-like effect by simulations, experiments, and the two-oscillator model. An EIA-like effect emerges in virtue of the near-field coupling between metallic wire and dielectric block, and the dielectric block exhibiting magnetic dipolar resonance makes a major contribution to the resonance absorption. The magnetic flux through the dielectric block engendered by the near filed of the metallic wire determines the coupling between dielectric block and metallic wire. With the variation of the separation between dielectric block and metallic wire, the EIA-like effect is preserved and does not convert into the EIT-like effect although the coupling and consequently the absorbance are altered. Based on the two-oscillator model, the absorption spectrum of the EIA metamaterial is quantitatively analyzed and the parameters of the oscillator system are retrieved.

Simulate Deutsch-Jozsa algorithm with metamaterials.

During the past few years, a lot of efforts have been devoted in studying optical analog computing with artificial structures. Up to now, much of them are primarily focused on classical mathematical operations. How to use artificial structures to simulate quantum algorithm is still to be explored. In this work, an all-dielectric metamaterial-based model is proposed and realized to demonstrate the quantum Deutsch-Jozsa algorithm. The model is comprised of two cascaded functional metamaterial subblocks. The oracle subblock encodes the detecting functions (constant or balanced), onto the phase distribution of the incident wave. Then, the original Hadamard transformation is performed with a graded-index subblock. Both the numerical and experimental results indicate that the proposed metamaterials are able to simulate the Deutsch-Jozsa problem with one round operation and a single measurement of the output eletric field, where the zero (maximum) intensity at the central position results from the destructive (constructive) interference accompanying with the balance (constant) function marked by the oracle subblock. The proposed computational metamaterial is miniaturized and easy-integration for potential applications in communication, wave-based analog computing, and signal processing systems.

Realization of a near-infrared active Fano-resonant asymmetric metasurface by precisely controlling the phase transition of Ge2Sb2Te5.

A metasurface is one of the most effectual platforms for the manipulation of complex optical fields. One of the current challenges in the field is to develop active or reconfigurable functionalities to extend its operation band which is limited by its intrinsic resonant nature. Here we demonstrate a kind of active Fano-resonant asymmetric metasurface in the near-infrared (NIR) region with heterostructures made of a layer of asymmetric split-ring resonators and a thin layer of phase-change material (PCM). In the asymmetric metasurface, significant tunability in the frequency, Q-factor and strength of the Fano resonance are all achieved by precisely controlling the phase transition of the contained PCM Ge2Sb2Te5 (GST), together with changing the geometric asymmetry of the split-ring resonators. Moreover, we provide a complete transition process of the optical properties for GST and an optimized modulation on the active Fano-resonant metasurface. Our approach to dynamically control a Fano-resonant metasurface paves the way to realizing various active photonic meta-devices involving PCM.

Controllable coherent perfect absorber made of liquid metal-based metasurface.

Coherent perfect absorber (CPA) is a novel strategy proposed and demonstrated for solving the challenge to attain efficient control of absorption by exploiting the inverse process of lasing. The operation condition of CPA results in narrow-band, which is the main limitation obstruct it from practical applications. Here, we demonstrate a CPA with tunable operation frequency employing the liquid metal made reconfigurable metasurface. The flow of liquid metal is restricted with a plastic pipe for realizing a controllable liquid metal cut-wire. The adjustable electric dipolar mode of the reconfigurable cur-wire metasurface ensures that the quasi-CPA point can be dynamically controlled; the measured CPA under proper phase modulation is in good agreement with the simulation results. The proposed CPA system involving liquid metal for dynamic control of operation frequency will have potential applications and may stimulate the exploitation of liquid based smart absorption control of optical waves.

Phase-Modulated Scattering Manipulation for Exterior Cloaking in Metal-Dielectric Hybrid Metamaterials.

Artificially structured metamaterials with metallic or dielectric inclusions are extensively studied for exotic light manipulations via controlling the local-resonant modes in the microstructures. The coupling between these resonant modes has drawn growing interest in recent years due to the advanced functional metamaterial making the microstructures more and more complex. Here, the suppression of magnetic resonance of a dielectric cuboid, an analogue to the scattering cancellation effect or radiation control system, realized with an exterior cloaking in a hybrid metamaterial system, is demonstrated. Furthermore, the significant modulation of the absorption of the dielectric resonator in the hybrid metamaterial is also demonstrated. The physical insight of the experimental results is well illuminated with a classical double-harmonic-oscillator model, from which it is revealed that the complex coupling, i.e., the phase of coupling coefficient, plays a crucial role in the overall response of the metal-dielectric hybrid system. The proposed design strategy is anticipated to form a more straightforward and efficient paradigm for practical applications based on radiation control via versatile mode couplings.

Thermally controllable Mie resonances in a water-based metamaterial.

Active control of metamaterial properties is of great significance for designing miniaturized and versatile devices in practical engineering applications. Taking advantage of the highly temperature-dependent permittivity of water, we demonstrate a water-based metamaterial comprising water cubes with thermally tunable Mie resonances. The dynamic tunability of the water-based metamaterial was investigated via numerical simulations and experiments. A water cube exhibits both magnetic and electric response in the frequency range of interest. The magnetic response is primarily magnetic dipole resonance, while the electric response is a superposition of electric dipole resonance and a smooth Fabry-Pérot background. Using temporal coupled-mode theory (TCMT), the role of direct scattering is evaluated and the Mie resonance modes are analyzed. As the temperature of water cube varies from 20 °C to 80 °C, the magnetic and electric resonance frequencies exhibit obvious blue shifts of 0.10 and 0.14 GHz, respectively.

Realization of switchable EIT metamaterial by exploiting fluidity of liquid metal.

Novel manipulation techniques for the propagation of electromagnetic waves based on metamaterials can only be performed in narrow operating bands, and this drawback is a major challenge for developing metamaterial-based practical applications. We demonstrate that the scattering of metamaterials can be switched and that their operating band can be tuned by introducing liquid metal in the design of functional metamaterials. The proposed liquid metal-based metamaterial is composed of a copper wire pair and a tiny pipe filled with a liquid metal, namely eutectic gallium-indium. The interference of the sharp magnetic resonance of the copper wire pair and the broad dipolar mode of the liquid metal rod lead to an electromagnetically induced transparency (EIT)-like spectrum. We experimentally demonstrate that this EIT-like behavior can be switched on or off by exploiting the fluidity of the liquid metal, which is useful for multi-frequency modulators. These findings will hopefully promote the development of fluid matter-based metamaterials for extending the operating band of novel electromagnetic functions.

Facile synthesis of hierarchical chrysanthemum-like copper cobaltate-copper oxide composites for enhanced microwave absorption performance.

Hierarchical chrysanthemum-like CuCo2O4-CuO composites were successfully synthesized by a facile one-pot hydrothermal method after calcination at 500 °C. Based on the results of X-ray diffraction (XRD), Raman spectra, thermogravimetric analysis (TGA) and transmission electron microscope (TEM), we found that not only the morphology (from 2 dimensional to 3 dimensional) but also the crystalline structure (Cu0 + Cu2O + CoOx → CuO + CuCo2O4) of the samples could be tuned by the calcination temperature. The existed interfaces of CuCo2O4-CuCo2O4, CuCo2O4-CuO, and CuO-CuO played a key role on the attenuation of electromagnetic waves. The effective absorption frequency bandwidth is up to 4.02 GHz with a matched thickness of 2.8 mm. The CuCo2O4-CuO/paraffin composites can even exhibit bigger effective frequency bandwidth (from 4.02 to 4.65 GHz) if we turn the incident angle of electromagnetic (EM) wave to a proper value (i.e., 45°). We believe that the hierarchical chrysanthemum-like CuCo2O4-CuO composites can be a good candidate for the high-performance Co-based spinel microwave absorbers.

Controlling optical polarization conversion with Ge2Sb2Te5-based phase-change dielectric metamaterials.

Recent progress in the metamaterial-based polarization manipulation of light highlights the promise of novel polarization-dependent optical components and systems. To overcome the limited frequency bandwidth of metamaterials resulting from their resonant nature, it is desirable to incorporate tunability into metamaterial-based polarization manipulations. Here, we propose a dielectric metamaterial for controlling linear polarization conversion using the phase-change characteristic of Ge2Sb2Te5 (GST), whose refractive index changes significantly when transforming from the amorphous phase to the crystalline phase under external stimuli. The polarization conversion phenomena are systematically studied using different arrangements of GST in this metamaterial. The performance of linear polarization conversion and the tunability are also analyzed and compared in three different designs. It is found that phase-change materials such as GST can be employed in dielectric materials for tunable and switchable linear polarization conversion in the telecom band. The conversion efficiency can be significantly modulated during the phase transition. Our results provide useful insights for incorporating phase-change materials with metamaterials for tunable polarization manipulation.

High-Quality-Factor Mid-Infrared Toroidal Excitation in Folded 3D Metamaterials.

With unusual electromagnetic radiation properties and great application potentials, optical toroidal moments have received increasing interest in recent years. 3D metamaterials composed of split ring resonators with specific orientations in micro-/nanoscale are a perfect choice for toroidal moment realization in optical frequency considering the excellent magnetic confinement and quality factor, which, unfortunately, are currently beyond the reach of existing micro-/nanofabrication techniques. Here, a 3D toroidal metamaterial operating in mid-infrared region constructed by metal patterns and dielectric frameworks is designed, by which high-quality-factor toroidal resonance is observed experimentally. The toroidal dipole excitation is confirmed numerically and further demonstrated by phase analysis. Furthermore, the far-field radiation intensity of the excited toroidal dipoles can be adjusted to be predominant among other multipoles by just tuning the incident angle. The related processing method expands the capability of focused ion beam folding technologies greatly, especially in 3D metamaterial fabrication, showing great flexibility and nanoscale controllability on structure size, position, and orientation.

An electromagnetic modulator based on electrically controllable metamaterial analogue to electromagnetically induced transparency.

Electromagnetically induced transparency (EIT) is a promising technology for the enhancement of light-matter interactions, and recent demonstrations of the EIT analogue realized in artificial micro-structured medium have remarkably reduced the extreme requirement for experimental observation of EIT spectrum. In this paper, we propose to electrically control the EIT-like spectrum in a metamaterial as an electromagnetic modulator. A diode acting as a tunable resistor is loaded in the gap of paired wires to inductively tune the magnetic resonance, which induces remarkable modulation on the EIT-like spectrum through the metamaterial sample. The experimental measurements confirmed that the prediction of electromagnetic modulation in three narrow bands on the EIT-like spectrum, and a modulation contrast of up to 31 dB was achieved on the transmission through the metamaterial. Our results may facilitate the study on active/dynamical technology in translational metamaterials, which connect extraordinary manipulations on the flow of light in metamaterials, e.g., the exotic EIT, and practical applications in industry.