Physica Scripta

Despite its amazing quantitative successes and contributions to revolutionary technologies, physics currently faces many unsolved mysteries ranging from the meaning of quantum mechanics to the nature of the dark energy that will determine the future of the Universe. It is clearly prohibitive for the general reader, and even the best informed physicists, to follow the vast number of technical papers published in the thousands of specialized journals. For this reason, we have asked the leading experts across many of the most important areas of physics to summarise their global assessment of some of the most important issues. In lieu of an extremely long abstract summarising the contents, we invite the reader to look at the section headings and their authors, and then to indulge in a feast of stimulating topics spanning the current frontiers of fundamental physics from 'The Future of Physics' by William D Phillips and 'What characterises topological effects in physics?' by Gerard 't Hooft through the contributions of the widest imaginable range of world leaders in their respective areas. This paper is presented as a preface to exciting developments by senior and young scientists in the years that lie ahead, and a complement to the less authoritative popular accounts by journalists.

The concept of the Fermi surface is at the very heart of our understanding of the metallic state. Displaying intricate and often complicated shapes, the Fermi surfaces of real metals are both aesthetically beautiful and subtly powerful. A range of examples is presented of the startling array of physical phenomena whose origin can be traced to the shape of the Fermi surface, together with experimental observations of the particular Fermi surface features.

First conceptualised in Olaf Stapledon's 1937 novel 'Star Maker', before being popularised by Freeman Dyson in the 1960s, Dyson Spheres are structures which surround a civilisation's sun to collect all the energy being radiated. This article presents a discussion of the features of such a feat of engineering, reviews the viability, scale and likely design of a Dyson structure, and analyses details about each stage of its construction and operation. It is found that a Dyson Swarm, a large array of individual satellites orbiting another celestial body, is the ideal design for such a structure as opposed to the solid sun-surrounding structure which is typically associated with the Dyson Sphere. In our solar system, such a structure based around Mars would be able to generate the Earth's 2019 global power consumption of 18.35 TW within fifty years once its construction has begun, which itself could start by 2040 using biennial launch windows. Alongside a 4.17 km² ground-based heliostat array, the swarm of over 5.5 billion satellites would be constructed on the surface of Mars before being launched by electromagnetic accelerators into a Martian orbit. Efficiency of the Dyson Swarm ranges from 0.74–2.77% of the Sun's 3.85 × 10²⁶ W output, with large potential for growth as both current technologies improve, and future concepts are brought to reality in the time before and during the swarm's construction. Not only would a Dyson Swarm provide a near-infinite, renewable power source for Earth, it would also allow for significant expansions in human space exploration and for our civilisation as a whole.

Many researchers have argued that humanity will create artificial general intelligence (AGI) within the next twenty to one hundred years. It has been suggested that AGI may inflict serious damage to human well-being on a global scale ('catastrophic risk'). After summarizing the arguments for why AGI may pose such a risk, we review the fieldʼs proposed responses to AGI risk. We consider societal proposals, proposals for external constraints on AGI behaviors and proposals for creating AGIs that are safe due to their internal design.

Squeezed light generation has come of age. Significant advances on squeezed light generation have been made over the last 30 years—from the initial, conceptual experiment in 1985 till today's top-tuned, application-oriented setups. Here we review the main experimental platforms for generating quadrature squeezed light that have been investigated in the last 30 years.

Let ${{ \mathcal O }}_{c}$ be the category of finite-length modules for the Virasoro Lie algebra at central charge c whose composition factors are irreducible quotients of reducible Verma modules. For any $c\in {\mathbb{C}}$, this category admits the vertex algebraic braided tensor category structure of Huang–Lepowsky–Zhang. Here, we begin the detailed study of ${{ \mathcal O }}_{{c}_{p,q}}$ where ${c}_{p,q}=1-\tfrac{6{\left(p-q\right)}^{2}}{{pq}}$ for relatively prime integers p, q ≥ 2; in conformal field theory, ${{ \mathcal O }}_{{c}_{p,q}}$ corresponds to a logarithmic extension of the central charge c_p,q Virasoro minimal model. We particularly focus on the Virasoro Kac modules ${{ \mathcal K }}_{r,s}$, $r,s\in {{\mathbb{Z}}}_{\geqslant 1}$, in ${{ \mathcal O }}_{{c}_{p,q}}$ defined by Morin-Duchesne–Rasmussen–Ridout, which are finitely-generated submodules of Feigin–Fuchs modules for the Virasoro algebra. We prove that ${{ \mathcal K }}_{r,s}$ is rigid and self-dual when 1 ≤ r ≤ p and 1 ≤ s ≤ q, but that not all ${{ \mathcal K }}_{r,s}$ are rigid when r > p or s > q. That is, ${{ \mathcal O }}_{{c}_{p,q}}$ is not a rigid tensor category. We also show that all Kac modules and all simple modules in ${{ \mathcal O }}_{{c}_{p,q}}$ are homomorphic images of repeated tensor products of ${{ \mathcal K }}_{\mathrm{1,2}}$ and ${{ \mathcal K }}_{\mathrm{2,1}}$, and we determine completely how ${{ \mathcal K }}_{\mathrm{1,2}}$ and ${{ \mathcal K }}_{\mathrm{2,1}}$ tensor with Kac modules and simple modules in ${{ \mathcal O }}_{{c}_{p,q}}$. In the process, we prove some fusion rule conjectures of Morin-Duchesne–Rasmussen–Ridout.

The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single- and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that nature cannot be local, that objective randomness exists and about the emergence of a classical world. It is suggestive that information plays a fundamental role also in the foundations of quantum physics.

The solar system started to form about 4.56 Gyr ago and despite the long intervening time span, there still exist several clues about its formation. The three major sources for this information are meteorites, the present solar system structure and the planet-forming systems around young stars. In this introduction we give an overview of the current understanding of the solar system formation from all these different research fields. This includes the question of the lifetime of the solar protoplanetary disc, the different stages of planet formation, their duration, and their relative importance. We consider whether meteorite evidence and observations of protoplanetary discs point in the same direction. This will tell us whether our solar system had a typical formation history or an exceptional one. There are also many indications that the solar system formed as part of a star cluster. Here we examine the types of cluster the Sun could have formed in, especially whether its stellar density was at any stage high enough to influence the properties of today's solar system. The likelihood of identifying siblings of the Sun is discussed. Finally, the possible dynamical evolution of the solar system since its formation and its future are considered.

In The Hitchhiker's Guide to the Galaxy, by Douglas Adams, the Answer to the Ultimate Question of Life, the Universe, and Everything is found to be 42—but the meaning of this is left open to interpretation. We take it to mean that there are 42 fundamental questions which must be answered on the road to full enlightenment, and we attempt a first draft (or personal selection) of these ultimate questions, on topics ranging from the cosmological constant and origin of the Universe to the origin of life and consciousness.

We review the concepts of temporal modes (TMs) in quantum optics, highlighting Roy Glauber's crucial and historic contributions to their development, and their growing importance in quantum information science. TMs are orthogonal sets of wave packets that can be used to represent a multimode light field. They are temporal counterparts to transverse spatial modes of light and play analogous roles—decomposing multimode light into the most natural basis for isolating statistically independent degrees of freedom. We discuss how TMs were developed to describe compactly various processes: superfluorescence, stimulated Raman scattering, spontaneous parametric down conversion, and spontaneous four-wave mixing. TMs can be manipulated, converted, demultiplexed, and detected using nonlinear optical processes such as three-wave mixing and quantum optical memories. As such, they play an increasingly important role in constructing quantum information networks.

Both the Jaynes-Cummings-Hubbard (JCH) and Dicke models can be thought of as idealised models of a quantum battery. In this paper we numerically investigate the charging properties of both of these models. The two models differ in how the two-level systems are contained in cavities. In the Dicke model, the N two-level systems are contained in a single cavity, while in the JCH model the two-level systems each have their own cavity and are able to pass photons between them. In each of these models we consider a scenario where the two-level systems start in the ground state and the coupling parameter between the photon and the two-level systems is quenched. Each of these models display a maximum charging power that scales with the size of the battery N and no super charging was found. Charging power also scales with the square root of the average number of photons per two-level system m for both models. Finally, in the JCH model, the power was found to charge inversely with the photon-cavity coupling κ.

Pantograph-OCS system sliding electrical contact is the only way for train energy transmission, which determines the safety and stability of energy transfer. And the current-carrying wear is the core factor that affecting the service performance of C-Cu contact pairs. C-Cu mate pairs often work for a long time in rainy/humid environments due to its exposed nature of work, and the contact interface often accumulates a large amount of water. Existing operating experience has shown that the carbon sliding plate of the pantograph experiences abnormal wear and frequent failure during rainfall, resulting in a significant decrease in service performance and lifespan. This article found that the thickness of the water film at the contact interface has a significant impact on the current carrying friction and wear performance of C-Cu contact pairs. When the thickness of the water film exceeds a certain range, the carbon skateboard will cause abnormal wear under high current, with the wear amount being more than three times the minimum value. The contact resistance also increases by 53.9%, which is related to the obstruction of current transmission. It also proves that the water film lubrication effect can be restored during the process of rainfall decreasing from large to small. The research can help to provide a suitable maintenance policy for pantograph and catenary system during the rainy season.

We investigate the silicon surface passivation property of Plasma Atomic Layer Deposited (PALD) hafnium oxide thin films and study its dependence on silicon (Si) doping type, film thickness, and post-deposition annealing conditions. Our results demonstrate that as-deposited HfO_x films exhibit poor passivation quality that can be improved by performing post-deposition annealing at 450 °C in hydrogen ambient. We demonstrate that the films can effectively passivate p-Si surfaces as compared to n-Si, where the surface passivation quality of the films improves with increasing film thickness for both silicon doping types. The best performance with a minority carrier lifetime of 1.7 ms, corresponding surface recombination velocity (SRV) ∼10 cm s⁻¹, is achieved for HfO_x films thickness ∼23 nm deposited on the p-Si substrate. The Capacitance-Voltage (C–V) measurements give an insight into the passivation mechanism of the studied films. Field effect passivation is found to be an important passivation mechanism in PALD-deposited HfO_x films, as revealed by C–V measurements. The films are also characterized using Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS), which reveals the chemical passivation provided by hydrogen ambient annealing. Overall, the impact of hafnium oxide film thickness and hydrogen ambient annealing conditions on silicon surface passivation is investigated. Our findings will help in utilizing plasma ALD process based HfO_x films for silicon solar cell device application.

This research describes the use of advanced simulation techniques to investigate use of different materials for a tube-in-tube heat exchanger. Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) simulations are employed to simulate thermal aspects and optimize the heat exchanger design. The objective is to identify the best-Suitable material combination considering both design and thermal considerations. The findings of this research contribute to the development of more efficient heat exchanger designs.

We have developed a graphical user interface (GUI) based package μ2mech to perform phase-field simulation for predicting microstructure evolution. The package can take inputs from ab initio calculations and CALPHAD (Calculation of Phase Diagrams) tools for quantitative microstructure prediction. The package also provides a seamless connection to transfer output from the mesoscale phase field method to the microscale finite element analysis for mechanical property prediction. Such a multiscale simulation package can facilitate microstructure-property correlation, one of the cornerstones in accelerated materials development within the integrated computational materials engineering (ICME) framework.

To achieve efficient solar cells, an in-depth review on significance of diffusion length enhancement is presented in this research work. We have focused on globally-adopted strategy of increasing diffusion length. The experimental pathways followed by various researchers to realize this strategy are deeply explored in this paper. The total of nine key-parameters that control and facilitate diffusion length enhancement are identified. Moreover, total of four parameters which are primarily influenced by diffusion length enhancement are listed. The underlying cause-&-effect mechanism pertaining to each parameter is discussed in-depth in this article. Furthermore, the comparison is performed between impact of electron and hole diffusion length enhancement on the device performance. The way to potentially implement this study for appropriate absorber layer selection is presented. Finally, a comparative study is performed on extent of influence of diffusion length enhancement technique to that of the band-offset optimization technique to achieve higher device performance. This rigorous analysis leads to discovery of the fact that diffusion length enhancement raises solar cell efficiency seven times as compared to that obtained by band offset optimization. Hence, significance of diffusion length enhancement for the pinnacle performance of solar cell is vividly revealed in this paper.

The development of advanced materials, new device architectures and fabrication processes will lead to more utilization of renewable energy sources like solar energy. Solar energy can be harvested more effectively using solar cells incorporated with advanced nanomaterials. Black phosphorus (BP) is a two-dimensional material in which the layers are stacked together through van der Waals forces. The electrical and optical properties of the material are much more suitable for use in solar cell applications. BP nanosheets have optoelectronic properties such as tunable bandgap (0.3 eV − 2.0 eV) and high carrier mobility that make them as suitable candidates for solar cells. Also, BP is able to absorb a wide range of light energy in the electromagnetic spectrum. Being a p-type semiconductor, BP finds applications in optoelectronic and semiconductor- devices. The optical absorption of the material is determined by its structural orientation. The material also possesses the high in-plane anisotropic band dispersion near the Fermi level in the Brillouin zone which results in a high direction-dependent optical and electronic properties. The major limitation of the material is its stability since it is degraded under the illumination of light. BP is used as an electron transport layer in solar cells similar to ZnO, TiO₂ and graphene. BP can also be integrated with hole transport layers and active materials. Research efforts have shown that BP and its derivatives have more potential to produce high efficiency solar cells. The application of BP in various solar cells and the enhancement in the efficiency of solar cells such as organic solar cells, perovskite solar cells, dye-sensitized solar cells and silicon solar cells are discussed in this review.

The laser powder bed fusion LPBF method in additive manufacturing for metals have proven to produce a final product with higher relative density, when compare to other metal additive manufacturing processes like WAAM, DED and it takes less time even for complex designs. Despite the use of many metal-based raw materials in the LPBF method for production of products. Maraging steel (martensitic steel) is used in aeronautical and aircraft applications in view of its advantages including low weight, high strength, long-term corrosion resistance, low cost, availability, and recyclability. A research gap concerns the selection of design, dimension, accuracy, process parameters according to different grades, and unawareness of various maraging steels other than specific maraging steels. In this comprehensive review, the research paper provides information about on LPBF maraging steel grades, their process parameters and defects, microstructure characteristics, heat treatments, and the resulting mechanical characteristics changes. In addition, detailed information about the aging properties, fatigue, residual and future scope of different maraging steel grades in LPBF for various applications are discussed.

The progress in IC miniaturization dictated by Moore's Law has taken a leap from mere circuit integration to IoT enabled System-on-Chip (SoC) deployments. Such systems are connoted by contemporary advancements in the semiconductor industry roadmaps namely, 'More-Moore' and 'More-than-Moore' (MtM). For meaningful integration of digital and non-digital blocks, a power performance tradeoff is essential for maximum and fruitful utilization of the silicon area. Using the techniques under the MtM nomenclature allows the use of unconventional steep slope devices like Tunneling FETs, Negative Capacitance (NC) FETs, Gate-all-around FETs (GAA) and FinFETs etc, which can exhibit reasonable performance with lower supply voltages. Following the Device Technology Co-optimization (DTCO) and System Technology Co-optimization (STCO) the advanced 3D heterogenous integration technologies allow sensors, analog/mixed signal and passive components to be assimilated within the same package as the CMOS blocks. Appropriate device engineering techniques like multi-gate architectures, vertical stacking transistors, compound semiconductors and alternate carrier transport phenomena are required to improve the current drive and scaling performance of advanced CMOS devices. CMOS based codesign is essential to realize new topologies for energy economical computation, sensing and information processing as the beyond CMOS steep slope devices are independently incapable of replacing conventional bulk CMOS devices. This article presents a detailed qualitative review of the various aspects of MtM beyond CMOS steep slope switches and their prospective integration technologies. For system level integration, various aspects of device performance and optimizations, related device-circuit interactions, dielectric technologies at the advance nanometer nodes have been probed into. Additionally, novel circuit topologies, synthesis algorithms and processor level performance evaluation using steep slope switches have been investigated. An exclusive compact overview for contemporary insights into integrated device-system development methodology and its performance evaluation is presented.

Designing of efficient thermoelectric material is the need of hour to avoid the adverse effect on environment. Two-dimensional (2D) transition metal oxides (TMOs) and transition metal dichalogenides (TMDCs) are receiving attention of researchers due to their wide range of electronic properties, high temperature and air stability, tunable electron transport properties for high thermoelectric efficiency (ZT). Two- dimensionalization in these materials lead to the increase in their thermoelectric efficiency as compared to their bulk counterpart due to the quantum confinement effect. These materials possess high thermoelectric efficiency even at high temperature (500–800 K) but their application still lagging behind commercially due to low ZT value. Various approaches such as strain engineering, defect engineering etc. Were adopted to further enhance the ZT value of these materials. Controlling chalcogen atomic defect provides an alternative avenue for engineering a wide range of physical and chemical properties of 2D TMOs/TMDCs. In this review we will systematically present the progress made in the study of electronic, phononic, transport properties and Seebeck coefficient of 2D TMOs/TMDCs such as XO₂ (X=Cr, Mo, Zr) and MX₂ (M= Cr, Mo, Zr; X= S, Se, Te) by using first principle approach. Methodologies such as strain engineering and doping to enhance the ZT values has also been discussed. In the last section we have discussed the experimental results of thermoelectric parameters of TMDCs and compare them with the existing theoretical results. It is concluded from this study that there are plenty of rooms which can be explored both theoretically and experimentally to design efficient thermoelectric materials for energy harvesting.

Both the Jaynes-Cummings-Hubbard (JCH) and Dicke models can be thought of as idealised models of a quantum battery. In this paper we numerically investigate the charging properties of both of these models. The two models differ in how the two-level systems are contained in cavities. In the Dicke model, the N two-level systems are contained in a single cavity, while in the JCH model the two-level systems each have their own cavity and are able to pass photons between them. In each of these models we consider a scenario where the two-level systems start in the ground state and the coupling parameter between the photon and the two-level systems is quenched. Each of these models display a maximum charging power that scales with the size of the battery N and no super charging was found. Charging power also scales with the square root of the average number of photons per two-level system m for both models. Finally, in the JCH model, the power was found to charge inversely with the photon-cavity coupling κ.

An analytical expression for the intensity distribution of a focused continuous Hermite-Gaussian beam after passing through a positive lens has been derived. Analytically, this intensity has been used to derive the gradient force acting on a nano-dielectric particle sphere. It is found that, the beam modes (p, l) have a direct influence on the trap stability, the number of trapping regions, the area of trapping zones and the particle size range.

The inverted pendulum is a mechanical system with a rapidly oscillating pivot point. Using techniques similar in spirit to the methodology of effective field theories, we derive an effective Lagrangian that allows for the systematic computation of corrections to the so-called Kapitza equation. The derivation of the effective potential of the system requires non-trivial matching conditions, which need to be determined order by order in the power-counting of the problem. The convergence behavior of the series is investigated on the basis of high-order results obtained by this method.

Prolate to oblate shape transitions have been predicted in an analytic way in the framework of the Interacting Boson Model (IBM), determining O(6) as the symmetry at the critical point. Parameter-independent predictions for prolate to oblate transitions in various regions on the nuclear chart have been made in the framework of the proxy-SU(3) and pseudo-SU(3) symmetries, corroborated by recent non-relativistic and relativistic mean field calculations along series of nuclear isotopes, with parameters fixed throughout, as well as by shell model calculations taking advantage of the quasi-SU(3) symmetry. Experimental evidence for regions of prolate to oblate shape transitions is in agreement with regions in which nuclei bearing the O(6) dynamical symmetry of the IBM have been identified, lying below major shell closures. In addition, gradual oblate to prolate transitions are seen when crossing major nuclear shell closures, in analogy to experimental observations in alkali clusters.

Terawatt x-ray free-electron lasers (XFELs) represent the frontier in further development of x-ray sources and require high current densities with strong transverse focusing. In this paper, we investigate the implications/potentialities of TW XFELs on the generation of harmonics at still shorter wavelengths and higher photon energies. The simulations indicate that significant power levels are possible at high harmonics of the XFEL resonance and that these XFELs can be an important coherent source of hard x-rays through the gamma ray spectrum. For this purpose, we use the MINERVA simulation code which self-consistently includes harmonic generation. Both helical and planar undulators are discussed in which the fundamental is at 1.5 Å and study the associated harmonic generation. While tapered undulators are needed to reach TW powers at the fundamental, the taper does not enhance the harmonics because the taper must start before saturation of the fundamental, while the harmonics saturate before this point is reached. Nevertheless, the harmonics reach substantial powers. Simulations indicate that, for the parameters under consideration, peak powers of the order of 180 MW are possible at the fifth harmonic with a photon energy of about 41 keV and still high harmonics may also be generated at substantial powers. Such high harmonic powers are certain to enable a host of enhanced applications.

For an undirected connected graph G = G(V, E) with vertex set V(G) and edge set E(G), a subset R of V is said to be a resolving in G, if each pair of vertices (say a and b; a ≠ b) in G satisfy the relation d(a, k) ≠ d(b, k), for at least one member k in R. The minimum set R with this resolving property is said to be a metric basis for G, and the cardinality of such set R, is referred to as the metric dimension of G, denoted by dim_v(G). In this manuscript, we consider a complex molecular graph of one-heptagonal carbon nanocone (represented by HCN_s) and investigate its metric basis as well as metric dimension. We prove that just three specifically chosen vertices are enough to resolve the molecular graph of HCN_s. Moreover, several theoretical as well as applicative properties including comparison have also been incorporated.

Nonlinear absorption properties of PbMo_0.75W_0.25O₄ single crystal fabricated by the Czochralski method were studied. The band gap energy of the crystal was determined as 3.12 eV. Urbach energy which represents the defect states inside the band gap was found to be 0.106 eV. PbMo_0.75W_0.25O₄ single crystal has a broad photoluminescence emission band between 376 and 700 nm, with the highest emission intensity occurring at 486 nm and the lowest intensity peak at 547 nm, depending on the defect states. Femtosecond transient absorption measurements reveal that the lifetime of localized defect states is found to be higher than the 4 ns pulse duration. Open aperture (OA) Z-scan results demonstrate that the PbMo_0.75W_0.25O₄ single crystal exhibits nonlinear absorption (NA) that includes two-photon absorption (TPA) as the dominant mechanism at the 532 nm excitations corresponding to 2.32 eV energy. NA coefficient (β_eff) increased from 7.24 × 10⁻¹⁰ m W⁻¹ to 8.81 × 10⁻¹⁰ m W⁻¹ with increasing pump intensity. At higher intensities β_eff tends to decrease with intensity increase. This decrease is an indication that saturable absorption (SA) occurred along with the TPA, called saturation of TPA. The lifetime of the defect states was measured by femtosecond transient absorption spectroscopy. Saturable absorption behavior was observed due to the long lifetime of the localized defect states. Closed aperture (CA) Z-scan trace shows the sign of a nonlinear refractive index. The optical limiting threshold of PbMo_0.75W_0.25O₄ single crystal at the lowest intensity was determined as 3.45 mJ/cm². Results show that the PbMo_0.75W_0.25O₄ single crystal can be a suitable semiconductor material for optical limiting applications in the visible region.

To improve predictive machine learning-based models limited by sparse data, supplemental physics-related features are introduced into a deep neural network (DNN). While some approaches inject physics through differential equations or numerical simulation, improvements are possible using simplified relationships from engineering references. To evaluate this hypothesis, thin rectangular plates were simulated to generate training datasets. With plate dimensions and material properties as input features and fundamental natural frequency as the output, predictive performance of a data-driven DNN-based model is compared with models using supplemental inputs, such as modulus of rigidity. To evaluate model accuracy improvements, these additional features are injected into various DNN layers, and the network is trained with four different dataset sizes. When evaluated against independent data of similar features to the training sets, supplementation provides no statistically-significant prediction error reduction. However, notable accuracy gains occur when independent test data is of material and dimensions different from the original training set. Furthermore, when physics-enhanced data is injected into multiple DNN layers, reductions in mean error from 33.2% to 19.6%, 34.9% to 19.9%, 35.8% to 22.4%, and 43.0% to 28.4% are achieved for dataset sizes of 261, 117, 60, and 30, respectively, demonstrating potential for generalizability using a data supplementation approach. Additionally, when compared with other methods—such as linear regression and support vector machine (SVM) approaches—the physics-enhanced DNN demonstrates an order of magnitude reduction in percentage error for dataset sizes of 261, 117, and 60 and a 30% reduction for a size of 30 when compared with a cubic SVM model independently tested with data divergent from the training and validation set.

The main challenge of quantum computing on its way to scalability is the erroneous behaviour of current devices. Understanding and predicting their impact on computations is essential to counteract these errors with methods such as quantum error mitigation. Thus, it is necessary to construct and evaluate accurate noise models. However, the evaluation of noise models does not yet follow a systematic approach, making it nearly impossible to estimate the accuracy of a model for a given application. Therefore, we developed and present a systematic approach to benchmarking noise models for quantum computing applications. It compares the results of hardware experiments to predictions of noise models for a representative set of quantum circuits.
We also construct a noise model containing five types of quantum noise and optimize its parameters using a series of training circuits. We compare its accuracy to other noise models by volumetric benchmarks involving typical variational quantum circuits. The model can easily be expanded by adding new quantum channels.

Creating a massive spatial quantum superposition, such as the Schrödinger cat state, where the mass and the superposition size within the range 10⁻¹⁹ − 10⁻¹⁴ kg and Δx ∼ 10 nm − 100 μm, is a challenging task. The methods employed so far rely either on wavepacket expansion or on a quantum ancilla, e.g. single spin dependent forces, which scale inversely with mass. In this paper, we present a novel approach that combines gravitational acceleration and diamagnetic repulsion to generate a large spatial superposition in a relatively short time. After first creating a modest initial spatial superposition of 1 μm, achieved through techniques such as the Stern–Gerlach (SG) apparatus, we will show that we can achieve an ∼10²−10³ fold improvement to the spatial superposition size (1 μm → 980 μm) between the wave packets in less than 0.02 s by using the Earth's gravitational acceleration and then the diamagnetic repulsive scattering of the nanocrystal, neither of which depend on the object mass. Finally, the wave packet trajectories can be closed so that spatial interference fringes can be observed. Our findings highlight the potential of combining gravitational acceleration and diamagnetic repulsion to create and manipulate large spatial superpositions, offering new insights into creating macroscopic quantum superpositions.