Two-dimensional Atom Research Articles

Coulomb impurities in graphene driven by fast ions

Abstract We provide a theoretical model for electronic transitions in a two-dimensional (2D) artificial atom in a graphene monolayer. The artificial atom is due to the presence of a charged adatom (Coulomb impurity) in the layer and interacts with a fast ultrarelativistic ion moving parallel to the layer. We compute the probability and cross sections for the corresponding electronic transitions by means of an exact solution of the time-dependent 2D Dirac equation describing the interaction of the planar atom with the electromagnetic field of the ultrarelativistic projectile.

Superposition of standing waves induced ultra high-resolution atom localization

Abstract In this study, we have theoretically demonstrated ultra-high resolution two-dimensional atom localization within a three-level $\lambda$-type atomic medium via superposition of asymmetric and symmetric standing wave fields. Our analysis provides understanding into the precise spatial localization of atomic positions at the atomic level, utilizing advanced theoretical approaches and principles of quantum mechanics. The dynamical behavior of a three-level atomic system is thoroughly analyzed using the density matrix formalism within the realm of quantum mechanics. A theoretical approach is constructed to describe the interaction between the system and external fields, specifically a control field and a probe field. The absorption spectrum of the probe field is thoroughly examined to clarify the spatial
localization of the atom within the proposed configuration. We have theoretically investigated that symmetric and asymmetric superposition phenomena significantly influence the localized peaks within a two-dimensional spatial domain. Specifically, the emergence of one and two sharp localized peaks has been observed within a region of one wavelength domain. We observed notable influences of the intensity of the control field, probe field detuning, and decay rates on atom localization. Ultimately, we have achieved an unprecedented level of ultra-high resolution and precision in localizing an atom within an area smaller than λ/35×λ/35. These findings hold promise for potential applications in domains such as Bose-Einstein condensation, nanolithography, laser cooling, trapping of neutral atoms, and the measurement of center-of-mass wave-functions.

Amorphous quantum magnets in a two-dimensional Rydberg atom array

Amorphous quantum magnets in a two-dimensional Rydberg atom array

Coulomb impurities in graphene driven by ultrashort electromagnetic pulses: excitation, ionization, and pair creation

We provide a theory for electronic transitions induced by ultrashort electromagnetic pulses in two-dimensional artificial relativistic atoms which are created by a charged impurity in a gapped graphene monolayer. Using a non-perturbative sudden-perturbation approximation, we derive and discuss analytical expressions for the probabilities for excitation, ionization and electron-hole pair creation in this system.

High-precision two- and three- dimensional atom localization in a microwave and radio-frequency driven Δ∇ system

We introduce a new approach for precise and high-resolution two-dimensional (2D) and three-dimensional (3D) atom localization in a four-level Δ∇ atomic system driven by microwave (M) and radio frequency (R) fields. In the proposed work, additional microwave and radio-frequency fields are utilized for an efficient control of the localization precision. Due to the spatially varying atom-field interaction, the probe susceptibility become position dependent and therefore, one can directly ascertain the position probability distribution of an atom by analyzing the probe spectra. The phase-sensitive property of the atomic system plays a significant role in substantially reducing the uncertainty associated with atom position measurements. We have studied the system behavior through the analysis of dressed states, which forms the basis for its physical interpretation. The increase in precision for measuring the atom’s position is a result of interference between one-photon excitation and the phase-dependent three-photon excitation arising from the closed interacting contour within the laser-driven atomic system, as demonstrated through both numerical calculations and qualitative analyses. The findings indicate that precise sub-wavelength atom localization can be attained by appropriately adjusting the system parameters. Also, the optimal adjustment of these parameters can lead to 100% probability of locating the atom at a particular position within 2D and 3D subspaces.

Microwave-controlled two-dimensional atom localization in a five-level Rydberg atom-laser interaction system and its application as a phase-diffraction cross-grating

Microwave-controlled two-dimensional atom localization in a five-level Rydberg atom-laser interaction system and its application as a phase-diffraction cross-grating

Variational Monte Carlo with large patched transformers

Large language models, like transformers, have recently demonstrated immense powers in text and image generation. This success is driven by the ability to capture long-range correlations between elements in a sequence. The same feature makes the transformer a powerful wavefunction ansatz that addresses the challenge of describing correlations in simulations of qubit systems. Here we consider two-dimensional Rydberg atom arrays to demonstrate that transformers reach higher accuracies than conventional recurrent neural networks for variational ground state searches. We further introduce large, patched transformer models, which consider a sequence of large atom patches, and show that this architecture significantly accelerates the simulations. The proposed architectures reconstruct ground states with accuracies beyond state-of-the-art quantum Monte Carlo methods, allowing for the study of large Rydberg systems in different phases of matter and at phase transitions. Our high-accuracy ground state representations at reasonable computational costs promise new insights into general large-scale quantum many-body systems.

Spatial entanglement in two-dimensional artificial atoms

Semiconductor quantum dots (QDs) are one of the leading candidates for realizable qubits, as well as for many other advances in quantum computing and quantum communication. The spatial overlapping of wavefunctions describing each single electron in these nanoscale devices results in tunable spatial entanglement. In this article, we explore the case of two electrons in two-dimensional double quantum dot systems. We compute the two-particle wavefunction through a variational method combined with Hermite finite elements and study the spatial entanglement of electrons. We show that symmetry in the geometry of the double quantum dots plays a role in obtaining optimal entanglement, while a broken symmetry can lead to additional resonances in entanglement that are associated with the crossings of states. We also show that one can finely tune the level of spatial entanglement by altering the geometry of the quantum dots or by applying external fields, which corresponds to an “entanglement spectroscopy.” Finally, we study how impurities in the potential profile of the QDs affect the level of entanglement.

Randomized Benchmarking Using Nondestructive Readout in a Two-Dimensional Atom Array.

Neutral atoms are a promising platform for scalable quantum computing, however, prior demonstration of high fidelity gates or low-loss readout methods have employed restricted numbers of qubits. Using randomized benchmarking of microwave-driven single-qubit gates, we demonstrate average gate errors of 7(2)×10^{-5} on a 225 site atom array using conventional, destructive readout. We further demonstrate a factor of 1.7 suppression of the primary measurement errors via low-loss, nondestructive, and state-selective readout on 49 sites while achieving gate errors of 2(9)×10^{-4}.

An Overview of Recycling Wastes into Graphene Derivatives Using Microwave Synthesis; Trends and Prospects.

It is no secret that graphene, a two-dimensional single-layered carbon atom crystal lattice, has drawn tremendous attention due to its distinct electronic, surface, mechanical, and optoelectronic properties. Graphene also has opened up new possibilities for future systems and devices due to its distinct structure and characteristics which has increased its demand in a variety of applications. However, scaling up graphene production is still a difficult, daunting, and challenging task. Although there is a vast body of literature reported on the synthesis of graphene through conventional and eco-friendly methods, viable processes for mass graphene production are still lacking. This review focuses on the variety of unwanted waste materials, such as biowastes, coal, and industrial wastes, for producing graphene and its potential derivatives. Among the synthetic routes, the main emphasis relies on microwave-assisted production of graphene derivatives. In addition, a detailed analysis of the characterization of graphene-based materials is presented. This paper also highlights the current advances and applications through the recycling of waste-derived graphene materials using microwave-assisted technology. In the end, it would alleviate the current challenges and forecast the specific direction of waste-derived graphene future prospects and developments.

Exploring the experimental study and density functional theory calculations of symmetric and asymmetric chalcogen atoms interacted molybdenum dichalcogenides for lithium-ion batteries

Two-dimensional asymmetric chalcogen atoms attached to Janus nanoparticles have fascinated research attention owing to their distinctive properties and characteristics for various applications. This paper proposed a facile synthesis to produce efficient molybdenum-based symmetric and asymmetric chalcogens bounded by XMoX and TeMoX nanostructures. Subsequently, the fabricated XMoX and TeMoX nanostructures were employed as anodes for lithium-ion batteries (LIBs). Assembled LIBs using TeMoS and TeMoSe Janus anodes achieved 2610 and 2073 mAh g–1 reversible capacity at 0.1 A g–1, respectively for the half-cell configuration, which is outstanding performance compared with previous reports. Superior rate capability performances at 0.1–20 A g–1 and exceptional cycling solidity confirmed high charge and discharge capacities for TeMoX Janus lithium-ion battery anodes. In addition, the full cell device with TeMoS//LiCoO2 configuration explored the discharge capacity of 1605 mAh g−1 at 0.1 A g–1 which suggests their excellent electrochemical characteristics. The density functional theory approximations established the significance of assembled symmetric and asymmetric chalcogen atoms interacted with XMoX and TeMoX anode materials for LIBs. Thus, the present investigation supports a new approach to creating two-dimensional materials based on asymmetric chalcogen atoms with core metal to effectively increase desirable energy storage characteristics.

Effects of Electric Field and External Magnetic Field on the Electronic and Thermoelectric Properties of the h-BAs Monolayer and Bilayer: Tight-Binding Approach

Newly, two-dimensional (2D) materials atoms of groups IV and III-V have obtained extensive attention due to their novel properties. In this work, we apply the tight-binding model and Green’s function approach to the hexagonal boron arsenide (h-BAs) monolayer and bilayer to investigate their electronic and thermoelectric properties. We find that the h-BAs monolayer behaves as a p-type semiconductor and it can be changed to the n-type by applying the external magnetic field. Also, the h-BAs bilayer with (A-A) stacked has a semi-metallic property but (A-B) stacked is a semiconductor. The results show that the band gap can be controlled by applying an electric field and an external magnetic field. We obtain that the thermal and electrical conductivity of the h-BAs monolayer and bilayer increase in the presence of an electric field and an external magnetic field. More, controlling the Seebeck coefficient of the material is a unique phenomenon that provides advanced applications for these materials in thermoelectric coolers and waste heat harvesting. Here, we have been able to regulate the Seebeck coefficient of the h-BAs monolayer and bilayer by using the electric and external magnetic fields.

Quantum phase transition of a two-dimensional Rydberg atom array in an optical cavity

We study the two-dimensional Rydberg atom array in an optical cavity with help of the meanfield theory and the large-scale quantum Monte Carlo simulations. The strong dipole-dipole interactions between Rydberg atoms can make the system exhibit the crystal structure, and the coupling between two-level atom and cavity photon mode can result in the formation of the polariton. The interplay between them provides a rich quantum phase diagram including the Mott, solid-1/2, superradiant and superradiant solid phases. As the two-order co-existed phase, the superradiant solid phase breaks both translational and U(1) symmetries. Based on both numerical and analytic results, we found the region of superradiant solid is much larger than one dimensional case, so that it can be more easily observed in the experiment. Finally, we discuss how the energy gap of the Rydberg atom can affect the type of the quantum phase transition and the number of triple points.

A Comprehensive Review on Graphene Nanoparticles: Preparation, Properties, and Applications

Graphene, with its amazing prospects and nonpareil aspects, has enticed scientists and researchers all over the globe in a significant fashion. Graphene, the super material, endlessly demonstrates some of the substantial, as well as desired, mechanical, thermal, optical, and chemical characteristics which are just about to bring about an unprecedented transformation in the science and technology field. Being derived from graphite, graphene is made of one-atom-thick, two-dimensional carbon atoms arranged in a honeycomb lattice. This Nobel-prize-winning phenomenon includes properties that may result in a new dawn of technology. Graphene, the European Union’s (EU) largest pledged project, has been extensively researched since its discovery. Several stable procedures have been developed to produce graphene nanoparticles in laboratories worldwide. Consequently, miscellaneous applications and futuristic approaches in artificial intelligence (AI)-based technology, biomedical and nanomedicine, defence and tactics, desalination, and sports are ruling over the next generation’s fast-paced world and are making the existing market competitive and transformative. This review sheds light upon the ideology of the preparation and versatile application of graphene and foretells the upcoming advancements of graphene nanoparticles with the challenges rearing ahead. The study also considers graphene nanoparticles’ diverse fields and portends their sustainability with the possibility of their acceptance in the commercial market as well as in common usage.

Two-dimensional atom localization and formation of waveguide channels using Bragg diffraction law

Atoms of four-level atomic medium are doped in a crystal slab of silica which is immersed in a four-level atomic medium. We incorporated Bragg law in the Rabi frequencies of the driving fields and obtained absorption spectrum which exhibits atom localization inside the crystal plane and generation of waveguide channels. Varying the Bragg angle θ, leads to a number of localized peaks and craters. The number of peaks decreases as we increase the Bragg angle θ from π/8 to π/2 and the peaks disappear beyond this angle. The localization probability is independent of the Bragg angle, while the spatial resolution varies with change in Bragg angle. However, the probe detuning and amplitudes of Rabi frequencies change the localization probability. Inside the optical lattice of the silica crystal, waveguide channels and particle traps are generated which may be utilized to guide electromagnetic radiations and trap quantum particles. This work is useful for coherent control information of crystal planes, optical trapping, waveguide channels of nano crystals and data storage.

Ultraprecise Off-Axis Atom Localization With Hybrid Fields

Atom localization enables a high-precision imaging of the atomic position, which has provided vast applications in fundamental and applied science. In the present work, we propose a scheme for realizing two-dimensional off-axis atom localization in a three-level Λ system. Benefiting from the use of a hybrid coupling field, which consists of one Gaussian beam and one Laguerre–Gaussian beam, our scheme shows that the atoms can be localized at arbitrary position with high spatial resolution. Considering realistic experimental parameters, our numerical simulation predicts that the atoms can be precisely localized with a spatial resolution of ∼200 nm in the range of a radial distance of a few micrometers to the beam core. Our results provide a more flexible way to localize atoms in a two-dimensional system, possibly paving one-step closer to the nanometer scale atom lithography and ultraprecise microscopy.

Raman Spectroscopy Investigation on Semi-curve Woven Fabric-graphene Synthesized by the Chemical Vapor Deposition Process

Abstract: Graphene is a single layer of two-dimensional carbon atoms bound in a hexagonal lattice structure with zero band gap semiconductor. Chemical vapor deposition (CVD) is one of the most promising, inexpensive and readily ways for synthesizing monolayer pristine graphene. We have synthesized monolayer graphene shaped in semi-curve woven frabic-graphene (SWF-G) on SiO2/Si substrate. Using Raman spectroscopy, we studied the central suspended portion (i.e., 1-6) of it exerting compression (stress) to the graphene supported on the substrate. The concentration of hole impurities on either side of the central position of semi-curve woven fabric-graphene (SWF-G) is more than on its central position. The variation of such hole doping concentration results in an upshift of 2D peak position (pos(2D)) which is opposite for high electron doping even if there is no intentional control of doping. The synthesized graphene is a single-layer high-quality new structure graphene. Keywords: Semi-curve woven fabric-graphene, Raman spectroscopy, Charge impurities, Compression, Doping.

Molecular Free Electron Vortices in Photoionization by Polarization-Tailored Ultrashort Laser Pulses.

Atomic and molecular free electron vortices (FEVs), characterized by their spiral-shaped momentum distribution, have recently attracted a great deal of attention due to their varied shapes and their unusual topological properties. Shortly after their theoretical prediction by the single-photon ionization (SPI) of He atoms using pairs of counterrotating circularly polarized attosecond pulses, FEVs have been demonstrated experimentally by the multiphoton ionization (MPI) of alkali atoms using single-color and bichromatic circularly polarized femtosecond pulse sequences. Recently, we reported on the analysis of the experimental results employing a numerical model based on the ab initio solution of the time-dependent Schrödinger equation (TDSE) for a two-dimensional (2D) atom interacting with a polarization-shaped ultrashort laser field. Here, we apply the 2D TDSE model to study molecular FEVs created by SPI and MPI of a diatomic molecule using polarization-tailored single-color and bichromatic femtosecond pulse sequences. We investigate the influence of the coupled electron-nuclear dynamics on the vortex formation dynamics and discuss the effect of CEP- and rotational averaging on the photoelectron momentum distribution. By analyzing how the molecular structure and dynamics is imprinted in the photoelectron spirals, we explore the potential of molecular FEVs for ultrafast spectroscopy.

Reflection, transmission, and surface susceptibility tensor of two-dimensional materials

In a recent experiment, the out-of-plane surface susceptibility of a single-layer two-dimensional atom crystal in the visible spectrum has been measured. This susceptibility gives a measurable contribution to the reflectivity of two-dimensional materials. Here we provide a complete theoretical description of the reflective properties, considering incoming s and p polarized plane waves at any angle of incidence on the crystal, computing local, reflected and transmitted electromagnetic fields. We finally connect the microscopic polarizability to both the in-plane and the out-of-plane macroscopic surface susceptibilities.

Polarons and bipolarons in two-dimensional systems

Polarons and bipolarons in two-dimensional (2 D) crystals with a simple conduction band are considered in the work. A study of the potential of pair interaction for the singlet states of polarons was carried out in the region intermediate coupling. The effective functional of exchange-coupled pair of polarons was obtained by the Buimistrov-Pekar method. Variational calculations of the singlet states energies were carried out taking into account the direct dependence of the wave function of the system on the interelectron distance. The variational functions have been selected in the form of a multiparameter system of Gaussian functions with exponentially correlated multipliers. The region of existence of a two-dimensional bipolaron was determined as a function of the crystal parameters. It has been shown that a single-center configuration (a configuration similar to a two-dimensional helium atom) is stable. The minimum corresponding to the two-center configuration (“polaron molecule”) is secondary extremum that disappears when the electronic correlations associated with the direct dependence of the wave function of the system on the distance between electrons are taken into account. The main energy minimum corresponds to single-center configuration. The study of the fulfillment of the virial theorem for polaron and bipolaron functionals was carried out. The results of variational calculations were compared with the calculations performed by other authors. Two-center configuration of a 2D bipolaron is unstable. The only minimum corresponds to a one-center 2D bipolaron. Exchange energy of two 2D polarons is antiferromagnetic.