Atomic Transition Research Articles

Applied electric field to repair metal defects and accelerate dehydrogenation

Repairing metal micro-defects at the atomic level is very challenging due to their random dispersion and difficulty in identification. At the same time, the interaction of hydrogen with metal may cause hydrogen damage or embrittlement, endangering structural safety. As a result, it is critical to speed up the dehydrogenation of hydrogen-containing materials. The applied electric field can repair the vacancy defects of the material and accelerate the dehydrogenation of the hydrogen-containing metal. The influence of the external environment on the diffusion coefficient of hydrogen in polycrystalline metals was researched using molecular dynamics in this article, and the mechanism of hydrogen diffusion was investigated. Simultaneously, the mechanical characteristics of Fe3Cr alloy were compared during typical heat treatment and electrical treatment. The effect of temperature, electric field strength, and electric field direction on the diffusion coefficient was investigated using orthogonal test analysis. The results demonstrate that temperature and electric field strength have a significant impact on the diffusion coefficient. The atom vibrates violently as the temperature rises, breaking past the diffusion barrier and completing the atomic transition. The addition of the electric field adds extra free energy, decreases the atom’s activation energy, and ultimately enhances the atom’s diffusion coefficient. The repair impact of vacancy defects under electrical treatment is superior to that of typical annealing treatment for polycrystalline Fe3Cr alloy. The electric field can cause the dislocation to migrate, increasing the metal’s toughness and plasticity. This research serves as a useful reference for the electrical treatment of metal materials and offers a method for the quick dehydrogenation of hydrogen-containing materials.

Exploring the Potential of Residual Impurities in Germanium Detectors for MeV-Scale Dark Matter Detection

The direct detection of MeV-scale dark matter (DM) particles hinges on achieving an exceptionally low-energy detection threshold. Germanium (Ge) detectors, meticulously tailored with precise impurity compositions, hold the potential to enhance sensitivity to energy levels below the sub-electronvolt (sub-eV) range. This study explores the behavior of residual impurities inherent to Ge detectors at helium temperatures, unveiling a captivating freeze-out phenomenon leading to the formation of excited localized states known as dipole states. Using compelling evidence from relative capacitance measurements obtained from two detectors, we elucidate the transition of impurity atoms from free charge states to these dipole states as the temperature drops from 11 to 6.5 K. Our investigation comprehensively covers the intricate formation of these dipole states in both n-type and p-type impurities. Furthermore, we shed light on the electric field generated by these dipole states, revealing their ability to trap charges and facilitate the creation of cluster dipole states. Confirming findings from previous measurements, we establish that these excited dipole states exhibit a binding energy of less than 10 meV, offering an exceptionally low detection threshold for MeV-scale DM. Building upon this concept, we propose the development of a 1-kg Ge detector with internal charge amplification—an innovative approach poised to surpass electrical noise and enable the detection of MeV-scale DM with unprecedented sensitivity.

Measurement of steep dispersion associated with magnetically assisted gain in Zeeman degenerate two-level system of cold atoms

We report on the measurements of magnetically assisted dispersion and gain in a Zeeman degenerate two-level system associated with the closed D 2 hyperfine transition Fg=3→Fe=2 cold cesium atoms. We use a Mach–Zehnder interferometer to measure the dispersive properties of this system in the presence of a magnetic field, transversal to the quantization direction, when the atomic system is excited by a coupling and probe beams with orthogonal polarizations. We have measured the spectrum of the refraction index for different magnitudes of the external magnetic field and different coupling beam intensities. A previously published theoretical model, using a simpler atomic transition Fg=1→Fe=0 , accounts reasonably for the experimentally observed gain and dispersive lineshapes.

Precision spectroscopy of iodine absorption lines near the 1S0-3P2 transition of Yb atoms at 507 nm

We performed Doppler-free spectroscopy on the P(40)52-0 and P(52)53-0 lines of molecular iodine (127I2) near the 1S0-3P2 metastable transition of Yb at 507 nm. The frequency instability of an external-cavity diode laser locked to the observed hyperfine transitions of the 127I2 lines reached a level below 1.0 × 10−12, at the average time τ of the measurement of >10 s. The absolute frequency of the laser locked to the hyperfine transitions was measured with an uncertainty of 8 kHz (fractionally 1.4 × 10−11) using an optical frequency comb. The hyperfine transition intervals were fitted to a four-term Hamiltonian to validate the measurements and calculate the hyperfine constants of the iodine lines. The observed 30 hyperfine transitions of the P(40)52-0 and P(52)53-0 lines of 127I2 can be used as optical frequency references to investigate the 1S0-3P2 transition of Yb atoms.

The synergistic effect in the heteronuclear double-atom catalysts on CO activation: Insights from DFT calculations

In order to identify the synergistic effect in the heteronuclear double-atom catalysts (DACs) on CO activation, the homonuclear and heteronuclear DACs have been designed based on graphene supporter. And the three CO dissociation pathways have been considered using the density functional theory (DFT) calculation. It reveals that the heteronuclear DACs (MoX@NC) possesses higher catalytic ability than the homonuclear DACs (2X@NC) for CO activation. And the unpaired d-orbital electron plays a significant role on CO activation, which can change the magnetic moment of the DACs. The coordination atoms offer similar local coordination environment for the homonuclear and heteronuclear DACs. However, the Bader charge displays that there is a strong electronic interaction between Mo atom and other transition metals of dimer for the heteronuclear DACs. The synergistic effect of the heteronuclear DACs originates from the enhancement of the intermetallic interaction between the Mo atom and other transition metals. The work offers rational guideline for the synthesis of DACs with excellent catalytic performances, and has great potential for application in various catalytic fields.

VIP-2 with modulated current: pathfinder for enhanced Pauli exclusion principle violation studies

Fermions are subject to the Pauli Exclusion Principle (PEP), which is grounded on the spin-statistics theorem and, hence, related to the very same structure of the underlying symmetries. The VIP-2 (VIolation of Pauli exclusion principle - 2) experiment has been performing extreme sensitivity tests of the PEP, up to its current and final configuration, exploiting several experimental setups designed to study different theoretical models of PEP violation, looking for a faint signal of physics Beyond the Standard Model.A current is introduced in the copper target to bring new electrons into the system and, hence, fulfill the requirements of the Messiah-Greenberg Super-Selection rule. The searched spin-statistics violating signal corresponds to X-rays emitted when the new electrons perform atomic transitions to the already filled fundamental level of copper. This work analyzes the set of the VIP-2 data corresponding to a test run of 68 days in a current modulated regime alternating no current with current data-taking in short periods (50 s each), instead the usual alternating months-long data-taking of each of these two phases. We propose an analysis method to improve the experiment’s sensitivity: a spectral analysis constraint with the Discrete Fourier Transformation of the data. Compared to the spectrum-only analysis, about a factor of 1.5 of improvement to the limit for the probability of PEP violation for electrons was obtained.

Adiabatic elimination in the presence of multiphoton transitions in atoms inside a cavity

Various approaches have been used in the literature for eliminating nonresonant levels in atomic systems and deriving effective Hamiltonians. Important among these are elimination techniques at the level of probability amplitudes, operator techniques to project the dynamics on to the subspace of resonant levels, Green’s function techniques, the James’ effective Hamiltonian approach, etc. None of the previous approaches is suitable for deriving effective Hamiltonians in intracavity situations. However, the James’ approach does work in the case of only two-photon transitions in a cavity. A generalization of the James’ approach works in the case of three-photon transitions in a cavity, but only under Raman-like resonant conditions. Another important approach for adiabatic elimination is based on an adaptation of the Markov approximation well-known in the theory of system–bath interactions. However, this approach has not been shown to work in intracavity situations. In this paper, we present a method of adiabatic elimination for atoms inside cavities in the presence of multiphoton transitions. We work in the Heisenberg picture, and our approach has the advantage that it allows one to derive effective Hamiltonians even when Raman-like resonance conditions do not hold.

Atomic circulation in evanescent of LG 10 mode with active dipole and quadrupole transitions

The total internal reflection of a light with phase singularity, such as Laguerre–Gaussian (LG) light, can generate an evanescent wave. The distribution of this type of light is firmly localized in the vicinity above the dielectric surface and displays a rotational character. Any atom approaching the surface from the vacuum region interacts with evanescent wave and produces interesting rotational effects. Recent studies have established the coupling of LG beams to both electric atomic transitions; dipole and quadrupole according to the selection rules of each, permitted and prohibited. Due to the small magnitude of the quadrupole interaction compared to the dipole interaction, we chose the two counter-propagating beams configuration to generate the doubling Rabi frequencies with more stable surface optical forces. We describe the essential rotational features and discuss how they can be used to influence atoms. Atom confinement and dynamics in the interaction of surface optical vortices with the two different atomic transitions are illustrated using typical experimentally accessible parameters for the case of the Cs atom interacts with the L G 10 mode.

Numerical analysis of on-chip acousto-optic modulators for visible wavelengths.

On-chip acousto-optic modulators that operate at an optical wavelength of 780nm and a microwave frequency of 6.835GHz are proposed. The modulators are based on a lithium-niobate-on-sapphire platform and efficiently excite surface acoustic waves and exhibit strong interactions with tightly confined optical modes in waveguides. In particular, a high-efficiency phase modulator and single-sideband mode converter are designed. We found that for both microwave and optical wavelengths below 1µm, the interactions at the cross-sections of photonic waveguides are sensitive to the waveguide width and are significantly different from those in previous studies. Our designed devices have small footprints and high efficiencies, making them suitable for controlling rubidium atoms and realizing hybrid photonic-atomic chips. Furthermore, our devices have the potential to extend the acousto-optic modulators to other visible wavelengths for other atom transitions and for visible light applications, including imaging and sensing.

New diffraction-limited laser systems with variable output parameters operating in visible spectral range on copper atomic transitions for advanced material micromachining

New considerably improved laser systems (LS) featuring beam propagation factor equal to unit, two different laser pulse durations and an average output power from several tens of Watts up to 50 W are reported. Micron-sized machining is also demonstrated.

Lisbon Atomic Database (LISA): a compilation of calculated fundamental atomic parameters

The Lisbon Atomic Database (LISA) has a dedicated mission of compiling and providing a comprehensive collection of atomic parameters for the study of the interaction of X-rays with matter. This encompassing array of parameters spans a broad spectrum, extending from the calculation of electron impact ionization cross sections (EIICS) using the Modified Relativistic Binary Encounter Bethe model (MRBEB) , to pivotal data such as fluorescence and Coster–Kronig yields of atomic subshells, binding energies, and the full suite of radiative and non-radiative atomic transition parameters. Except for the EIICS values, all these parameters are obtained through ab initio calculations. These calculations are carried out using a self-consistent ab initio Multi-Configuration Dirac–Fock approach, supported by a specialized code developed by Desclaux, Indelicato, and others (MCDFGME).Graphical abstract

Melting-free integrated photonic memory with layered polymorphs

Abstract Chalcogenide-based nonvolatile phase change materials (PCMs) have a long history of usage, from bulk disk memory to all-optic neuromorphic computing circuits. Being able to perform uniform phase transitions over a subwavelength scale makes PCMs particularly suitable for photonic applications. For switching between nonvolatile states, the conventional chalcogenide phase change materials are brought to a melting temperature to break the covalent bonds. The cooling rate determines the final state. Reversible polymorphic layered materials provide an alternative atomic transition mechanism for low-energy electronic (small domain size) and photonic nonvolatile memories (which require a large effective tuning area). The small energy barrier of breaking van der Waals force facilitates low energy, fast-reset, and melting-free phase transitions, which reduces the chance of element segregation-associated device failure. The search for such material families starts with polymorphic In2Se3, which has two layered structures that are topologically similar and stable at room temperature. In this perspective, we first review the history of different memory schemes, compare the thermal dynamics of phase transitions in amorphous-crystalline and In2Se3, detail the device implementations for all-optical memory, and discuss the challenges and opportunities associated with polymorphic memory.

Eutectic structure induced by ordering of solute atoms leading to strengthening effects

In this study, Zr atoms transition from a disordered state to a short-range ordered state due to increased diffusion drive in high Zr content brazed joints. This atomic ordering leads to alternate nucleation of Ti2Ni/Ti2Cu and Zr2Ni/Zr2Cu primary phases along the same crystallographic direction, and the β-(Ti, Zr)2(Cu, Ni) eutectic structure with the <101> orientation is formed in the brazed joints. The growth of this eutectic structure absorbs the lattice distortion energy and reduces the number of low-angle grain boundaries. With the Zr content increased from 12 wt% to 37.5 wt%, low-angle grain boundaries can transfer to high-angle grain boundaries in the eutectic structure, enhancing the boundary misorientation about 53 %. The high misorientation hindered movable dislocations making them aggregated near the grain boundaries, which produce the eutectic structure strengthening effect. It increased to 726 MPa in the tensile strength of brazed joint with 20 wt% Zr content. This study has greatly improved our understanding of the intricate interactions between the ordering and strengthening of eutectic structures.

Observing dynamical phases of BCS superconductors in a cavity QED simulator.

In conventional Bardeen-Cooper-Schrieffer superconductors1, electrons with opposite momenta bind into Cooper pairs due to an attractive interaction mediated by phonons in the material. Although superconductivity naturally emerges at thermal equilibrium, it can also emerge out of equilibrium when the system parameters are abruptly changed2-8. The resulting out-of-equilibrium phases are predicted to occur in real materials and ultracold fermionic atoms, but not all have yetbeen directly observed. Here we realize an alternative way to generate the proposed dynamical phases using cavity quantum electrodynamics (QED). Our system encodes the presence or absence of a Cooper pair in a long-lived electronic transition in 88Sr atoms coupled to an optical cavity and represents interactions between electrons as photon-mediated interactions through the cavity9,10. To fully explore the phase diagram, we manipulate the ratio between the single-particle dispersion and the interactions after a quench and perform real-time tracking of the subsequent dynamics of the superconducting order parameter using nondestructive measurements. We observe regimes in which the order parameter decays to zero (phase I)3,4, assumes a non-equilibrium steady-state value (phase II)2,3 or exhibits persistent oscillations (phase III)2,3. This opens up exciting prospects for quantum simulation, including the potential to engineer unconventional superconductors and to probe beyond mean-field effects like the spectral form factor11,12, and for increasing the coherence time for quantum sensing.

Exploring the hydrogen atom: From wave function to stark effect

As the most basic and abundant atom in the universe, hydrogen atoms have long attracted the interest of scientists and provide the best subject for the exploration of quantum mechanics. This article provides a comprehensive study of the multifaceted characteristics and implications of the hydrogen atom. First, the research deeply studied the basic derivation of the Schrdinger equation of the hydrogen atom and provided the necessary theoretical framework. On this basis, modern computing tools are used to visualize the electron cloud of hydrogen atoms and reveal their shapes and characteristics under different orbits. In addition, the study investigated atomic transitions and associated spectra, elucidating basic quantum transition principles and serving as a benchmark for studying more complex atomic systems. Eventually, the research focus shifted to a specific direction, studying the Stark effect in hydrogen atoms, especially in the n=2 state. This research provides a novel perspective on understanding the fundamental properties of the hydrogen atom and its implications in modern physics research.

A strontium lattice clock with both stability and uncertainty below 5×10−18

We report the realization of the closed-loop operation of an optical lattice clock based on 87Sr atoms. A cavity-stabilized 698 nm laser is used to probe the 1S0→3P0 clock transition of strontium atoms trapped in optical lattices. Therein, we obtain a Fourier-limited Rabi spectrum with 0.6 Hz linewidth. The two transitions from mF=±9/2 ground states are alternatively interrogated to realize the closed-loop operation of the clock, and the clock laser light is frequency-stabilized to the center of the two transitions. Based on the interleaved measurement, the frequency instability of a single optical clock is optimized for the Dick effect, which is demonstrated to be 4.5×10−16/τ , with τ being the averaging time for measurement. Further, we build another similar setup of the strontium lattice clock, which is used for the asynchronous comparison between the two clocks, where the stability is measured as 2.1×10−18 at 47 000 s. Moreover, we carefully calibrate the systematic effects of the Sr1 optical clock, and the total uncertainty is evaluated as 4.4×10−18 .

Atomic level transition of graphene layer to carbon nanotubes over cobalt during ethanol decomposition reaction

Herein we report the catalytic ethanol decomposition over cobalt catalyst synthesized using conventional solution combustion synthesis (SCS). The reaction pathway proposed in-situ DRIFT analysis shows that the decomposition reaction proceeds through the formation of surface ethoxy intermediates that transformed into acetates and aldehydes which further decompose to releases CH4, H2 and CO2 with some deposition of carbon on the catalyst surface. The catalytic reaction shows 100 % ethanol conversion at 420 °C, with high selectivity of H2 in the output. The structural transformation of the catalyst and deposited carbon was analyzed using high-resolution transmission electron microscope (HRTEM). Presence of small Co nanoparticles (size <30 nm) surrounded with graphene and larger metal nanoparticles trapped inside MWCNTs was visible during a stability run over 50 h that motivates in proposing the reaction mechanism of the fluctuating metal nanoparticle along with carbon on the catalyst surface. Moreover, this work opens up the possibility of synthesizing highly dispersed Co nanoparticles in an efficient way without any complex experimental procedures and equipment that can further be used as effective catalysts in many industrial reactions.

Low-repetition-rate optical frequency comb

Reducing the pulse repetition rate of an optical frequency comb increases the pulse energy for a given average power. This enhances the efficiency of nonlinear frequency conversion and it facilitates extending the accessible wavelength range, for example, into the extreme ultraviolet (XUV). The resulting spectrally dense frequency comb can still be used for precision spectroscopy of narrow atomic or molecular transitions. In this paper, we demonstrate a low-noise infrared frequency comb with a repetition rate as low as 40 kHz using a Yb:KYW mode-locked laser, pulse picking, and subsequent amplification. The frequency comb structure is confirmed by generating a beat note with a continuous wave reference laser. A comb mode is actively stabilized to the reference laser, and the integrated rms phase noise from 20 Hz to 20 kHz is measured to be 195 mrad.

Electronic transitions and vibrational properties of bulk and monolayer g-C3N4, and a g-C3N4/MoS2 heterostructure from a DFT study.

Successful recognition of a dynamically stable carbonitride structure revealed that unlike other planar layered structures in the case of g-C3N4 the stable configurations are distorted [J. Wang et al., Chem. Mater., 2017, 29(7), 2694-2707, DOI: https://doi.org/10.1021/acs.chemmater.6b02969.]. This generates interest in a detailed study of the possibilities of controlling the structure and its properties both in its pristine and heterostructure forms. Here, we present the results of the investigation of dynamically stable bulk and monolayer g-C3N4, and a g-C3N4/MoS2 heterostructure. The bulk g-C3N4 was found to be an indirect band gap semiconductor exhibiting an indirect-to-direct band gap transition upon dimensionality reduction. In the case of the heterostructure, the analysis of partial density of states shows a charge transfer from nitrogen ions in g-C3N4 to the MoS2 layer. The Raman spectra of bulk g-C3N4 are discussed in detail, and the changes occurring in the spectra upon the transition to the monolayer form and in the g-C3N4/MoS2 heterostructure are demonstrated. It was found that the characteristic features of such an atomic transition can be seen in the region below 300 cm-1 and between 700 and 800 cm-1.

Tailoring two-photon spontaneous emission: Framework and nanoantenna design for interference and directionality

We develop a framework that computes two-photon spontaneous emission (TPSE) spectra of a quantum emitter near an arbitrarily shaped nanostructure. The model considers the interaction up to the electric quadrupolar order, which is relevant for nanophotonic structures sustaining strongly confined fields that are used to enhance and to tailor spontaneous emission processes. Moreover, we consider interference effects between multipolar two-photon emission channels, for the first time to our knowledge. First, we show for a s → s transition of a hydrogen atom placed under a silver plasmonic nanodisk a substantial enhancement in the photon-pair emission rates by 5 and 11 orders of magnitude for the two-electric dipole (2ED) and two-electric quadrupole (2EQ) transitions, respectively. Then for the same emitter under a plasmonic graphene nanotriangle, we demonstrate a breakdown of the electric dipole approximation in the TPSE process where the interference between the 2ED and 2EQ transitions is important, as it increases the total rate by 63 %. Third, we explore platforms where entangled photons of different energy are emitted in the far-field in different directions. In the end, our framework is a complete tool to design emitters and nanostructures for the TPSE process, leading to a rich assortment of functional nanoantennas.