Trapping Of Atoms Research Articles

Fabrication of nitrogen-doped carbon on NiCoP electrocatalyst with flower-like structure for efficient hydrogen evolution reaction in alkaline solution

The development of hydrogen evolution catalysts with low cost, high activity, and outstanding stability has become an urgent need. Herein, we reported a novel and effective strategy for the in situ growth of NiCoP nanoparticles encapsulated in ultrathin nitrogen-doped porous carbon on nickel foam (NiCoP@NC/NF). Compared with NiCoP/NF, the NiCoP@NC/NF presented a much larger electrochemically active surface area (ECSA) (1402.9 cm2 mg−1), more abundant intrinsic HER active sites and lower charge-transfer resistance, leading to superior catalytic activity. The as-prepared NiCoP@NC/NF electrode exhibited extremely low overpotential η10 (77 mV) and Tafel slope (62.1 mV dec−1) for HER in 1.0 M KOH as the electrolyte. Importantly, due to the thin nitrogen-doped carbon layer, NiCoP@NC/NF showed considerably enhanced stability under the harsh conditions of long-term reaction. Density functional theory (DFT) calculations have indicated that the nitrogen-doped carbon of NiCoP@NC/NF permitted moderate trapping of hydrogen atoms and easy desorption of the resulting H2. Such impressive HER performance of the hybrid electrocatalyst is mainly attributed to the collective effects of elemental doping engineering between NC and NiCoP, the enlarged surface area/exposed catalytic active sites, and the lower transfer resistance due to the nitrogen-doping carbon. The present work proposed a controllable and feasible strategy for synthesizing bimetallic phosphides with unique morphology and high HER performance.

Optimized loading of ultracold Cs atoms in a magnetic levitated optical dipole trap

We presented a comprehensive study of optimized loading of ultracold Cs atoms in a magnetic levitated crossed dipole trap. Moreover, we analyzed the optimized experimental parameters of the dipole laser for the opening time and the power intensity prior to switching on the magnetic field which formed the magnetically levitated dipole trap. The number of atoms as the function of sweep time from distinct laser power intensity to a fixed one is measured. And beyond that, the variation of atoms with the dipole laser power intensity per beam was studied experimentally ranging from 0 W cm−2 to a fixed one for loading the dipole trap, and the number of atoms can be increased up to a maximum of ∼1.67 × 106. Our research demonstrates that the ‘pre-loading process’ plays a crucial role in enhancing the loading efficiency of an optical dipole trap.

Investigating the Dynamics of Pt/CeO2 Catalysts at the Powder Agglomerate Scale by Combining In Situ Hyperspectral Raman Imaging and SEM‐EDX Analysis

AbstractThe dynamics of Pt/CeO2 catalysts is a hot topic since its knowledge can be used to (re)generate more active sites for redox reactions, even at low temperature (<500 °C). While numerous works focus on the atomic scale, the spatial extent of Pt surface diffusion is poorly known. In this work, it is evaluated at the powder agglomerate scale using an original methodology combining SEM‐EDX analysis and in situ optical/microRaman hyperspectral imaging performed on a Pt/CeO2+CeO2 mechanical mixture. No intergranular diffusion of platinum during redox cycles at 500 °C is revealed by these techniques, in particular by the Raman images of Ce3+ and peroxo species, which are highly sensitive to the presence of Pt atoms. It strongly suggests that Pt surface diffusion takes place only at the nanometer scale and could be limited by atom trapping on Pt/CeO2 agglomerates. Our method for investigating diffusion processes at the micrometer scale may be extended to other thermochemical conditions and other materials.

Antihydrogen and Hydrogen: Search for the Difference

Our universe consists mainly of regular matter, while the amount of antimatter seems to be negligible. The origin of this difference, known as the baryon asymmetry, remains undiscovered. Since the discovery of antimatter, many experiments have been carried out to study antiparticles and to compare matter and antimatter twins. Two of the most sensitive methods in physics, radiofrequency and optical spectroscopy, can be efficiently used to search for the difference. The successful synthesis and trapping of cold antihydrogen atoms opened the possibility of significantly increasing the sensitivity of matter/antimatter tests. This brief review focuses on a hydrogen/antihydrogen comparison using other independent spectroscopic measurements of single particles in traps and other simple atomic systems like positronium. Although no significant difference is detected in today’s level of accuracy, one can push forward the sensitivity by improving the accuracy of 1S–2S positronium spectroscopy, spectroscopy of hyperfine transition in antihydrogen, and gravitational measurements.

Two-dimensional magneto-optical trap of dysprosium atoms as a compact source for efficient loading of a narrow-line three-dimensional magneto-optical trap

Two-dimensional magneto-optical trap of dysprosium atoms as a compact source for efficient loading of a narrow-line three-dimensional magneto-optical trap

First-Principles Study of the Stability of Ti n O m Clusters and He Behavior Inside Ti n O2Va1 Clusters in Vanadium Alloy

In order to characterize the behaviors of interstitial oxygen (O) in the vanadium (V) alloy, the interactions between O and Ti with respect to atomic separation distance have been investigated using first-principles calculations. We observe an attractive interaction between Ti and O within the third nearest neighbor (nn) (3nn) distance. The stability of the Ti-vacancy (Ti-Va) clusters has been studied by calculating the binding energy between Ti and monovacancy in the vanadium alloy, and our results show that the stable configurations are Ti1Va1, Ti2Va1, and Ti4Va1 clusters. The TinVa1 clusters prefer to trap two O atoms and form stable Ti1O2Va1, Ti2O2Va1, and Ti4O2Va1 clusters. Furthermore, the self-trapping energies of the Hex clusters by the TinO2Va1 clusters have been calculated. When four He atoms are trapped, the Hex clusters are stable. Furthermore, the trapping energies for the multiple He atoms captured by the TinO2Va1 clusters are calculated, and the TinO2 clusters are found to impede the vacancy trapping of He atoms to form He bubbles.

Magic wavelengths for the 6S-7P transition of cesium atoms

For the trapped pre-cooled atoms in an optical dipole trap (ODT), the magic-wavelength ODT can eliminate the differential light shift of the transition between two atomic states, so that the transition frequency between the two states is the same as that of atoms in the free space, which is of great significance for improving the experimental repetition rate and reducing the atomic decoherence in the fields of cold atom physics, quantum optics, and precision measurement. Here we calculate the dynamic polarizabilities of cesium 6S ground state and 7P excited state by using the multi-level model for the ODT with laser wavelength from 1200 to 2000 nm. The magic wavelengths of ODT are obtained for the linearly and circularly polarized laser beams at the intersection of dynamic polarizabilities of two atomic states. Furthermore, we analyze the robustness of the magic trapping conditions and the feasibility of the experimental operation near the telecom C-band wavelength.

A hybrid mechanism of 3D optical trapping of particles immersed in a cold buffer gas

A novel mechanism of the formation of a deep optical superlattice (OSL) for three-dimensional (3D) trapping of resonant impurity atoms immersed in a transparent cold buffer gas is proposed and investigated theoretically. This mechanism is associated with the joint action of two factors of different physical nature: rectification effect of the gradient force of light pressure and effect of the light induced drift (LID) of atoms (a consequence of the difference in gas-kinetic cross sections of excited and unexcited atoms). Such a situation can be realised when a gas mixture is irradiated by a bichromatic combined light beam which is a special coaxial superposition of cosine-Gaussian optical beams. Here, the RcGF creates a periodic 1D array of deep potential wells (OSL) along the beam axes, and an effective force, causing LID, pulls resonant particles into the combined light beam and provides their transverse (with respect to the beam axes) confinement in OSL. As a result, there can occur a giant accumulation of impurity particles in the OSL cells, accompanied by a strong spatial particle localization far away from the walls of the reservoir, in which the gas mixture is located.

High efficient Raman sideband cooling and strong three-body recombination of atoms

We report a highly efficient three-dimensional degenerated Raman sideband cooling (3D dRSC) that enhances the loading of a magnetically levitated optical dipole trap, and observe the strong atom loss due to the three-body recombination. The 3D dRSC is implemented to obtain 5 × 107 Cs atoms with the temperature of ∼ 480 nK. The cold temperature enables 1.8 × 107 atoms loaded into a crossed dipole trap with an optimized excessive levitation magnetic gradient. Compared to the loading of atoms from a bare magneto-optical trap or the gray-molasses cooling, there is a significant increase in the number of atoms loaded into the optical dipole trap. We derive for the three-body recombination coefficient of L 3 = 7.73 × 10−25 cm6/s by analyzing the strong atom loss at a large scattering length of 1418 Bohr radius, and discover the transition from the strong three-body loss to the dominant one-body loss. Our result indicates that the lifetime of atoms in the optical dipole trap is finally decided by the one-body loss after the initial strong three-body loss.

Numerical analysis of hydrogen atom diffusion and trapping at an unconstrained dent on pipelines

In this work, a three-dimensional finite element-based mechanics-diffusion coupling model is developed to determine the stress/strain distribution and hydrogen (H) atom concentration at an unconstrained dent on an X52 steel pipe which is to be used for transport of high-pressure hydrogen gas. Both von Mises stress and equivalent plastic strain concentrations and a high hydrostatic stress gradient exist at the dent. The distribution of H atom concentration coincides with that of the hydrostatic stress. The maximum H atom concentration in the steel lattice locates at the dent bottom, while the distribution of the H atom concentration at metallurgical traps is consistent with that of the equivalent plastic strain. A competitive effect exists between the hydrostatic stress and the plastic strain on the H atom distribution. At low initial H atom concentrations (e.g., 0.001 mol/m3), the equivalent plastic strain dominates the distribution of H atoms. At high initial H atom concentrations (e.g., 0.1 and 1 mol/m3), the hydrostatic stress is more important to determine the distribution of H atom concentration. As the dent depth increases, both the von Mises stress and plastic strain at the dent increases, while the total H atom concentration decreases due to decreased hydrostatic stress. When the internal pressure increases from 5 MPa to 15 MPa, there are slightly increases in von Mises stress, equivalent plastic strain and the total H atom concentration.

T-cut slotted quartz tube-atom trap strategy for the on-line preconcentration of thallium in well water samples

In this study, an on-line preconcentration system was developed for the quantitative determination of thallium in well water samples using hydrogen-assisted T-cut slotted quartz tube atom trapping (HA-T-SQT-AT) coupled to flame atomic absorption spectrometry (FAAS). The method is based on trapping the thallium atoms on the inner surface of the T-SQT for a short period using sample aspiration and lean flame conditions. Then, hydrogen gas as a reducing agent was released instantly to free the trapped analyte atoms, resulting in a sharp and narrow signal. The system analytical performance was enhanced by performing comprehensive optimization of several factors. The linear range and LOD/LOQ values of the optimized method were found to be 7.5–––200 ng/mL and 2.6/8.7 ng/mL, respectively. Accuracy/practicability of the presented method were verified using well water samples, and the percent recoveries calculated using the external calibration approach were all above 80%.

Corrections to local-density approximation for superfluid trapped fermionic atoms from the Wigner-Kirkwood $$\hbar $$ expansion

Corrections to local-density approximation for superfluid trapped fermionic atoms from the Wigner-Kirkwood $$\hbar $$ expansion

Generation of a Focused THz Vortex Beam from a Spintronic THz Emitter with a Helical Fresnel Zone Plate.

Similar to optical vortex beams, terahertz (THz) vortex beams (TVBs) also carry orbital angular momentum (OAM). However, little research has been reported on the generation of TVBs. In this paper, based on the detour phase technique, we design a series of spintronic terahertz emitters with a helical Fresnel zone plate (STE-HFZP) to directly generate focused TVBs with topological charges (TCs) of l = ±1, ±2 and ±3, respectively. The STE-HFZP is a hybrid THz device composed of a terahertz emitter and a THz lens, and it has a high numerical aperture (NA), achieving subwavelength focal spots. Its focus properties are surveyed systemically through accurate simulations. This STE-HFZP can also generate focused TVBs with higher order TCs. More importantly, the components of the focused electric field with OAM make up the majority of the intensity and have potential applications in the field of THz communications, THz imaging and atom trapping.

Bloch oscillations along a synthetic dimension of atomic trap states

Bloch oscillations along a synthetic dimension of atomic trap states

Single atom in a superoscillatory optical trap

Optical tweezers have become essential tools to manipulate atoms or molecules at a single particle level. However, using standard diffraction-limited optical systems, the transverse size of the trap is lower bounded by the optical wavelength, limiting the application range of optical tweezers. Here we report trapping of single ultracold atom in an optical trap that can be continuously tuned from a standard Airy focus to a subwavelength hotspot smaller than the usual Abbe’s diffraction limit. The hotspot was generated using the effect of superoscillations, by the precise interference of multiple free-space coherent waves. We argue that superoscillatory trapping and continuous potential tuning offer not only a way to generate compact and tenable ensembles of trapped atoms for quantum simulators but will also be useful in single molecule quantum chemistry and the study of cooperative atom-photon interactions within subwavelength arrays of quantum emitters.

Upgradation of fission gas release model in the nuclear fuel analysis code FuSPAC

The evaluation of fuel performances in the whole life cycle is important to the fuel integrity. In our previous work, a fuel performance analysis code FuSPAC was developed and validated against the in-pile test data and FRAPCON code. In the current work, this code was upgraded by replacing the modified Forsberg-Massih for fission gas release (FGR) with a mechanism model. The microscopic behaviors related to the FGR, including the gas atom diffusion, trapping, re-solution and bubble nucleation inside the granular particles, the vacancy diffusion at the inter-granular boundaries, the grain growth and the grain recrystallization were modeled. The upgraded FuSPAC code was validated against the in-pile test data for FGR and internal void volume. The sensitivity analysis on the sub-models shown that the intra-granular fission gas diffusion, the re-solution, and the inter-granular vacancy diffusion had significant effects on the FGR. The effects from rod power can be well reflected by the upgraded code compared to the original code.

Characterization of a forced damped harmonic oscillator in a magneto-optical trap of 133Cs atoms

We report the characterization of the forced damped harmonic oscillations of 133Cs atoms in a magneto-optical trap, which was realized by modulating the intensity of the lasers counterpropagating along the anti-Helmholtz coil axis. Trap parameters such as trap frequency, damping coefficient, and magnitude of the driving force were determined from the resonant vibrational amplitude of the 133Cs atomic cloud depending on the modulation frequency of the modulated laser intensity. The experimental results were compared with the theoretical ones based on the simple two-level and multi-level atom models, considering all possible transition lines used to trap the 133Cs atom, and were found to be consistent with their theoretical counterparts. Furthermore, we theoretically examined the effect of the repumping laser on trap parameters.

Time-orbiting-potential chip trap for cold atoms

We present a design for an atom chip trap that uses the time-orbiting potential technique. The design offers several advantages compared to other chip-trap methods. It uses a simple crossed-wire pattern on the chip, along with a rotating bias field. The trap is naturally close to spherically symmetric, and it can be modified to be exactly symmetric in quadratic order of the coordinates. Loading from a magneto-optical trap is facilitated because the trap can be positioned an arbitrary distance from the chip. The fields can be modified to provide a gradient for support against gravity, and the three-dimensional trap can be adiabatically transformed into a two-dimensional guide.

Development of a New Sensitive Method for Lead Determination by Platinum-Coated Tungsten-Coil Hydride Generation Atomic Absorption Spectrometry.

A novel very sensitive and rapid analytical method was improved where gaseous lead formed was transported to and trapped on an externally heated platinum-coated tungsten-coil atom trap for in situ preconcentration. The analytical performance of the developed method with the graphite furnace atomic absorption spectrometry (GFAAS) method was compared. All critical parameters affecting the performance of both methods were optimized. The limit of quantitation (LOQ) was found as 11.0 ng L-1 and the precision was 2.3% in terms of percent relative standard deviation (RSD%). Characteristic concentration (Co) of the developed trap method was indicating a 32.5-fold enhancement in sensitivity compared to the GFAAS method. In order to investigate the surface morphology of the W-coil, scanning electron microscope-energy-dispersive X-ray (SEM-EDS) analyzes were performed. The accuracy of the trap method was tested by certified reference materials: NIST SRM 1640a (the elements in natural water) and DOLT:5 (dogfish liver). Interferences from other hydride-forming elements were investigated. Application of the trap method was demonstrated by the analysis of some drinking water and fish tissue samples. The t test was applied to drinking water samples, and the results indicated that there was no statistically significant error.

Point singularity array with metasurfaces

Phase singularities are loci of darkness surrounded by monochromatic light in a scalar field, with applications in optical trapping, super-resolution imaging, and structured light-matter interactions. Although 1D singular structures, like optical vortices, are common due to their robust topological properties, uncommon 0D (point) and 2D (sheet) singularities can be generated by wavefront-shaping devices like metasurfaces. With the design flexibility of metasurfaces, we deterministically position ten identical point singularities using a single illumination source. The phasefront is inverse-designed using phase-gradient maximization with an automatically-differentiable propagator and produces tight longitudinal intensity confinement. The array is experimentally realized with a TiO2 metasurface. One possible application is blue-detuned neutral atom trap arrays, for which this field would enforce 3D confinement and a potential depth around 0.22 mK per watt of incident laser power. We show that metasurface-enabled point singularity engineering may significantly simplify and miniaturize the optical architecture for super-resolution microscopes and dark traps.