Trapping Of Atoms Research Articles

Limitation of single-repumping schemes for laser cooling of Sr atoms

We explore the efficacy of two single-repumping schemes, 5s5pP23−5p2P23 (481nm) and 5s5pP23−5s5dD23 (497nm), for a magneto-optical trap (MOT) of Sr atoms. We reveal that the enhancement in the MOT lifetime is limited to 26.9(2) for any single-repumping scheme. Our investigation indicates that the primary decay path from the 5s5pP11 state to the 5s5pP03 state proceeds via the 5s4dD13 state, rather than through the upper states accessed by the single-repumping lasers. We estimate that the branching ratio for the 5s5pP11→5s4dD13→5s5pP03 decay path is 1:3.9(1.5)×106 and the decay rate for the transition from the 5s5pP11 state to the 5s4dD13 state is 83(32)s−1. This outcome underscores the limitation on atom number in the MOT for long loading times (≳1s) when employing a single-repumping scheme. These findings will contribute to the construction of field-deployable optical lattice clocks. Published by the American Physical Society 2024

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.

Static disorder in perovskite-type proton-conducting oxides BaSn1-xMxO3-x/2-(y/2)H2O (M = Ga, Sc, In, Y, La): a novel approach based on statistical analysis of numerous DFT simulated structures.

Perovskite-type proton-conducting oxides inherently include defects such as substitutional aliovalent cations, oxide ion vacancies, and interstitial protons. These defects introduce static disorder into their crystal structures. To investigate such disorder in BaSn1-xMxO3-x/2-(y/2)H2O (M = Ga, Sc, In, Y, La), we employ a novel approach based on density functional theory (DFT) simulations. This approach involves the structural optimization of a large number of relatively small, randomly constructed supercells, followed by statistical analysis of their geometric, energetic, and vibrational properties. Our key findings are as follows. The structural disorder becomes more pronounced as the dopant concentration increases, and as the dopant ionic radius increases from Sc to La. The O-H covalent bond lengths, as well as the number densities, of hydrogen atoms display clearly different distributions depending on whether the hydrogen atoms are trapped by aliovalent cations or not. The hydrogen-trapping energies appear to decrease as the geometric similarity of O-H covalent bonds between trapped and untrapped hydrogen atoms increases. Hydrogen atoms simultaneously trapped by more than one dopant atom exhibit considerable stability, potentially hindering proton diffusion at high dopant concentrations. The O-H stretching wavenumber decreases as the O-H covalent bond length increases, showing a very strong and nearly linear correlation between the two. The simulated IR absorption spectra show semi-quantitative agreement with the measured spectra. These new findings demonstrate the effectiveness of the present 'statistical' approach for investigating static disorder.

Plasma‐electrified synthesis of atom‐efficient electrocatalysts for sustainable water catalysis and beyond

The downsizing of metal structures to the nano and atomic level, thereby creating nanoparticle catalysts (NPCs), sub‐nanometer cluster catalysts (SNCCs) or single atom catalysts (SACs), has gained significant interest. In particular, synthesizing these types of catalysts using low temperature plasma electrified methods is an emerging field which is highly applicable to electrochemical water splitting for the sustainable production of green hydrogen. Surface modification via plasma treatment provides a route for nanoparticle immobilization or single atom trapping which ensures high atom utilization during electrolysis reactions. Plasma can also be used to create NPCs, SNCCs and SACs from various precursors as well as modify their surface properties once formed which impacts significantly on the oxygen evolution reaction and hydrogen evolution reaction. Therefore, in this review we emphasize the role that low temperature plasma electrified synthetic strategies play in electrocatalyst development for water splitting reactions and explore the crucial relationship between the electronic and coordination environment of atom efficient catalysts and their resulting catalytic activity. We also discuss methods to characterize these types of catalysts and the possibility for scaling up this technology which will be required for commercial applications.

Intrinsic angular momentum, spin and helicity of higher-order Poincaré modes

Abstract The availability of coherent sources of higher order Poincaré optical beams have opened up new opportunities for applications such as in the optical trapping of atoms and small particles, the manipulation of chirally-sensitive systems and in improved encoding schemes for broad-bandwidth communications. Here we determine the intrinsic properties of integer order m ⩾ 0 Poincaré Laguerre–Gaussian (LG) modes which have so far neither been evaluated, nor their significance highlighted. The theoretical framework we adopt here is both novel and essential because it emphasises the crucial role played by the normally ignored axial components of the twisted light fields of these modes. We show that the inclusion of the axial field components enables the intrinsic properties of the Poincaré modes, notably their angular momentum, both spin and orbital as well as their helicity and chirality, to be determined. We predict significant enhancements of the intrinsic properties of these modes when compared with those due to the zero order LG modes. In particular, we show that higher order LG Poincaré modes exhibit super-chirality and, significantly so, even in the case of the first order m = 1.

Cavity Floquet engineering

Floquet engineering is a promising tool to manipulate quantum systems coherently. A well-known example is the optical Stark effect, which has been used for optical trapping of atoms and breaking time-reversal symmetry in solids. However, as a coherent nonlinear optical effect, Floquet engineering typically requires high field intensities obtained in ultrafast pulses, severely limiting its use. Here, we demonstrate using cavity engineering of the vacuum modes to achieve orders-of-magnitude enhancement of the effective Floquet field, enabling Floquet effects at an extremely low fluence of 450 photons/μm2. At higher fluences, the cavity-enhanced Floquet effects lead to 50 meV spin and valley splitting of WSe2 excitons, corresponding to an enormous time-reversal breaking, non-Maxwellian magnetic field of over 200 T. Utilizing such an optically controlled effective magnetic field, we demonstrate an ultrafast, picojoule chirality XOR gate. These results suggest that cavity-enhanced Floquet engineering may enable the creation of steady-state or quasi-equilibrium Floquet bands, strongly non-perturbative modifications of materials beyond the reach of other means, and application of Floquet engineering to a wide range of materials and applications.

In-situ formed stable Pt nanoclusters on ceria-zirconia solid solutions induced by hydrothermal aging for efficient low-temperature CO oxidation

Pt nanoclusters (PtC) on the surface of ceria-zirconia solid solutions exhibit superior low-temperature CO oxidation activity compared to Pt single atoms (Pt1). However, the redispersion behavior of the PtC to Pt1 lowers the efficiency of CO Oxidation. In this work, the stable surface hydroxyl groups were constructed by high-temperature hydrothermal aging treatment. Specifically, the Pt1 catalyst (Pt/CZOe-SA) prepared by atom trapping was subjected to high-temperature hydrothermal treatment to obtain the stable PtC catalyst (Pt/CZOe-HT) with in-situ formed PtC. The experimental results showed that PtC with 2–3 nm size could achieve excellent low-temperature activity and thermal stability. In addition, the ab initio molecular dynamics and density functional theory calculations revealed the specific evolution process of dynamic dispersion for PtC with or without hydroxyl groups from the femtosecond scale, suggesting that the hydroxyl groups limited the dispersion of PtC in the form of “energy fence”. The hydrothermal treatment not only introduced high-temperature stable hydroxyl groups to improve the stability of the in-situ formed PtC, but also optimized the ratio of Pt1 and PtC, and then enhanced the low-temperature activity by the synergistic effect between Pt1 and PtC. The present work can provide theoretical guidance for developing high-performance and high-stability Pt-based catalysts.

Realization of a chip-based hybrid trapping setup for 87Rb atoms and Yb+ ion crystals.

Hybrid quantum systems integrate laser-cooled trapped ions and ultracold quantum gases within a single experimental configuration, offering vast potential for applications in quantum chemistry, polaron physics, quantum information processing, and quantum simulations. In this study, we introduce the development and experimental validation of an ion trap chip that incorporates a flat atomic chip trap directly beneath it. This innovative design addresses specific challenges associated with hybrid atom-ion traps by providing precisely aligned and stable components, facilitating independent adjustments of the depth of the atomic trapping potential, and positioning trapped ions. Our findings include the simultaneous loading of the ion trap with linear Yb+ ion crystals and the loading of neutral 87Rb atoms into a mirror magneto-optical trap.

Two mass-imbalanced atoms in a hard-wall trap: Deep learning integrability of many-body systems.

The study of integrable systems has led to significant advancements in our understanding of many-body physics. We design a series of numerical experiments to analyze the integrability of a mass-imbalanced two-body system through energy-level statistics and deep learning of wave functions. The level spacing distributions are fitted by a Brody distribution and the fitting parameter ω is found to separate the integrable and nonintegrable mass ratios by a critical line ω=0. The convolutional neural network built from the probability density images could identify the transition points between integrable and nonintegrable systems with high accuracy, yet in a much shorter computation time. A brilliant example of the network's ability is to identify a new integrable mass ratio 1/3 by learning from the known integrable case of equal mass, with a remarkable network confidence of 98.22%. The robustness of our neural networks is further enhanced by adversarial learning, where samples are generated by standard and quantum perturbations mixed in the probability density images and the wave functions, respectively.

Investigating the impact of alloying elements on hydrogen diffusion in Ti-based alloys via first-principles calculations

The diffusion of hydrogen in Ti-based alloys can lead to localized degradation of mechanical properties, resulting in hydrogen embrittlement. Therefore, identifying alloying elements that impede hydrogen diffusion is a crucial approach to mitigating hydrogen embrittlement and stress corrosion in Ti-based alloys. Utilizing first-principles calculations, we investigated the effects of 33 alloying elements on hydrogen diffusion in Ti-based alloys, including diffusion barriers and coefficients. Our findings demonstrate that elements such as Al, Ga, Si, and Zn increase the hydrogen diffusion barriers and decrease the diffusion coefficients in Ti-based alloys, thereby mitigating hydrogen embrittlement. It is revealed that the difference of electronegativity of Al, Si, Au, Ag, Pd, Ir, Zn, and Cu affects the hydrogen atom trapping ability. It also sheds light on strategies to mitigate hydrogen embrittlement in Ti-based alloys. This insight highlights their significant role in hindering the movement of hydrogen atoms within the alloys.

Effect of light-assisted tunable interaction on the position response function of cold atoms.

The position response of a particle subjected to a perturbation is of general interest in physics. We study the modification of the position response function of an ensemble of cold atoms in a magneto-optical trap (MOT) in the presence of tunable light-assisted interactions. We subject the cold atoms to an intense laser light tuned near the photoassociation (PA) resonance and observe the position response of the atoms subjected to a sudden displacement. Surprisingly, we observe that the entire cold atomic cloud undergoes collective oscillations. We use a generalized quantum Langevin approach to theoretically analyze the results of the experiments and find good agreement.

Non-transverse electromagnetic fields in micro- and nano-fibers

We present an analytical and numerical study of electromagnetic modes in micro- and nano-fibers (MNFs) where the electric and magnetic fields of the modes are not necessarily orthogonal to each other. We first investigate these modes for different fiber structures including circular- and rectangular-core fibers as well as photonic crystal fibers. We then discuss two specific applications of these modes: (1) generation of hypothetical axions that are coupled to the electromagnetic fields through the dot product of electric and magnetic fields of a mode, E→⋅B→, and (2) a new type of optical trap (optical tweezers) for chiral atoms with magneto-electric cross coupling, where the confining potential again is proportional to E→⋅B→.

Synthesis of ultrahigh-metal-density single-atom catalysts via metal sulfide-mediated atomic trapping

Synthesis of ultrahigh-metal-density single-atom catalysts via metal sulfide-mediated atomic trapping

Accelerating analysis of Boltzmann equations using Gaussian mixture models: Application to quantum Bose-Fermi mixtures

The Boltzmann equation is a powerful theoretical tool for modeling the collective dynamics of quantum many-body systems subject to external perturbations. Analysis of the equation gives access to linear response properties including collective modes and transport coefficients, but often proves intractable due to computational costs associated with multidimensional integrals describing collision processes. Here, we present a method to resolve this bottleneck, enabling the study of a broad class of many-body systems that appear in fundamental science contexts and technological applications. Specifically, we demonstrate that a Gaussian mixture model can accurately represent equilibrium distribution functions, thereby allowing efficient evaluation of collision integrals. Inspired by cold atom experiments, we apply this method to investigate the collective behavior of a quantum Bose-Fermi mixture of cold atoms in a cigar-shaped trap, a system that is particularly challenging to analyze. We focus on monopole and quadrupole collective modes above the Bose-Einstein transition temperature, and find a rich phenomenology that spans interference effects between bosonic and fermionic collective modes, dampening of these modes, and the emergence of hydrodynamics in various parameter regimes. These effects are readily verifiable experimentally. Published by the American Physical Society 2024

Non-equilibrium solidification of undercooled Inconel 718

The non-equilibrium solidification of undercooled Inconel 718 melts has been studied in situ on electromagnetically levitated samples by using high-speed video recording and optical pyrometry. Microstructure and phase constitution of solidified samples were analysed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscatter diffraction and high-energy X-ray diffraction. Due to containerless sample processing experimental data on phase formation, γ-dendrite growth, and microstructural evolution in Inconel 718 were obtained over a wide range of undercooling ΔT between 20 and 289 K. It has been found that the dendrite growth velocity, extracted from high-speed video records, rises exponentially with increasing undercooling at first. At an undercooling of about 150 K, growth slows down drastically. Furthermore, morphology and size of γ-matrix grains essentially depend on ΔT. They alter from coarse equiaxed to coarse columnar at an undercooling of about 60 K, get refined and equiaxed at undercoolings above 150 K, and become larger and elongated again upon reaching an undercooling of about 250 K. The deviation from equilibrium and trapping of solute atoms in γ-dendrites result in a notable reduction of NbC and Laves fraction, the latter apparently disappearing at ΔT larger than 150 K.

Background-free imaging of cold atoms in optical traps

Optical traps, including those used in atomic physics, cold chemistry, and quantum science, are widely used in the research on cold atoms and molecules. Owing to their microscopic structure and excellent operational capability, optical traps have been proposed for cold atom experiments involving complex physical systems, which generally induce violent background scattering. In this study, using a background-free imaging scheme in cavity quantum electrodynamics systems, a cold atomic ensemble was accurately prepared below a fiber cavity and loaded into an optical trap for transfer into the cavity. By satisfying the demanding requirements for the background-free imaging scheme in optical traps, cold atoms in an optical trap were detected with a high signal-to-noise ratio while maintaining atomic loading. The cold atoms were then transferred into the fiber cavity using an optical trap, and the vacuum Rabi splitting was measured, facilitating relevant research on cavity quantum electrodynamics. This method can be extended to related experiments involving cold atoms and molecules in complex physical systems using optical traps.

Controlling the interactions in a cold atom quantum impurity system

We implement an experimental architecture in which a single atom of K is trapped in an optical tweezer, and is immersed in a bath of Rb atoms at ultralow temperatures. In this regime, the motion of the single trapped atom is confined to the lowest quantum vibrational levels. This realizes an elementary and fully controllable quantum impurity system. For the trapping of the K atom, we use a species-selective dipole potential, that allows us to independently manipulate the quantum impurity and the bath. We concentrate on the characterization and control of the interactions between the two subsystems. To this end, we perform Feshbach spectroscopy, detecting several inter-dimensional confinement-induced Feshbach resonances for the KRb interspecies scattering length, that parametrizes the strength of the interactions. We compare our data to a theory for inter-dimensional scattering, finding good agreement. Notably, we also detect a series of p-wave resonances stemming from the underlying free-space s-wave interactions. We further determine how the resonances behave as the temperature of the bath and the dimensionality of the interactions change. Additionally, we are able to screen the quantum impurity from the bath by finely tuning the wavelength of the light that produces the optical tweezer, providing us with a new effective tool to control and minimize the interactions. Our results open a range of new possibilities in quantum simulations of quantum impurity models, quantum information, and quantum thermodynamics, where the interactions between a quantized system and the bath is a powerful yet largely underutilized resource.

Metasurface optical trap array for single atoms

Metasurfaces made of subwavelength silicon nanopillars provide unparalleled capacity to manipulate light, and have emerged as one of the leading platforms for developing integrated photonic devices. In this study, we report on a compact, passive approach based on planar metasurface optics to generate large optical trap arrays. The unique configuration is achieved with a meta-hologram to convert a single incident laser beam into an array of individual beams, followed up with a metalens to form multiple laser foci for single rubidium atom trapping. We experimentally demonstrate two-dimensional arrays of 5 × 5 and 25 × 25 at the wavelength of 830 nm, validating the capability and scalability of our metasurface design. Beam waists ∼1.5 µm, spacings (about 15 µm), and low trap depth variations (8%) of relevance to quantum control for an atomic array are achieved in a robust and efficient fashion. The presented work highlights a compact, stable, and scalable trap array platform well-suitable for Rydberg-state mediated quantum gate operations, which will further facilitate advances in neutral atom quantum computing.

Spectroscopy of the 5s5p3P0→5s5d3D1 transition of strontium using laser cooled atoms

This article presents spectroscopy results of the 5s5p3P0→5s5d3D1 transition in all isotopes of laser cooled Sr atoms and the utility of this transition for repumping application. By employing the 5s5p3P0→5s5d3D1 (483 nm) transition in combination with the excitation of 5s5p3P2→5s6s3S1 (707 nm) transition, we observe a significant increase (∼13 fold) in the steady state number of atoms in the magneto-optic trap. This enhancement is attributed to the efficient repumping of Sr atoms that have decayed into the dark 5s5p3P2 state by returning them to the ground state 5s21S0 without any loss into the other states. The absolute transition frequencies were measured with an absolute accuracy of 30 MHz. To support our measurements, we performed Fock-space relativistic coupled-cluster calculations of the relevant parameters in Sr To further increase the accuracy of the calculated properties, corrections from the Breit, quantum electrodynamical and perturbative triples were also included. The calculated branching ratio for the repumping state confirms the significantly increased population in the 3P1 state. Thereby, leading to an increase of population of atoms trapped due to the enhanced repumping. Our calculated hyperfine-splitting energies are in excellent agreement with the measured values. Moreover, our calculated isotope shifts in the transition frequencies are in good agreement with our measured values.

Thermodynamics and kinetics of interconversion between platinum nanoparticles and cations in zeolites

In metal-containing zeolites, sintering and redispersion processes exercise control over the identity of metal site structures, but the thermodynamic and kinetic factors that influence these molecular-level processes are not completely understood. Here, we assess the ability of first principles informed free energy models (for supported and unsupported nanoparticles) and kinetic models integrating Ostwald ripening with atom trapping to describe the interconversion between Pt cations and nanoparticles encapsulated in chabazite (CHA) zeolites. Density functional theory-derived thermodynamic phase diagrams show that the interconversion between cations, favored in oxidizing environments, and particles, favored in reducing environments, is fully reversible within a wide range of their respective conditions (temperatures and pressures) for CHA and several other zeolite topologies. Kinetic Monte Carlo simulations of Pt redispersion are consistent with experimentally observed redispersion kinetics of encapsulated Pt nanoparticles in CHA zeolites, and model results suggest the zeolite host imparts additional stability for Pt nanoparticles. We envision our thermodynamic and kinetic models for Pt-CHA are also capable of describing nanoparticle and cation interconversions for other zeolite frameworks under similar conditions.