Mixture Of Atoms Research Articles

Berezinskii-Kosterlitz-Thouless phase transition with Rabi-coupled bosons

We theoretically investigate the superfluid-normal-state Berezinskii-Kosterlitz-Thouless transition in a binary mixture of bosonic atoms with Rabi coupling under balanced densities. We find the nonmonotonic behavior of the transition temperature with respect to the intercomponent coupling and amplification of the transition temperature for finite values of Rabi coupling, but for small intracomponent couplings. We develop the Nelson-Kosterlitz renormalization-group equations in the two-component Bose mixture and obtain the Nelson-Kosterlitz criterion modified by a fractional parameter, which is responsible for half-integer vortices, and by Rabi coupling. Adopting the renormalization-group approach, we clarify the dependence of the Berezinskii-Kosterlitz-Thouless transition temperature on the Rabi coupling and the intercomponent coupling. Analysis of the first and second sound velocities also reveals the suppression of quasicrossing of the two sound modes with a finite Rabi coupling in the low-temperature regime. Our results for a two-dimensional binary Bose superfluid contribute to the understanding of a broad range of multicomponent quantum systems such as two-dimensional multiband superconductors.

"Ideal'nost'" "neideal'noy" plazmy

Two chemical models of the plasma, which describe the mixture of free electrons, ions, and atoms, are derived using identity transformations based on the equation of state of the “physical” model of the plasma, in which an interacting mixture of electrons and nuclei (protons) us considered. These chemical models satisfy Onsager’s bookkeeping rule (the equation of state is independent on the position of the bookmark, viz., the boundary separating free and bound states). The effect of excited states of an atom on the equation of state and ionization equilibrium is analyzed. It is concluded that the contribution of the Debye attraction in traditional “chemical” models is overestimated. The relations obtained for the ionization potential lowering and the equations of state differ significantly from the generally accepted expressions and explain qualitatively the experimentally observed effect of “ideality” of a nonideal plasma.

Quasiclassical study of a termolecular reaction: A more detailed description of the HO2 collisional stabilization process

We present detailed studies of the collisional stabilization of the HO2∗ radical in a mixture of hydrogen atoms and oxygen molecules using molecular dynamic studies and accurate potential energy surfaces. Following previous work on this process’s global temperature and pressure dependencies, we analyze each collider’s role and estimate specific rate constants and their temperature dependence.

Ultrahigh Mass Activity Pt Entities Consisting of Pt Single atoms, Clusters, and Nanoparticles for Improved Hydrogen Evolution Reaction.

Platinum is one of the best-performing catalysts for the hydrogen evolution reaction (HER). However, high cost and scarcity severely hinder the large-scale application of Pt electrocatalysts. Constructing highly dispersed ultrasmall Platinum entities is thereby a very effective strategy to increase Pt utilization and mass activities, and reduce costs. Herein, highly dispersed Pt entities composed of a mixture of Pt single atoms, clusters, and nanoparticles are synthesized on mesoporous N-doped carbon nanospheres. The presence of Pt single atoms, clusters, and nanoparticles is demonstrated by combining among others aberration-corrected annular dark-field scanning transmission electron microscopy, X-ray absorption spectroscopy, and electrochemical CO stripping. The best catalyst exhibits excellent geometric and Pt HER mass activity, respectively ≈4 and 26 times higher than that of a commercial Pt/C reference and a Pt catalyst supported on nonporous N-doped carbon nanofibers with similar Pt loadings. Noteworthily, after optimization of the geometrical Pt electrode loading, the best catalyst exhibits ultrahigh Pt and catalyst mass activities (56 ± 3 A mg-1 Pt and 11.7 ± 0.6 A mg-1 Cat at -50mV vs. reversible hydrogen electrode), which are respectively ≈1.5 and 58 times higher than the highest Pt and catalyst mass activities for Pt single-atom and cluster-based catalysts reported so far.

Nonequilibrium dynamics of fluctuations in an ultracold atomic mixture

The nonequilibrium spin-changing dynamics of an ultracold mixture of lithium and sodium atoms reveals the importance of spin fluctuations for key observables. The authors show that the experimental control of fluctuations can give access to the dynamics of a long-lived metastable state, an instability region with strong growth of fluctuations, and a regime with an early approach to thermal equilibrium.

Peng: A program for transport properties of low-density binary gas mixtures

The fundamental properties of molecules bridge experiment and theory. Transport properties (diffusion, thermal diffusion, thermal conductivity and viscosity) of binary mixtures are measurable in experiments, and well-defined in theory, but difficult to compute with high accuracy. In addition to high-accuracy inter-molecular potential energy curves (PECs), a reliable and high-order solution program that compute the properties based on the PECs is required. In this work, we present a computer program called Peng that performs the collision integration numerically, and solves the Boltzmann equation in Chapman–Enskog fashion. The program has been devised to perform both parts of the solution procedure to arbitrary order, so that no hard-coded limitation will prevent a user from computing at higher precision, except the amount of RAM and the required computational time. Peng is well-designed in an Object-Oriented Programming (OOP) fashion, which make the program clear and easy to modify. In addition to the end-user oriented program, Peng is also compiled as a dynamic shared library that may readily be extended and embedded in users' programs. Program summaryProgram Title:PengCPC Library link to program files:https://doi.org/10.17632/n5tm9426jx.1Developer's repository link:https://github.com/zhaiyusci/pengCode Ocean capsule:https://codeocean.com/capsule/9951686Licensing provisions: LGPLProgramming language: C++Nature of problem: Nowadays, quantum chemistry provides high-accuracy intermolecular interactions potential energy curves (PECs), and more and more accurate thermophysical properties of dilute gases can be measured experimentally. It is meaningful to build a bridge between thermophysical properties and PECs, so that people can refine the PECs and learn more about the nature of dynamics of gases. For a dilute binary gas mixture, the theory, the Boltzmann equation, and its solution has been available for a long time, but fewer numerical solution packages are available for the public. An easy-to-use and easy-to-extend software package is required.Solution method: To complete the work, we have created a program that computes the collision integrals (Ω(ℓ,s)) for a set of temperatures, following which the thermophysical properties are computed using the Chapman–Enskog solutions of the Boltzmann equation. Both parts of the program are written in C++. The program is easy to use, and a well-designed framework is provided thanks to the Object-oriented design. Users with programming experience can readily extend the present work.Additional comments including restrictions and unusual features: In this version, the program is limited to the computation of the properties of mixtures of structureless atoms. For polyatomic molecules, additional work need to be done.

Determination of Cr, Se, Ge, and V in Hypothyroidism Patients by Using Graphite Furnace Atomic Absorption Spectrometry and mixture matrix modification

A simple, accurate and rapid method was developed for routine determination of trace elements in blood serum. The method based on the direct determination for Cr, Se, Ge, and V in hypothyroidism patients before therapy. By using atomic absorption spectrometry with graphite surface coated and uncoated pyrolysis GF-AAS, and a mixture of palladium nitrate and magnesium nitrate as the matrix modifier, with deuterium background correction and no sample pretreatment except dilution was necessary. This permitted direct determination hence the risk of sample contamination was reduced. Further, the use of graphite surface-coated GF-AAS decreased the ashing and atomization temperatures of Cr, Ge, and V to values that were lesser than the corresponding values obtained using uncoated pyrolysis GF-AAS, by 100°C; in case of Se, the atomization temperature decreased to a value that was 200°C lesser than that obtained using uncoated pyrolysis GF-AAS.
 A mixture of (3µL) palladium nitrate, and (2µL) magnesium nitrate was successfully applied to improve the sensitivity, reproducibility, recovery, limit of detection and the accuracy of the measurements. The correlation coefficients of the calibration curves of Cr, Se, Ge, and V were found to be (0.9999, 0.9999, 0.9995 and 0.9999) respectively, the relative standard deviation of the measurements for Cr, Se, Ge and V were (0.027, 0.075, 0.054 and 0.068) respectively. The statistical analysis of the acquired data showed acceptable accuracy. The analyses thus performed indicated that the levels of serum trace elements Cr, Se, Ge, and V in hypothyroidism patients were lower than those in the control group.

Atomic boson-fermion mixtures in one-dimensional box potentials: Few-body and mean-field many-body analyses

We study binary atomic boson-fermion mixtures confined in one dimensional box potentials by few-body theory with contact interactions and mean-field many-body theory with density-density interactions. A variety of correlations and structures arise as the inter- and intraspecies interactions are tuned. Both few-body and many-body results show that miscible phase and three-chunk phase separation are directly observable in the density profiles. Meanwhile, two-chunk phase separation can be inferred from the few-body correlations and many-body density profiles. We present phase diagrams of selected types of atomic mixtures to show where different structures survive. The few-body analysis demonstrates that two-body correlation functions can reveal information relevant to the results from many-body calculations or experiments. From the many-body density profiles in the phase-separation regime, we extract the healing lengths of both species and explain the scaling behavior by an energy-competition argument.

The constraint of plasma power balance on runaway avoidance

In a post-thermal-quench plasma, mitigated or unmitigated, the plasma power balance is mostly between collisional or Ohmic heating and plasma radiative cooling. In a plasma of atomic mixture with α labeling the atomic species, the power balance sets the plasma temperature, ion charge state distribution with i the charge number, and through the electron temperature and ion charge state distribution the parallel electric field Since the threshold electric field for runaway avalanche growth is also set by the atomic mixture, ion charge state distribution and its derived quantity, the electron density the plasma power balance between Ohmic heating and radiative cooling imposes a stringent constraint on the plasma regime for avoiding and minimizing runaways when a fusion-grade tokamak plasma is rapidly terminated.

Preparation of a quantum degenerate mixture of Na23K40 molecules and K40 atoms

We report on the preparation of a quantum degenerate mixture of $^{23}\mathrm{Na}\phantom{\rule{0.16em}{0ex}}^{40}\mathrm{K}$ molecules and $^{40}\mathrm{K}$ atoms. A deeply degenerate atomic mixture of $^{23}\mathrm{Na}$ and $^{40}\mathrm{K}$ atoms with a large number ratio (${N}_{F}/{N}_{B}\ensuremath{\approx}6$) is prepared in a large-volume optical dipole trap. About $3.0\ifmmode\times\else\texttimes\fi{}{10}^{4}\phantom{\rule{0.16em}{0ex}}^{23}\mathrm{Na}\phantom{\rule{0.16em}{0ex}}^{40}\mathrm{K}$ ground-state molecules are created through magnetoassociation followed by stimulated Raman adiabatic passage. The pure molecular gas is in the moderately degenerate regime. In the atom-molecule mixture, the elastic collisions provide a thermalization mechanism for the molecules. The calculated thermalization time constant is smaller than the lifetime of the molecules in the atom-molecule mixture. This indicates that the molecules may reach thermal equilibrium due to elastic atom-molecule collisions before notable losses take place. In a few tens of milliseconds, the degeneracy of the molecules is maintained. This time interval is long enough for the study of strongly interacting atom-molecule mixtures and the production of ultracold triatomic molecular gases.

Miscibility of dual-species Bose-Einstein condensates

<sec>The miscibility of quantum liquids is an interesting topic in many-body physics, which has been intensively investigated in <sup>3</sup>He-<sup>4</sup>He superfluids and the mixtures of ultracold atoms. In the context of dual species Bose-Einstein condensates, the mean-field description has been well established, according to which, the miscibility condition is density independent and determined only by the ratio of inter- and intra-species interaction strength. Recently, Nadion and Petrov proposed that [<ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://doi.org/10.1103/PhysRevLett.126.115301"><i>Phys. Rev. Lett.</i> <b>126</b> 115301</ext-link>], in the vicinity of the mixing-demixing threshold, quantum fluctuations play an important role to affect the equilibrium stability, and as a result, the partially miscible state emerges. This new phase of quantum matter opens up new perspectives to explore the beyond mean-field effect in ultracold atomic gases.</sec><sec>In this work, according to the equation of state taking the Lee-Huang-Yang correction into consideration, we investigate the ground state phase diagram of repulsive binary Bose mixtures in the interacting regime suffering a weak mean-field instability. Under the thermodynamic balance conditions, the phase boundaries between the immiscible state, partially miscible state and the homogenous state are determined. For the equal-mass case, these phase transitions only take place on condition that intra-species interactions are in an asymmetric form. In terms of interaction parameters, we explicitly derive analytical expressions of the phase boundaries, which are appropriate to describe the transitions in sufficiently dilute atomic gases. At the quantum critical point, where the partially miscible state terminates, the susceptibility tensor of the density response exhibits a divergent behavior. For the unequal-mass case, the beyond-mean-field equation of state cannot be written in a compact form, thus the determination of the phase boundaries is more involved. By expanding the Lee-Huang-Yang energy expression to the terms linear in the concentration of the minority species, we analytically obtain the threshold density for the partially miscible transition. We also propose a discriminant function, from which the configuration of the partially miscible state can be identified for the given mass ratio and interaction strength. Applications of these theoretical results to experimental systems, such as sodium, potassium, and rubidium gases, are presented.</sec>

Double-degenerate Fermi mixtures of Li6 and Cr53 atoms

We report on the realization of a novel degenerate mixture of ultracold fermionic lithium and chromium atoms. Based on an all-optical approach, with an overall duty-cycle of about 13 seconds, we produce large and degenerate samples of more than 2$\times 10^5$ $^6$Li atoms and $10^5$ $^{53}$Cr atoms, with both species exhibiting normalized temperatures of about $T/T_{F}$=0.25. Additionally, through the exploitation of a crossed bichromatic optical dipole trap, we can controllably vary the density and degree of degeneracy of the two components almost independently, and widely tune the lithium-to-chromium density ratio. Our $^{6}$Li-$^{53}$Cr Fermi mixture opens the way to the investigation of a variety of exotic few- and many-body regimes of quantum matter, and it appears as an optimally-suited system to realize ultracold paramagnetic polar molecules, characterized by both electric and magnetic dipole moments. Ultimately, our strategy also provides an efficient pathway to produce dipolar Fermi gases, or spin-mixtures, of ultracold $^{53}$Cr atoms.

Interaction-controlled impurity transport in trapped mixtures of ultracold bosons

We explore the dynamical transport of an impurity between different embedding majority species which are spatially separated in a double well. The transfer and storage of the impurity is triggered by dynamically changing the interaction strengths between the impurity and the two majority species. We find a simple but efficient protocol consisting of linear ramps of majority-impurity interactions at designated times to pin or unpin the impurity. Our study of this highly imbalanced few-body triple mixture is conducted with the multi-layer multi-configuration time-dependent Hartree method for atomic mixtures which accounts for all interaction-induced correlations. We analyze the dynamics in terms of single-particle densities, entanglement growth and provide an effective potential description involving mean-fields of the interacting components. The majority components remain self-trapped in their individual wells at all times, which is a crucial element for the effectiveness of our protocol. During storage times each component performs low-amplitude dipole oscillations in a single well. Unexpectedly, the inter-species correlations possess a stabilizing impact on the transport and storage properties of the impurity particle.

Weber number and the outcome of binary collisions between quantum droplets

A theoretical analysis of binary collisions of quantum droplets under feasible experimental conditions is reported. Droplets formed from degenerate dilute Bose gases made up from binary mixtures of ultracold atoms are considered. Reliable expressions for the surface tension of the droplets are introduced based on a study of low energy excitations of their ground state within the random phase approximation. Their relevance is evaluated considering an estimation of the expected excitation energy having in mind the Thouless variational theorem. The surface tension expressions allow calculating the Weber number of the droplets involved in the collisions. Several regimes on the outcomes of the binary frontal collisions that range from the coalescence of the quantum droplets to their disintegration into smaller droplets are identified. Atoms losses of the droplets derived from self-evaporation and three-body scattering are quantified for both homo- and hetero-nuclear mixtures. Their control is mandatory for the observation of some interesting effects arising from droplets collisions.

Observation of magnetic Feshbach resonances between Cs and Yb173

We report the observation of magnetic Feshbach resonances between $^{173}\mathrm{Yb}$ and $^{133}\mathrm{Cs}$. In a mixture of Cs atoms prepared in the $(f=3,{m}_{f}=3)$ state and unpolarized fermionic $^{173}\mathrm{Yb}$, we observe resonant atom loss due to two sets of magnetic Feshbach resonances around 622 and 702 G. Resonances for individual Yb nuclear spin components ${m}_{i,\mathrm{Yb}}$ are split by its interaction with the Cs electronic spin, which also provides the main coupling mechanism for the observed resonances. The observed splittings and relative resonance strengths are in good agreement with theoretical predictions from coupled-channel calculations.

Classical route to ergodicity and scarring phenomena in a two-component Bose-Josephson junction

We consider a Bose-Josephson junction (BJJ) formed by a binary mixture of ultracold atoms to investigate the manifestation of coherent collective dynamics on ergodicity and quantum scars, unfolding the connection between them. By tuning the inter- and intra-species interaction, we demonstrate a rich variety of Josephson dynamics and transitions between them, which plays a crucial role in controlling the overall ergodic behavior. The signature of underlying classicality is revealed from the entanglement spectrum, which also elucidates the formation of quantum scars of unstable steady states and of periodic orbits leading to athermal behavior. The degree of ergodicity across the energy band and scarring phenomena can be probed from the auto-correlation function as well from the phase fluctuation of the condensates, which has relevance in cold atom experiments.

Quantized topological pumping of solitons in nonlinear photonics and ultracold atomic mixtures

Exploring the interplay between topological band structures and tunable nonlinearities has become possible with the development of synthetic lattice systems. In this emerging field of nonlinear topological physics, an experiment revealed the quantized motion of solitons in Thouless pumps and suggested that this phenomenon was dictated by the Chern number of the band from which solitons emanate. Here, we elucidate the origin of this nonlinear topological effect, by showing that the motion of solitons is established by the quantized displacement of the underlying Wannier functions. Our general theoretical approach, which fully clarifies the central role of the Chern number in solitonic pumps, provides a framework for describing the topological transport of nonlinear excitations in a broad class of physical systems. Exploiting this interdisciplinarity, we introduce an interaction-induced topological pump for ultracold atomic mixtures, where solitons of impurity atoms experience a quantized drift resulting from genuine interaction processes with their environment.

Optimal experiment design for element specific atom counting using multiple annular dark field scanning transmission electron microscopy detectors

This paper investigates the possible benefits for counting atoms of different chemical nature when analysing multiple 2D scanning transmission electron microscopy (STEM) images resulting from independent annular dark field (ADF) detector regimes. To reach this goal, the principles of statistical detection theory are used to quantify the probability of error when determining the number of atoms in atomic columns consisting of multiple types of elements. In order to apply this theory, atom-counting is formulated as a statistical hypothesis test, where each hypothesis corresponds to a specific number of atoms of each atom type in an atomic column. The probability of error, which is limited by the unavoidable presence of electron counting noise, can then be computed from scattering-cross sections extracted from multiple ADF STEM images. Minimisation of the probability of error as a function of the inner and outer angles of a specified number of independent ADF collection regimes results in optimal experimental designs. Based on simulations of spherical Au@Ag and Au@Pt core–shell nanoparticles, we investigate how the combination of two non-overlapping detector regimes helps to improve the probability of error when unscrambling two types of atoms. In particular, the combination of a narrow low angle ADF detector with a detector formed by the remaining annular collection regime is found to be optimal. The benefit is more significant if the atomic number Z difference becomes larger. In addition, we show the benefit of subdividing the detector regime into three collection areas for heterogeneous nanostructures based on a structure consisting of three types of elements, e.g., a mixture of Au, Ag and Al atoms. Finally, these results are compared with the probability of error resulting when one would ultimately use a pixelated 4D STEM detector and how this could help to further reduce the incident electron dose.

Tuning Long-Range Fermion-Mediated Interactions in Cold-Atom Quantum Simulators.

Engineering long-range interactions in cold-atom quantum simulators can lead to exotic quantum many-body behavior. Fermionic atoms in ultracold atomic mixtures can act as mediators, giving rise to long-range Ruderman-Kittel-Kasuya-Yosida-type interactions characterized by the dimensionality and density of the fermionic gas. Here, we propose several tuning knobs, accessible in current experimental platforms, that allow one to further control the range and shape of the mediated interactions, extending the existing quantum simulation toolbox. In particular, we include an additional optical lattice for the fermionic mediator, as well as anisotropic traps to change its dimensionality in a continuous manner. This allows us to interpolate between power-law and exponential decays, introducing an effective cutoff for the interaction range, as well as to tune the relative interaction strengths at different distances. Finally, we show how our approach allows one to investigate frustrated regimes that were not previously accessible, where symmetry-protected topological phases as well as chiral spin liquids emerge.

Investigation of Combinatorial WO3-MoO3 Mixed Layers by Spectroscopic Ellipsometry Using Different Optical Models.

Reactive (Ar-O2 plasma) magnetron sputtered WO3-MoO3 (nanometer scaled) mixed layers were investigated and mapped by Spectroscopic Ellipsometry (SE). The W- and Mo-targets were placed separately, and 30 × 30 cm glass substrates were slowly moved under the two (W and Mo) separated targets. We used different (oscillator- and Effective Medium Approximation, EMA-based) optical models to obtain the thickness and composition maps of the sample layer relatively quickly and in a cost-effective and contactless way. In addition, we used Rutherford Backscattering Spectrometry to check the SE results. Herein, we compare the “goodness” of different optical models depending upon the sample preparation conditions, for instance, the speed and cycle number of the substrate motion. Finally, we can choose between appropriate optical models (2-Tauc-Lorentz oscillator model vs. the Bruggeman Effective Medium Approximation, BEMA) depending on the process parameters. If one has more than one “molecular layer” in the “sublayers”, BEMA can be used. If one has an atomic mixture, the multiple oscillator model is better (more precise) for this type of layer structure.