Surface Of Helium Research Articles

Kinetics of electrohydrodynamic instability of a charged liquid helium surface

Kinetics of electrohydrodynamic instability of a charged liquid helium surface

Coulomb Interaction-Driven Entanglement of Electrons on Helium

The generation and evolution of entanglement in many-body systems is an active area of research that spans multiple fields, from quantum information science to the simulation of quantum many-body systems encountered in condensed matter, subatomic physics, and quantum chemistry. Motivated by recent experiments exploring quantum information processing systems with electrons trapped above the surface of cryogenic noble gas substrates, we theoretically investigate the generation of entanglement between two electrons via their unscreened Coulomb interaction. The model system consists of two electrons confined in separate electrostatic traps that establish microwave-frequency quantized states of their motion. We compute the motional energy spectra of the electrons, as well as their entanglement, by diagonalizing the model Hamiltonian with respect to a single-particle Hartree product basis. We also compare our results with the predictions of an effective Hamiltonian. The computational procedure outlined here can be employed for device design and guidance of experimental implementations. In particular, the theoretical tools developed here can be used for fine-tuning and optimization of control parameters in future experiments with electrons trapped above the surface of superfluid helium or solid neon. Published by the American Physical Society 2024

Biochar data into structure: A methodology for generating large-scale atomistic representations

A well-defined methodology for constructing appropriate atomistic representations of biochar will aid in visualizing the structural features and elucidating biochar behavior with molecular dynamics (MD) simulations. Such knowledge will facilitate engineering biochars tailored to specific applications. To achieve this goal, we adapted modeling strategies applied in coal science by employing multi-cross-polarization 13C nuclear magnetic resonance, ultimate analysis, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy to identify functional groups. Helium density, surface area, and porosity were used to assess structural features. Biochar's aromatic cluster size distribution was proposed based on data from the benzene polycarboxylic acid method. The computational framework reduces bias by incorporating chemical information derived from density functional theory, reactive MD simulations, and advanced characterization data. The construction approach was successfully applied to cellulose biochars produced at four temperatures, obtaining independent representations with a relative error on the atomic contents of <10 % for oxygen and nitrogen and <5 % for carbon and hydrogen. The atomistic representations were validated using X-ray diffraction, electron spin resonance data, and laser desorption/ionization Fourier-transform ion cyclotron resonance-mass spectrometry. The code will assist others in overcoming structural creation barriers and enable the utilization of the generated structures for further simulations.

Helium aggregation and surface morphology near grain boundaries in plasma-facing tungsten

We conduct molecular dynamics simulations of helium in tungsten to study the interaction of helium with grain boundaries. Model systems with grain boundary planes perpendicular to the surface and parallel to the surface are considered. The net attraction of mobile helium to the grain boundary results in a “depleted region” within approximately 3.5 nm of the grain boundary plane at low fluence, and once on the plane of the grain boundary, helium transport slows considerably. Helium retention is also strongly affected by the grain boundaries and their density: grain boundary planes approximately 6 nm beneath the plasma-facing surface and parallel to the surface tend to reduce the maximum bubble size due to the attraction of mobile clusters to the grain boundary plane, which lowers the concentration of helium near the surface (where it is being implanted); grain boundaries perpendicular to the surface tend to increase retention due to retention on the grain boundary plane. For grain boundaries parallel to the surface, the strong gettering effect of the grain boundaries on helium results in essentially no helium penetration through the grain boundary during the first 1.5 μs of plasma exposure at a flux of 1.6×1025 m−2s−1, corresponding to fluences on the order of 1020 m−2. Coarse-grained simulations capable of capturing the long-term dynamics of helium aggregation near grain boundaries would be required to determine whether these effects would have any measurable impact on phenomena, such as tungsten fuzz growth.

Quantum computing using floating electrons on cryogenic substrates: Potential and challenges

In this review, we introduce a developing qubit platform: floating-electron-based qubits. Electrons floating in a vacuum above the surface of liquid helium or solid neon emerge as promising candidates for qubits, especially due to their expected long coherence times. Despite being in the early stages, a variety of recent experiments from different groups have shown substantial potential in this role. We survey a range of theoretical proposals and recent experiments, primarily focusing on the use of the spin state as the qubit state, wherein the spin and charge states are hybridized. Throughout these proposals and experiments, the charge state is coupled to an LC resonator, which facilitates both the control and readout mechanisms for the spin state via an artificially introduced spin–charge coupling.

The dynamics of the interfacial surface of helium II–vapor in a U-shaped channel

The dynamics of the interfacial surface of helium II–vapor in a U-shaped channel

Two-dimensional Brownian motion of active particle on superfluid helium surface

We report an experimental study of the 2D dynamics of active particles driven by quantum vortices on the free surface of superfluid helium at T = 1.45 К. The particle motion at short times (< 25 ms) relates to anomalous diffusion mode typical for active particles, while for longer times it corresponds to normal diffusion mode. The values of the rotational and translational kinetic energies of the particle allow to determine for the first time the intensity of the particle-vortex interaction and the dissipation rate of the vortex bundle energy. Strong bonding between a particle and a vortex is explained by coupling of normal and superfluid components.

Generation of Quantum Vortices by Waves on the Surface of Superfluid Helium

The formation of quantum vortices by two mutually perpendicular waves excited on the surface of superfluid helium has been observed. The interaction of negative charges injected under the surface of He-II with the vortex flow of the liquid, which is formed by surface waves at frequencies from 20 to 49.9 Hz, in the temperature range of 1.5–2.17 K has been studied experimentally by analyzing the current distribution detected by vertically oriented segments of a receiving collector. The efficient capture of injected charges by quantum vortices has been observed at a temperature ofT= 1.5 K, which leads to a significant redistribution of currents between segments of the receiving collector. Charges leave traps on quantum vortices at temperatures nearT= 1.7 K. With a further increase in the temperature, injected charges are scattered on vortex flows of the normal component, which are generated by surface waves.

Surface chemical composition of single WNh stars

Context. Wolf–Rayet (WR) stars of the WNh category contain a significant fraction of hydrogen at their surface. They can be hydrogen-burning, very massive stars or stars in a post-main sequence phase of evolution. Also, WNh stars are sometimes not included in population synthesis models. Aims. We aim to better characterise the properties of single WNh stars in the Galaxy and the Magellanic Clouds. In particular, we want to constrain their surface chemistry beyond the hydrogen content by determining the helium, carbon, and nitrogen surface abundances. Methods. We perform a spectroscopic analysis of 22 single WNh stars. We fit their ultraviolet and/or optical spectra using synthetic spectra computed with the code CMFGEN. We determine the main stellar parameters (temperature, luminosity, mass-loss rates) and the surface H, He, C, and N mass fractions. We investigate the ability of current evolutionary models to reproduce all parameters at the same time. Results. We find that all WNh stars show the signatures of CNO-cycle material at their surface: they are carbon-depleted and nitrogen-rich. A clear trend of higher nitrogen content at higher metallicity is observed, as expected. The amount of hydrogen (X) varies significantly from one star to another, independently of luminosity. Values of X larger than 0.4 are not exceptional. The majority of Galactic WNh stars can be explained by evolutionary models, provided sufficient fine-tuning of the input parameters of evolutionary calculations. At lower metallicity, most stars escape predictions from evolutionary models. This has been noted in the literature but constraints on the surface nitrogen content exacerbate this severe issue. Conclusions. Our study highlights the need to refine the treatment of WR stars in both stellar evolution and population synthesis models.

Realizations, Characterizations, and Manipulations of Two-Dimensional Electron Systems Floating above Superfluid Helium Surfaces

Electron systems in low dimensions are enriched with many superior properties for both fundamental research and technical developments. Wide tunability of electron density, high mobility of motion, and feasible controllability in microscales are the most prominent advantages that researchers strive for. Nevertheless, it is always difficult to fulfill all in one solid-state system. Two-dimensional electron systems (2DESs) floating above the superfluid helium surfaces are thought to meet these three requirements simultaneously, ensured by the atomic smoothness of surfaces and the electric neutrality of helium. Here we report our recent work in preparing, characterizing, and manipulating 2DESs on superfluid helium. We realized a tunability of electron density over one order of magnitude and tuned their transport properties by varying electron distribution and measurement frequency. The work we engage in is crucial for advancing research in many-body physics and for development of single-electron quantum devices rooted in these electron systems.

Generation of Quantum Vortices by Waves on the Surface of Superfluid Helium

The formation of quantum vortices by two mutually perpendicular waves excited on the surface of superfluid helium has been observed. The interaction of negative charges injected under the surface of He-II with the vortex flow of the liquid, which is formed by surface waves at frequencies from 20 to 49.9 Hz, in the temperature range of 1.5–2.17 K has been studied experimentally by analyzing the current distribution detected by vertically oriented segments of a receiving collector. The efficient capture of injected charges by quantum vortices has been observed at a temperature of T = 1.5 K, which leads to a significant redistribution of currents between segments of the receiving collector. Charges leave traps on quantum vortices at temperatures near T = 1.7 K. With a further increase in the temperature, injected charges are scattered on vortex flows of the normal component, which are generated by surface waves.

Anomalous temperature dependence of energy levels of electrons on helium

We report on magnetoconductivity measurements of electrons on helium exposed to resonant microwave irradiation within the temperature range associated with electron-ripplon scattering. Our findings reveal a non-monotonic temperature dependence of the intersubband frequency, with an abrupt decrease observed at temperatures below 0.3 K. We attribute this unexpected energy levels shift to the adsorption of 3He impurities near the liquid helium surface at low temperatures and such behavior is consistent with recent theoretical calculations of the surface electron energy spectra on 3He–4He mixtures.

What surfaces in the operation of noble liquids dark matter detectors

Though noble element dual-phase detectors have a long application history in dark matter searches, some uncertainties and differences in backgrounds persist. We compare effects caused by unextracted electrons on the liquid-gas interface in Xe and Ar dual-phase detectors with a large family of phenomena at the liquid helium surface. We pose that electron and ion accumulation on the liquid surface in detectors can lead to the formation of ordered surface states, charged liquid surface instabilities in an electric field, electrospraying, interactions with surface waves, and other effects. Not only delayed electron emission signals can be generated, but the extraction efficiency for electrons produced below the liquid surface can be altered by the presence of surface charges. Several factors lead to surface electron accumulation, and problems can become more severe with the increased detector size. We discuss possible experiments to reveal surface electron effects and design changes to alleviate electron accumulation. We conclude that studies of these effects are desirable before making final design decisions for the new multi-ton liquid Xe dark matter detector projects like DARWIN, XLZD, and large Ar dual-phase detectors.

Comparative analysis of helium and air surface micro-discharge plasma treatment on the microbial reduction and quality attributes of beef slices

This work aimed to compare the effects of helium and air surface micro-discharge (SMD) plasma on the microbial safety and quality of beef tissues. For the beef tissue model, the concentration and diffusion depth of hydroxyl radical and ozone have different change patterns over plasma treatment time and distance in helium and air SMD plasma. The inactivation efficiency of helium plasma depended on the plasma treatment time and distance, while the inactivation efficiency of air plasma only depended on the treatment time. For the fresh beef slices, air SMD plasma treatment exhibited a higher antimicrobial activity against S. aureus and E. coli than helium SMD plasma treatment (1.5 versus 0.9; 0.9 versus 0.28 log CFU/g at 10 min). However, air SMD plasma treatment caused more adverse effects on beef quality, leading to a smooth surface, extensive lipid oxidation, protein structure damage, low pH and discoloration compared to helium SMD plasma treatment. This work provides valuable guidelines for the working gas choice in the practical application of plasma to meat decontamination.

Mechanisms of helium irradiation blistering and surface deformation in tungsten

Helium irradiation blistering in tungsten is of intense interest for plasma-facing materials under fusion-relevant conditions. Previous studies have revealed that the surface blistering is closely related to the evolution of subsurface microstructures (e.g., bubbles and cracks), but its dependence on the surface orientation and deformation remains unclear. The present work reports the helium irradiation blistering on the surface planes of tungsten {100}, {110} and {111}. A systematic study of helium irradiation blistering was conducted at room temperature by utilizing a Helium Ion Microscope. The cross-sectional microstructural analyses at different ion fluences confirmed that the blistering deformation starts with the nanocrack nucleation, initiated at the peak in the bubble depth distribution via interbubble fracture, and is followed by the gas buildup in a primary cavity. In addition, the comparison of blistering behaviors between 1-µm-diameter and 2-µm-diameter circular areas revealed that only the blisters formed on tungsten {100} can grow to a larger size, whereas those formed on tungsten {110} or {111} tend to become wrinkled or burst when the irradiated area increases. Combined with the micropillar compressions in a Scanning Electron Microscope, it was also found that the surface deformation is orientation-dependent and associated with the number, symmetry and distribution of effective slip systems in body-centered-cubic transition metals. Our findings provide new evidence and insights into the mechanisms of helium irradiation blistering and surface deformation in tungsten.

Multilayer nanoparticle-polymer metamaterial for radiative cooling of the stratospheric airship

This paper presents a promising solution to superheat of stratospheric airship with radiative cooling envelope, which has no change in pneumatic profile, structural weight, and power consumption. In this study, a multilayer nanoparticle-polymer metamaterial (MNPM) is hierarchically designed to provide reflectivity across visible wavelength and emissivity in atmospheric window. In this paper, the specimens and ball models are firstly fabricated, the cooling performances of which are tested for ground experiments. The temperatures of MNPM and silica/Ag specimens are 6.7 °C and 10.8 °C at noon in Tianjin. The inner gas and surface temperatures of MNPM scale ball are 11.7 °C and 14.6 °C, lower than silica/Ag by 4.5 °C and 4.6 °C, respectively. Subsequently, the flight experiments verify the cooling performance of MNPM, the maximum temperature of which is lower than the control group by 15.4 °C in stratosphere. Finally, the FLUENT simulations illustrate the cooling performance of stratospheric balloon and airship equipped with solar panel. The MNPM has a better cooling capacity for the internal helium and top surface throughout the day and a weak warming capacity for the bottom surface at night. Considering solar panels, the MNPM reduces the helium temperature by 8.1 °C, and the day-night superheat of the helium temperature is only 19.8 °C.

Visualization of oscillatory electron dynamics on the surface of liquid helium

We investigate the time traces of currents induced in five segmented electrodes by the motion of electrons on the surface of liquid $^{4}\mathrm{He}$ at $\ensuremath{\sim}0.3$ K, that are placed in a perpendicular magnetic field and exposed to microwave radiation. Nonlinear dynamics methods are utilized to explore the characteristic features of the current oscillations in the electrodes for different electron densities and pressing voltages. The wavelet phase coherence and phase shift are calculated to obtain the coherence relationships between the signals in all five electrodes as functions of the pressing voltage. Coupling analysis of the ridge-extracted instantaneous frequencies revealed the directions of motion of electrons inside the cell and provided evidence of strong phase coupling at a pressing voltage of 4.20 V. These classical methods reveal that the motion is oscillatory, with a varying frequency subject to a constant frequency modulation. High harmonics due to nonlinearity arise at higher frequencies where the resonance condition is satisfied at a pressing voltage of 4.20 V for low-electron density. Our approach provides a platform for investigating these phenomena analytically. We show that slow gravity waves on the helium surface modulate the electronic oscillatory behavior and illustrate that the model in fact produces three-dimensional dynamics. Motion of electrons on the surface of liquid helium is shown to be a paradigmatic example of a chronotaxic system, i.e., a system that undergoes continuous perturbation but is nonetheless capable of maintaining its stability.

Modeling tungsten response under helium plasma irradiation: a review

Tungsten, a leading candidate for plasma-facing materials (PFM) in future fusion devices, will be exposed to high-flux low-energy helium plasma under the anticipated fusion operation conditions. In the past two decades, experiments have revealed that exposure to helium plasma strongly modifies the surface morphology and hence the sputtering, thermal and other properties of tungsten, posing a serious danger to the performance and lifetime of tungsten and the steady-state operation of plasma. In this article, we provide a review of modeling and simulation efforts on the long-term evolution of helium bubbles, surface morphology, and property changes of tungsten exposed to low-energy helium plasma. The current gap and outstanding challenges to establish a predictive modeling capability for dynamic evolution of PFM are discussed.

Image-charge detection of the Rydberg transition of electrons on superfluid helium confined in a microchannel structure

The image-charge detection provides a new direct method for the detection of the Rydberg transition of electrons trapped on the surface of liquid helium. The interest in this method is motivated by the possibility to accomplish the spin state readout for a single trapped electron, thus opening a new pathway towards using electron spins on liquid helium for quantum computing. Here, we report on the image-charge detection of the Rydberg transition in a many-electron system confined in an array of 20 μm wide and 4 μm deep channels filled with superfluid helium. Such detection is made possible because of a significant enhancement of the image-charge signal due to close proximity of trapped electrons to the electrodes embedded in the microchannel structure. The transition frequency of electrons in the range of 400–500 GHz is highly controllable by the dc bias voltages applied to the device and is in a good agreement with our calculations. This work demonstrates that microchannel structures provide a suitable platform for electron manipulation and their quantum state detection, with a feasibility of scaling the detection method to a single electron.

Atomic diffusion and turbulent mixing in solar-like stars: Impact on the fundamental properties of FG-type stars

Context. Chemical composition is an important factor that affects stellar evolution. The element abundance on the stellar surface evolves along the lifetime of the star because of transport processes, including atomic diffusion. However, models of stars with masses higher than about 1.2 M⊙ predict unrealistic variations at the stellar surface. This indicates the need for competing transport processes that are mostly computationally expensive for large grids of stellar models. Aims. The purpose of this study is to implement turbulent mixing in stellar models and assess the possibility of reproducing the effect of radiative accelerations with turbulent mixing for elements like iron in order to make the computation of large grids possible. Methods. We computed stellar models with the Module for Experiments in Stellar Astrophysics code and assessed the effects of atomic diffusion (with radiative acceleration) in the presence of turbulent mixing. Starting from a turbulent mixing prescription already calibrated on helium surface abundances of F-type stars as a reference, we parametrised the effect of radiative accelerations on iron with a turbulent diffusion coefficient. Finally, we tested this parametrisation by modelling two F-type stars of the Kepler Legacy sample. Results. We found that, for iron, a parametrisation of turbulent mixing that simulates the effect of radiative acceleration is possible. This leads to an increase in the efficiency of the turbulent mixing to counteract the effect of gravitational settling. This approximation does not affect significantly the surface abundances of the other elements we studied, except for oxygen and calcium. We demonstrate that this parametrisation has a negligible impact on the accuracy of the seismic properties inferred with these models. Moreover, turbulent mixing makes the computation of realistic F-type star models including the effect atomic diffusion possible. This leads to differences of about 10% in the inferred ages compared to results obtained with models that neglect these processes. Conclusions. The inclusion of turbulent mixing and atomic diffusion with radiative accelerations allows a more realistic characterisation of F-type stars. The parametrisation of the effect of radiative acceleration on iron opens the possibility to compute larger grids of stellar models in a reasonable amount of time, which is currently difficult when the different chemical transport mechanisms, especially radiative accelerations, are considered, although this parametrisation cannot simulate the evolution of abundances of all elements (e.g. calcium).