Atomic Vapor Research Articles

Tailoring Sub‐Doppler Spectra of Thermal Atoms with a Dielectric Optical Metasurface Chip

AbstractCompact and robust structures to precisely control and acquire atomic spectra are increasingly important for the pursuit of widespread applications. Sub‐Doppler responses of thermal atoms are critical in constructing high‐precision devices and systems. In this study, a nanograting metasurface specifically is designed for atomic rubidium vapor and integrated it into a miniature vapor cell. Using the metasurface with built‐in multifunctional controls for light, pump‐probe atomic spectroscopy is established and sub‐Doppler responses are experimentally observed at low incident power. Moreover, the sub‐Doppler lineshape can be tailored by varying the incident polarization state. The spectrum transformation from absorption to transparency is observed. Using one of the sharp responses, laser stabilization with a stability of at 2 s can be achieved. This work reveals the effective control of atomic spectra with optical metasurface chips, which may have great potential for future developments in fundamental optics and novel optical applications.

Optimized optical tomography of quantum states of a room-temperature alkali-metal vapor

We demonstrate an experimental technique for the quantum-state tomography of the collective qutrit states of a room-temperature alkali-metal vapor. It is based on the measurements of the polarization of light traversing the vapor subjected to a magnetic field. To assess the technique's robustness against errors, experimental investigations are supported with numerical simulations. This not only allows us to determine the fidelity of the reconstructed states, but also to analyze the quality of the reconstruction for specific experimental parameters, such as light tuning and the number of measurements. By utilizing the conditional number, we demonstrate that the reconstruction robustness can be optimized by a proper adjustment of experimental parameters, and further improvement is possible with the repetition of specific measurements. Our results demonstrate the potential of this high-fidelity reconstruction method of quantum states of room-temperature atomic vapors. Published by the American Physical Society 2024

Three-dimensional modeling of multi-component vacuum arc considering anode vapor in actual magnetic field

For vacuum circuit breakers, the anode will change to active mode when the current is high enough. The vapor produced by the anode will become another important source of plasma. In this paper, a three-dimensional (3D) magnetohydrodynamic model considering anode vapor and multiple components is developed to study the vacuum circuit breakers with cup-shaped CuCr contact. The characteristics of arc under the actual magnetic field with different anode temperature distribution and different cathode utilization are simulated. Moreover, the ionization and recombination processes between different kinds of components are considered. The simulation results show that the arc current concentrates toward the center. The current value is high between electrodes slots under the actual magnetic field, which significantly affects the arc characteristics. At the same time, higher anode temperatures will produce more neutral atom vapor area (NAVA). Current is concentrated outside NAVA due to the low conductivity of NAVA. As NAVA expands, the constriction of current on the outside is more severe. The simulation results in this paper are consistent with the experimental results.

Internal Ceramic Protective Coating of Hollow‐Core Fibers

To optimize the use of hollow‐core photonic crystal fibers (HC‐PCF), their cores are filled with an atomic gas for an ultra‐enhanced interaction with an incident laser beam in applications such as atomic vapor microcells. One challenge in these gas‐filled HC‐PCFs is to control the physiochemical interactions between the gas medium and the silica inner surface of the fiber core surround. In this work, thus, the processing of ceramic coatings on glass substrates by chemical solution deposition is focused on. Also, the successful implementation of an original coating procedure for a deposition inside hollow‐core fibers with complex microstructures is described. It is indeed possible to form a thin, dense, inorganic, and amorphous layer with a low thickness, low roughness, and high transparency. To obtain such a result, several parameters must be controlled, including the concentration of the solution, the technique and the deposition time, as well as the heat treatment undergone by the fiber. In particular, the selected aluminosilicate coatings, which are nonporous and present a 20–30 nm thickness, demonstrate a considerable improvement of the lifetime properties of the fibers filled with rubidium vapor, without modifying its original guiding properties.

Probing molecules in gas cells of subwavelength thickness with high frequency resolution

Miniaturizing and integrating atomic vapor cells is widely investigated for the purposes of fundamental measurements and technological applications such as quantum sensing. Extending such platforms to the realm of molecular physics is a fascinating prospect that paves the way for compact frequency metrology as well as for exploring light-matter interactions with complex quantum objects. Here, we perform molecular rovibrational spectroscopy in a thin-cell of micrometric thickness, comparable to excitation wavelengths. We operate the cell in two distinct regions of the electromagnetic spectrum, probing ν1 + ν3 resonances of acetylene at 1.530 µm, within the telecommunications wavelength range, as well as the ν3 and ν2 resonances of SF6 and NH3 respectively, in the mid-infrared fingerprint region around 10.55 µm. Thin-cell confinement allows linear sub-Doppler transmission spectroscopy due to the coherent Dicke narrowing effect, here demonstrated for molecular rovibrations. Our experiment can find applications extending to the fields of compact molecular frequency references, atmospheric physics or fundamental precision measurements.

High angular momentum coupling for enhanced Rydberg-atom sensing in the very-high frequency band

Recent advances in Rydberg-atom electrometry detail promising applications in radio frequency communications. Presently, most applications use carrier frequencies greater than 1 GHz where resonant Autler–Townes splitting provides the highest sensitivity. This letter documents a series of experiments with Rydberg atomic sensors to collect and process waveforms from the automated identification system (AIS) used in maritime navigation in the very high frequency (VHF) band. Detection in this band is difficult with conventional resonant Autler–Townes based Rydberg sensing and requires a new approach. We show the results of a method called high angular momentum matching excited Raman (HAMMER), which enhances low frequency detection and exhibits superior sensitivity compared to the traditional AC Stark effect. From measurements of electromagnetically induced transparency in rubidium and cesium vapor cells, we show the relationship between incident electric field strength and observed signal-to-noise ratio and find that the sensitivity of the HAMMER scheme in rubidium achieved an equivalent single VHF tone sensitivity of 100μV/m/Hz. With these results, we estimate the usable range of the atomic vapor cell antenna for AIS waveforms given current technology and detection techniques.

Optical Extreme Learning Machines with Atomic Vapors

Extreme learning machines explore nonlinear random projections to perform computing tasks on high-dimensional output spaces. Since training only occurs at the output layer, the approach has the potential to speed up the training process and the capacity to turn any physical system into a computing platform. Yet, requiring strong nonlinear dynamics, optical solutions operating at fast processing rates and low power can be hard to achieve with conventional nonlinear optical materials. In this context, this manuscript explores the possibility of using atomic gases in near-resonant conditions to implement an optical extreme learning machine leveraging their enhanced nonlinear optical properties. Our results suggest that these systems have the potential not only to work as an optical extreme learning machine but also to perform these computations at the few-photon level, paving opportunities for energy-efficient computing solutions.

Effect of nanoclusters formed by metal impurity on magnesium vapor condensation in silicothermic process: a molecular dynamics study

In the silicothermic process, some metal oxide impurities that coexist with dolomite are inevitably reduced to metal vapors, which condense to metal impurities in the magnesium crystallizer. In this paper, the molecular dynamics simulation method was adopted to investigate the effect of impurity clusters on the crystallization transition of undercooled magnesium vapor. The results showed that saturated vapor atoms tend to nucleate on the pre-existing impurity cluster, promoting the crystallization rate of magnesium vapor. The promoting effects of impurity clusters on the crystallization of magnesium vapor depend on their sizes and species. The cluster with a larger size demonstrated a more substantial promoting impact. Moreover, in the three impurities studied in this paper, magnesium vapor condenses on the Fe cluster at the fastest rate due to the bcc structure of the Fe cluster and the strong interaction between Fe and Mg atoms. For Ni and Cu clusters with the same fcc structure, the promoting effect of the Ni cluster on the crystallization of Mg vapor is more evident because the interaction between Ni-Mg atoms is stronger than between Cu-Mg atoms.

Mercury content in commercial crustaceans of the Barents Sea

This study aims to identify the total mercury content in the muscle and hepatopancreas of the main commercial crustaceans from the Barents Sea.The material for this study was the samples of red king crab Paralithodes camtschaticus and northern shrimp Pandalus borealis caught during the research cruises conducted by “PINRO” from 2012 to 2022. This study examines the samples of muscle collected from crustaceans, as well as the samples of hepatopancreas collected from the red king crab.Novelty: This study involves abundant data that was used to make the first comparative analysis of the Hg concentration in red king crab and northern shrimp. A significant similarity in the levels of Hg content in the muscle of shrimp and crab at the mean level was shown. The paper provides maps of average Hg content in the studied species for the entire Barents Sea.Methods used: the total mercury content in the samples was estimated by flameless atomic absorption spectroscopy analysis using Shimadzu Cold Vapor Atomic Absorption Spectrophotometer (Japan). Statistical data processing and charting were done using MS Excel and application software package of Statistica 13.Results: The paper shows that the average concentration of Hg in the muscle and hepatopancreas of the studied hydrobionts did not exceed 0.2 mg/kg of wet weight that is the acceptable concentration established by sanitary standards. The content of Hg in the red king crab’ hepatopancreas was about 2 times higher than in the muscle. The paper makes an assumption on the species-specifity of Hg content in the red king crab’ muscle. The Hg content in the muscle of P. borealis is strongly related to its fattiness. The paper suggests calculated background levels of the total Hg concentration in the muscle of P. camtschaticus and P. borealis from the Barents Sea.Practical relevance: The results obtained were used to establish the safety compliance of commercial crustaceans with the requirements adopted in Russia.

Chirp asymmetry as an analogue of leptogenesis

The effective conjugation symmetry that arises in the rotating wave frame is the analogue of the charge conjugation symmetry in field theory. Breaking this effective conjugation symmetry leads to asymmetries between up-chirped and down-chirped excitation in quantum optical systems. We use semiclassical quantum optics theory to describe these processes and experimentally characterize the asymmetry in the optical response in chirped, two-color saturated absorption spectroscopy (SAS) in an atomic vapor cell. Doing so demonstrates a theoretical and phenomenological correspondence to the simplest model of leptogenesis, the process by which our universe purportedly went from equal amounts of matter and antimatter to its present matter excess. The understanding of the asymmetry as due to a broken discrete symmetry under chirp illuminates the underlying processes responsible for other chirp asymmetries previously noted in the literature.

Probing the interfacial structure of aqueous surfactants through helium atom evaporation.

Dissolved helium atoms evaporate from liquids in super-Maxwellian speed distributions because their interactions are too weak to enforce full thermal equilibration at the surface as they are "squeezed" out of solution. The excess speeds of these He atoms reflect their final interactions with solvent and solute molecules at the surfaces of water and other liquids. We extend this observation by monitoring He atom evaporation from salty water solutions coated with surfactants. These surface-active molecules span neutral, anionic, and cationic amphiphiles: butanol, 3-methyl-1-butanol, pentanol, pentanoic acid, pentanoate, tetrabutylammonium, benzyltrimethylammonium, hexyltrimethylammonium, and dodecyltrimethylammonium, each characterized by surface tension measurements. The helium energy distributions, recorded in vacuum using a salty water microjet, reveal a sharp distinction between neutral and ionic surfactant films. Helium atoms evaporate through neutral surfactant monolayers in speed distributions that are similar to a pure hydrocarbon, reflecting the common alkyl chains of both. In contrast, He atoms appear to evaporate through ionic surfactant layers in distributions that are closer to pure salty water. We speculate that the ionic surfactants distribute themselves more loosely and deeply through the top layers of the aqueous solution than do neutral surfactants, with gaps between the surfactants that may be filled with salty water. This difference is supported by prior molecular dynamics simulations and ion scattering measurements of surfactant solutions.

Applications of low-valent compounds with heavy group-14 elements.

Over the last two decades, the low-valent compounds of group-14 elements have received significant attention in several fields of chemistry owing to their unique electronic properties. The low-valent group-14 species include tetrylenes, tetryliumylidene, tetrylones, dimetallenes and dimetallynes. These low-valent group-14 species have shown applications in various areas such as organic transformations (hydroboration, cyanosilylation, N-functionalisation of amines, and hydroamination), small molecule activation (e.g. P4, As4, CO2, CO, H2, alkene, and alkyne) and materials. This review presents an in-depth discussion on low-valent group-14 species-catalyzed reactions, including polymerization of rac-lactide, L-lactide, DL-lactide, and caprolactone, followed by their photophysical properties (phosphorescence and fluorescence), thin film deposition (atomic layer deposition and vapor phase deposition), and medicinal applications. This review concisely summarizes current developments of low-valent heavier group-14 compounds, covering synthetic methodologies, structural aspects, and their applications in various fields of chemistry. Finally, their opportunities and challenges are examined and emphasized.

Measurement of the main neutral species densities and temperatures in iodine plasmas using optical absorption techniques

Iodine is a promising propellant for future plasma thrusters used in space propulsion. It is therefore important to understand the basic physics and chemistry of low-pressure iodine plasmas. In the present work, optical absorption methods are used to measure the densities of iodine molecules, I2, and iodine atoms, I, the translational temperature of the atoms and the dissociation fraction. The plasma is generated in a long quartz tube by a capacitively coupled RF discharge, and the pressure is varied between a few Pa and a few tens of Pa. The translational temperature of the atom vapour increases both with RF power and with pressure and reaches 1000 K at 50 W and 25 Pa. The molecules appear to be efficiently dissociated, with a dissociation fraction found above 65%, on average along the line-of-sight, at 120 W and 5 Pa. The population of the upper, 2P1/2∘ , fine-structure level of the atomic ground term is found to be negligible, which confirms the existence of a high quenching rate, due to collisions with molecules and/or atoms. These measurements can be helpful for chemistry models of iodine plasmas.

Ion-collection characteristics of photoplasma for atomic vapor laser isotope separator module in electrostatic fields

The laser-based isotope separation process is currently pursued to enrich precursor medical isotopes like lutetium-176 and ytterbium-176. India has successfully produced radionuclide lutetium-177 for clinical use by neutron activation. Atomic vapor laser isotope separation (AVLIS) is used as the enrichment technology. Understanding the physics and technology of processes, like atomic-beam generation, photoplasma production, and ion collection, is essential to designing any AVLIS module. So, a stand-alone research facility was developed before the production plant. This article describes the facility and the experimental and theoretical studies of ion collection in electrostatic fields using barium as the working element. Two types of ion extractors, plate–photoplasma–plate and plate–photoplasma–grid–plate, were designed and fabricated. A model of photo-ion collection in these electrostatic ion extractors was arrived at. Scaling of the initial photo-ion densities and the electric fields is crucial to photoplasma evolution spanning single-particle to collective regimes. Estimates of ion-collection rates of the Indian AVLIS modules for lutetium-176 and ytterbium-176 were carried out. By invoking plasma physics, the technological aspect of producing enriched isotopes was solved by judiciously integrating the atom source, laser system, photoplasma, and ion-extractor geometries. Limitations of the electrostatic ion extractors were also flagged.

Efficient Loading of an Atom Chip from a Low-Velocity Atomic Beam

Various regimes of the loading of a magneto-optical trap formed near an atom chip, such as loading from thermal atomic vapors and from a low-velocity atomic beam, have been studied on an example of 87Rb atoms. The possibility of controlling the loading of the magneto-optical trap by spatially controlling the atomic beam has been demonstrated. This has made it possible to increase the loading rate of atoms into the magneto-optical trap with keeping ultrahigh vacuum near the atom chip. The maximum number of atoms in the magneto-optical trap at optimal loading regimes is 4.9 × 107. In this case, the measured lifetime of atoms in the magneto-optical trap is 4.1 s.

Лабораторная работа «Изучение многофотонной ионизации в условиях резонансного возбуждения атомарных паров»

The developed laboratory work is described, designed to study multiphoton ionization under conditions of resonant excitation of atomic vapors by frequency-tunable laser radiation. Atomic pairs of potassium and rubidium were chosen as objects of study. To demonstrate the resonant nature of multiphoton ionization, the results of studies of the dependence of the magnitude of the ion signal on the frequency of laser radiation causing this signal are presented. Analytical expressions are given to describe the experimentally observed patterns of resonant ionization processes. Laboratory work is part of a set of works on the study of resonant nonlinear optics for students studying physics at universities.

Research on intensity–difference squeezing enhancement of phase-sensitive amplifier based on coherent feedback

The intensity-difference squeezed state is an important concept in quantum optics, which is not only of great significance for fundamental research in quantum physics, but also an important quantum resource in the fields of quantum communication, quantum computing, and quantum precision measurement. The optical parametric amplifier based on atomic four-wave mixing is one of the most effective means to achieve intensity-difference squeezed light. However, due to the absorption loss of atomic vapor in the light field, the output squeezing still needs improving. By feeding the non-classical optical field from the optical parametric amplifier back to the input port, the quantum characteristics of its output optical field can be enhanced. However, the intensity-difference squeezing enhancement from a phase-insensitive amplifier is experimentally realized based on coherent feedback control. The intensity-difference squeezing enhancement of the phase-sensitive amplifier has not been discussed. In this work, a two-port coherent feedback-controlled phase-sensitive amplifier is analyzed theoretically. The dependence of the intensity-difference squeezing, respectively, on the feedback intensity, the intensity gain of the optical parametric amplifier, and the losses of the system are investigated. For the ideal case in which the losses of the system are ignored, infinite squeezing can be achieved by adjusting the strength and phase of feedback. Considering the actual atomic absorption losses, squeezing enhancement can also be achieved over a wide range of intensity gains within a certain feedback intensity range. In addition, the squeezing enhancement is quite efficient for the medium intensity gain range. The intensity-difference squeezing enhancement strongly depends on the absorption loss of atomic vapor. The smaller the absorption loss, the more significant the squeezing enhancement effect is. Furthermore, the experimental feasibility of this scheme is also considered in detail. Our research can provide useful references for achieving high-quality non classical light fields in experiment, which may find applications in quantum information processing and quantum precise measurement.

Research on combustion process optimization of marine diesel engines based on dual-injector system

Marine diesel engines are widely used with their strong power and mature technology. However, in recent years, the emphasis on environmental protection has made combustion pollutants the focus of attention, and the new regulations of the International Maritime Organization (IMO) and various countries have put forward new requirements and challenges for diesel engine combustion and emission performance. Due to the large size and large amount of circulating fuel injection, the incomplete mixing of fuel in the cylinder and the local violent combustion of high-power medium-speed marine diesel engines are important reasons for low thermal efficiency and high pollutant emissions. To achieve efficient and clean combustion of fuel in the cylinder, a dual-injector combustion system is designed on a dual-fuel engine basis, aiming to add a micro-injection before the central injection and provide positive in-cylinder flow and hot atmosphere for the atomized combustion of the central-injection fuel, so that the combustion in the cylinder is reasonably arranged, the thermal efficiency is improved and NOx emissions are reduced. The 3D simulation model was established by CFD software CONVERGE, and the physical model was calibrated according to the data of the pure diesel mode of the dual-fuel engine, and the influence of the small pilot-injection fuel volume on the development of spray and combustion in the cylinder at high and low load was analyzed. It was found that the small pilot-injection fuel volume at a high load had little effect on the atomization evaporation of the main-injection fuel and the hot atmosphere in the cylinder, so the improvement effect of combustion quality was not obvious, while the pilot-injection volume with the same pilot-injection capacity as high load relatively accounted for a large proportion at the low load with a small cycle injection volume. Without changing the injector specification settings of the original dual-fuel engine, the thermal efficiency was increased by 6.13% and the NOx generation was reduced by 22.42% by optimizing the injection timing, injection duration, and injection amount.

Continuous broadband microwave electric field measurement in Rydberg atoms based on the DC Stark effect

We demonstrate a method for broadband tunable continuous frequency electric field measurement based on the DC Stark effect in Rydberg atoms. In our experiment, we place a pair of parallel electrode plates inside the atomic vapor cell, utilizing the DC Stark effect to induce splitting and shifting of the Rydberg energy levels, thereby altering the resonance frequency of the Stark subpeaks. By employing the 52D5/2 Rydberg state, we achieve electric field measurements in the frequency range of 5.083–14.470 GHz. At an EDC of 3.45 V/cm and a resonant microwave frequency of 14.470 GHz, using heterodyne technology, the microwave electric field sensitivity is 538.89 μV/cm/√Hz, with a linear dynamic range of 23 dB. In comparison, a Rydberg heterodyne receiver with an EDC of 0 V/cm and a resonant microwave frequency of 5.083 GHz has a sensitivity of 5.43 μV/cm/√Hz and a linear dynamic range of 51 dB. This work will promote the study of atomic microwave receivers in continuous microwave frequency measurement.

Morphological and Electrical Characterization of AlGaN/GaN Heterostructures Modified By Atomic Layer Etching

Modern microelectronic components for high-power and high-frequency applications based on III-V compound semiconductors offer high break down voltage (GaN: 5 MV/cm and AlN: 15 MV/cm) at low specific on-resistance. However, it requires reliability and reproducibility of the production processes. Going to higher frequencies (5 GHz and beyond) and more integration in consumer electronics, smaller structure sizes are needed. This is going along with increasing demands on the manufacturing processes like dry etching. The main goal is to reach smaller and high controllable etching rates, going down to single atomic layers, low damage, and minimized surface roughness. Atomic layer etching (ALE) represents a key technology in order to achieve such requirements.An ALE process consists of two independent steps forming a repeatable cycle with a specific etching amount per cycle (EPC). First a surface modification is done by a chemical precursor i.e., adsorbing or oxidizing the surface. The second step is the removal of the modified layer, either physically by low energy non-reactive ion bombardment (Plasma Enhanced ALE [PEALE]) or chemically by a reactive species (Thermal ALE). The two steps are separated by an inert gas purge. This purging grants the removal of the chemistry after the first step, preventing further chemical reaction and transporting the chemical products out of the chamber after the second step.In this study, a PEALE conducted on different tools is used, for gate and contact recess study in a AlGaN/GaN heterostructure to form high electron mobility transistors (HEMT) with reduced ohmic contact resistance and threshold voltages. The results show a reduction of ohmic contact resistance at reduced forming temperatures and a linear dependence of the threshold voltage on gate recess depth. In order to determine the etching rate and roughness, atomic force microscopy (AFM) measurements were performed.The PEALE module is either integrated into a cluster tool consisting of atomic layer deposition (ALD) and chemical vapor deposition (CVD) or done in a combined ALD/ALE chamber. This opens the possibility of etching and depositing in-situ, reducing contamination and degradation of the substrate material.By this means, metal insulator semiconductor (MIS)-HEMTS with a recessed gate are studied. The monitoring of the individual processes is achieved by test structures like transfer length method structures (TLM) and metal oxide semiconductor (MOS), which showed the improved electric performance of these devices and may indicate unwanted interface issues, respectively. Additional, pre- and post-treatments could improve the interfaces further. The results will be presented and discussed in terms of ALE process development and optimization.This work was financially supported within the ALEStar project by the government of the Free-state of Saxony and the European Regional Development Fund under grant no. SAB 100402929.