Atomic Resonance Research Articles

Peptide-induced mycobacterial membrane permeabilization studies to enhance drug uptake.

Anti-tubercular therapy is a long-term process during which the chances of drug resistance are high due to its inaccurate distribution. The bioavailability of the drug is limited due to the pharmacokinetic parameters and cell membrane barriers. Rational designing of the drug is essential to validate the required entry into the target cell to eliminate chances of resistance. Australian frog peptides aurein1.2 and maculatin1.1 have membrane-active properties which could be exploited to enhance the drug uptake in Mycobacterium. This work used a combination of biophysical techniques to study the peptide interaction patterns on mycobacterial cell envelope layers. Atomic force microscopy and surface plasmon resonance studies revealed that aurein1.2 insertion leads to lipid removal in the mycobacterial inner membrane lipids. In contrast, maculatin1.1 insertion leads to the blebbing of the bilayer. Dye-leakage assay performed using confocal microscopy promises aurein1.2 to effectively permeabilize outer and inner mycobacterial membranes, while maculatin1.1 permeabilizes selectively. However, flow cytometry studies indicated greater permeabilization of propidium iodide into the intact Mycobacterium smegmatis when treated with maculatin1.1, indicating the formation of a larger surface area of blebbing compared to the area of lipid removal by aurein1.2. When used in combination with anti-tubercular drugs smaller than the pores formed by the peptides, these molecules can spur up the drug uptake to enhance intracellular drug concentrations. Leveraging the membrane-drug interaction profiles unique to mycobacteria, specific chemotypes consisting of outer membrane-disruptive agents and anti-tubercular drugs may provide strategies for new combinational TB therapies.

QCM‐D Study of the Formation of Solid‐Supported Artificial Lipid Membranes: State‐of‐the‐Art, Recent Advances, and Perspectives

Solid‐supported lipid bilayers (SLBs) are excellent platforms for studying the biophysical properties of cell membranes. Among the existing approaches used to form SLBs, vesicle fusion and rupture onto solid supports are most commonly employed owing to their straightforward procedure. The current understanding of the mechanisms behind this approach has greatly benefited from the use of surface‐sensitive techniques, especially quartz crystal microbalance with dissipation monitoring (QCM‐D) in combination with other analytical techniques, such as atomic force microscopy (AFM) or localized surface plasmon resonance (LSPR). Herein, an overview of the pathways of vesicle adsorption and rupture under various experimental conditions is provided. Examples including recent findings of how the variation of the properties of lipid vesicles (size, charge), aqueous buffer (pH, ionic strength, osmotic pressure), and solid support (surface energy) affect the pathway mechanism of adsorption and rupture are provided. Recent reports on poorly understood properties such as surface roughness and topography are provided, together with the need for further studies relevant to biomimetic and sensing purposes.

Pyrolysis of Methyl Formate and the Reaction of Methyl Formate with H Atoms: Shock Tube Experiments and Statistical Rate Theory.

Methyl formate (MF) is the smallest carboxylic ester and currently considered a promising alternative fuel. It can also serve as a model compound to study the combustion chemistry of the ester group, which is a typical structural feature in many biodiesel components. In the present work, the pyrolysis of MF was investigated behind reflected shock waves at temperatures between 1430 and 2070 K at a nominal pressure of 1.1 bar. Both time-resolved hydrogen atom resonance absorption spectroscopy (H-ARAS) and time-resolved time-of-flight mass spectrometry (TOF-MS) were used for species detection. Additionally, the reaction of MF and perdeuterated MF-d4 with H atoms was investigated at temperatures between 1000 and 1300 K at nominal pressures of 0.4 and 1.1 bar with H-ARAS. In the latter experiments, ethyl iodide served as precursor for H atoms. Rate coefficients of seven parallel unimolecular decomposition channels of MF and five parallel reaction channels of the MF + H reaction were calculated from statistical rate theory on the basis of molecular and transition state data from quantum chemical calculations. These calculated rate coefficients were implemented into an MF pyrolysis/oxidation mechanism from the literature, and the experimental concentration-time profiles of H (from ARAS) as well as MF, CH3OH, HCHO, and CO (from TOF-MS) were modeled. It turned out that the literature mechanism, which was originally validated against flow-reactor experiments, ignition delay times, and laminar burning velocities, was generally able to fit also the concentration-time profiles from the shock tube experiments reasonably well. The agreement could still be improved by substituting the original rate coefficients, which were estimated from structure-reactivity relationships, by the values calculated from statistical rate theory in the present work. Details of the channel branching are discussed, and the updated mechanism is given, also in machine-readable form.

Atom-based sensing technique of microwave electric and magnetic fields via a single rubidium vapor cell.

We present an atom-based approach for determining microwave electric and magnetic fields by using a single rubidium vapor cell in a microwave waveguide. For a 87Rb cascade three-level system employed in our experiment, a weak probe laser driving the lower transition, 5S1/2→5P3/2, is first used to measure the microwave magnetic field based on the atomic Rabi resonance. When a counter-propagating strong coupling laser is subsequently turned on to drive the Rydberg transition, 5P3/2→67D5/2, the same probe laser is then used as a Rydberg electromagnetically induced transparency (EIT) probe to measure the microwave electric field by investigating the resonant microwave dressed Autler-Townes splitting (ATS). By tuning the hyperfine transition frequency of the ground state using an experimentally feasible static magnetic field, we first achieved a measurement of the microwave electric and magnetic field strength at the same microwave frequency of 6.916 GHz. Based on the ideal relationship between the electric and magnetic field components, we obtained the equivalent microwave magnetic fields by fitting the inversion to the measured microwave electric fields, which demonstrated that the results were in agreement with the experimental measurement of the microwave magnetic fields in the same microwave power range. This study provides new experimental evidence for quantum-based microwave measurements of electric and magnetic fields by a single sensor in the same system.

Thermometry of liquid water through slow light imaging spectroscopy.

This work presents the first, to the best of our knowledge, experimental demonstration of slow light imaging spectroscopy for thermometry of liquid water. This novel technique for measuring temperature relies on detecting the spectral shift of Brillouin peaks in water using the temporal delay through a cell containing an atomic vapor. Stand-off sensing capabilities are achieved by time-domain measurements of Brillouin scattering tuned to be near a rubidium atomic resonance and passed through a cell filled with rubidium vapor. An injection seeded optical parametric oscillator (OPO) is demonstrated to be a versatile light source for slow light imaging spectroscopy applications. The narrow OPO pulse spectrum allows for a precise profiling of slow light features of rubidium and accurate tracking of the temperature dependence of Brillouin scattering spectral shift. A comparison between the experimental data and numerical simulation over a temperature range of 20 to 99 degrees Celsius shows a good agreement for both qualitative and quantitative results.

Quantum Measurement of Radio-Frequency Attenuation Based on Atomic Resonance

Quantum Measurement of Radio-Frequency Attenuation Based on Atomic Resonance

High-Yield Production of Quantum Corrals in a Surface Reconstruction Pattern

The power of surface chemistry to create atomically precise nanoarchitectures offers intriguing opportunities to advance the field of quantum technology. Strategies for building artificial electronic lattices by individually positioning atoms or molecules result in precisely tailored structures but lack structural robustness. Here, taking the advantage of strong bonding of Br atoms on noble metal surfaces, we report the production of stable quantum corrals by dehalogenation of hexabromobenzene molecules on a preheated Au(111) surface. The byproducts, Br adatoms, are confined within a new surface reconstruction pattern and aggregate into nanopores with an average size of 3.7 ± 0.1 nm, which create atomic orbital-like quantum resonance states inside each corral due to the interference of scattered electron waves. Remarkably, the atomic orbitals can be hybridized into molecular-like orbitals with distinct bonding and antibonding states. Our study opens up an avenue to fabricate quantum structures with high yield and superior robustness.

Enhancing mechanism of CNT-CNT interface by metal nanoparticle and nanowire effect on the inside and outside of CNT

Enhancing the weak interfacial heat transfer between carbon nanotubes (CNTs) is an effective approach to its application in thermal management for electronic devices, MEMS, etc. The conventional methods of strengthening thermal conductance (G) between CNTs have not reached expectations, and thus it is necessary to develop a new enhancement way. This work systematically studies potential enhancement ways by molecular dynamics simulation. It is found that the direct loading of nano particles (NPs) between CNTs, the indirect loading of nanowires (NWs) into CNTs, and the synergistic loading of both clusters and NWs can have some positive effects. The loaded cluster and NW involves six metals (Cu, Ag, Au, Pt, Ni and Rh). The results show that the cluster with large amount low frequency phonon (LFP) induces LFP resonance of interfacial carbon atoms in CNTs, resulting in the remarkable enhancement of G. After loading NW into CNT, NW and NP synergistically produce resonance effect on the phonons of interfacial carbon atoms in CNT, and the G can be further improved by 29% after NW loading.

Probing ultrafast excited-state dynamics using EUV-IR six-wave-mixing emission spectroscopy.

Non-linear processes such as four-wave-mixing have become instrumental in attosecond EUV spectroscopy. Using EUV high harmonics in conjunction with collinear near-infrared and mid-infrared fields, we extended this approach to high-order-mixing between three colors. Specifically, we find that atomic resonances in neon exhibit a significant cross section for six-wave mixing. The MIR probe frequency tunability in our multicolor scheme is employed to access several optically dark resonances and probe the quantum beat of a coherent electronic wavepacket using background-free EUV emission as a diagnostic. This technique can be easily extended to other atomic and molecular systems, and opens the door to multi-dimensional non-linear spectroscopy.

Humidity effect on real-time response of tetranitro-oxacalix[4]arene-based surface plasmon resonance (SPR) acetone sensor at room temperature

We report the effect of humidity on the acetone sensitivity of nano-sized thin films obtained by spin coating the oxacalix[4]arenes(1,3) molecules on suitable substrates in this work. The surface morphologies and volatile organic compound (VOC) sensor properties of spin-coated thin films were examined using atomic force microscopy (AFM) and surface plasmon resonance (SPR), respectively. It was determined that the sensitivities calculated from the measurements performed using a mixture of acetone and water vapor were 14% and 11% incorrect for the 1 and 3 thin film sensors, respectively, compared to those performed with dry air and acetone mixture.

First Observation of New Flat Line Fano Profile via an X-Ray Planar Cavity.

A new Fano profile of a flat line is achieved experimentally by manipulating the relative amplitude of the continuum path, when q takes the pure imaginary number of -i in the x-ray regime. The underlying mechanism is that the interference term in the scattering will cancel the discrete term exactly. This new Fano profile renders only an observable continuum along with an invisible response to the discrete state of atomic resonance. The results suggest not only a different strategy to invisibility studies which provides a possible tool to identify weaker structures hidden by the strong white line, but also a new scenario to enrich the manipulations of two-path interference and nonlinear Fano resonance.

Laser spectroscopic studies of long-lived pionic helium at PSI

A recent laser spectroscopy experiment of three-body pionic helium atoms which was carried out using the 590 MeV ring cyclotron facility of the Paul Scherrer Institute (PSI) is briefly reviewed. The charged pion mass may be precisely determined by measuring the transition frequency of the pionic atom and comparing the results with quantum electrodynamics (QED) calculations. The experimental methods used to detect the atomic resonance are described.

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.

Atom Interferometry with Floquet Atom Optics.

Floquet engineering offers a compelling approach for designing the time evolution of periodically driven systems. We implement a periodic atom-light coupling to realize Floquet atom optics on the strontium ^{1}S_{0}-^{3}P_{1} transition. These atom optics reach pulse efficiencies above 99.4% over a wide range of frequency offsets between light and atomic resonance, even under strong driving where this detuning is on the order of the Rabi frequency. Moreover, we use Floquet atom optics to compensate for differential Doppler shifts in large momentum transfer atom interferometers and achieve state-of-the-art momentum separation in excess of 400 ℏk. This technique can be applied to any two-level system at arbitrary coupling strength, with broad application in coherent quantum control.

Rheology and early microstructure evolution of fresh ultra-high performance concrete with polycarboxylate superplasticizer

Polycarboxylate superplasticizer (PCE) is a key ingredient in the preparation of ultra-high performance concrete (UHPC). However, it is still unclear how PCE affects hydration and microstructure evolution of UHPC, and how it changes the rheological properties over time. In this paper, the rheological properties in the early 5 h were measured by rotational and oscillatory shear tests, and solid and liquid phase composition were analyzed by thermogravimetric analysis, atomic emission spectrometer and 1H nuclear magnetic resonance relaxation method (1H NMR). The results show that the free water content in fresh concrete decreases with time, and the particle void shrinks, resulting in a smaller space for water distribution. As the particle void decreases from 139.89 nm to 121.665 nm, the plastic viscosity and storage modulus increases rapidly, and the mixture loses fluidity when average void size is less than 105.825 nm. After increasing the content of PCE in UHPC, the formation of early hydration products was inhibited, and the shrinkage of particle void in the slurry slowed down, leading to the decreasing of the plastic viscosity of UHPC over time.

High-partial-wave separable potential method for investigating Feshbach resonances of ultracold atoms

We present a high-partial-wave (non-zero partial-wave) separable potential method (SPM) for investigating magnetically induced Feshbach resonances in collisions of ultracold atoms, then derive the Lippmann–Schwinger equation for two ultracold alkali-metal atoms in an external magnetic field and calculate the generalized scattering length and weakly bound state energy. We apply this method to the 6Li system and calculate the weakly bound state energy and the scattering volume near three typical p-wave Feshbach resonances. The calculated results by using the SPM agree well with those by using the coupled channel method and with experimental measurements. The SPM is expected to simplify computation of the three-body collision Faddeev equation in the vicinity of two-body high partial-wave Feshbach resonances.

Continuous Variable Entanglement in an Optical Parametric Oscillator Based on a Nondegenerate Four Wave Mixing Process in Hot Alkali Atoms.

We present the measurement of entanglement between twin beams generated with a doubly resonant optical parameter oscillator (OPO) based on four-wave mixing in hot ^{85}Rb vapor above threshold. This is the first measurement of entanglement in an OPO with a χ^{(3)} media above threshold. We reconstruct the covariance matrix for several configurations and based on a full picture of the four side band mode state, we study entanglement between all possible bipartitions. We show a robust generation of entanglement with stronger generation for a specific pair of modes. For this system, we show that atomic density is a determinant factor for the generation and loss of quantum correlations. The generation of entangled fields with an atomic OPO operating close to atomic resonance of alkali atoms enables a natural integration into quantum networks.

Fano-like Resonance due to Interference with Distant Transitions.

Narrow optical resonances of atoms or molecules have immense significance in various precision measurements, such as testing fundamental physics and the generation of primary frequency standards. In these studies, accurate transition centers derived from fitting the measured spectra are demanded, which critically rely on the knowledge of spectral line profiles. Here, we propose a new mechanism of Fano-like resonance induced by distant discrete levels and experimentally verify it with Doppler-free spectroscopy of vibration-rotational transitions of CO_{2}. The observed spectrum has an asymmetric profile and its amplitude increases quadratically with the probe laser power. Our results facilitate a broad range of topics based on narrow transitions.

Investigation of electron-induced scattering resonances using a multiconfigurational polarization propagator and a complex absorbing potential

We develop a method based on the polarization propagator (PP) combined with the complex absorbing potential (CAP) technique to study metastable resonances induced by electron impact. We use a CASSCF wavefunction corresponding to the ground state of the anion as the initial state for the PP. The perturbation of the Hamiltonian by the CAP allows for complex eigenvalues that represent the continuum states including the resonance buried in the continuum. The artifacts due to the CAP are eliminated using the Padé extrapolation method. We apply our method to study the 2P Be− atomic shape resonance, and 2Πg N2− and 2Π CO− molecular shape resonances. Our estimated resonance positions and widths for the resonances are in agreement with the previously reported values. Overall, this method is a powerful and computationally tractable tool for the study of resonances.

Influence of an atomic resonance on the coherent control of the photoionization process

In coherent control schemes, pathways connecting an initial and a final state can be independently controlled by manipulating the complex amplitudes of their transition matrix elements. For paths characterized by the absorption of multiple photons, these quantities depend on the magnitude and phase between the intermediate steps, and are expected to be strongly affected by the presence of resonances. We investigate the coherent control of the photoemission process in neon using a phase-controlled two-color extreme ultraviolet pulse with frequency in proximity of an excited energy state. Using helium as a reference, we show that the presence of such a resonance in neon modifies the amplitude and phase of the asymmetric emission of photoelectrons. Theoretical simulations based on perturbation theory are in fair agreement with the experimental observations.Received 25 July 2021Revised 1 August 2022Accepted 5 August 2022DOI:https://doi.org/10.1103/PhysRevResearch.4.033231Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasMultiphoton or tunneling ionization & excitationPhotoemissionSingle- and few-photon ionization & excitationUltrafast phenomenaUltrashort pulsesAtomic, Molecular & Optical