SEARCH · Searcharxiv

Results for “physics.atom-ph”

Search indexed arXiv papers on artificial intelligence, large language models, computer vision and robotics. Read source abstracts and follow links to arXiv.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources

arXiv2008

A Microscpoic Model for the Neutron Dynamic Structure Factor of Solid Methane in phase II

We have constructed an approximate microscopic model for the neutron dynamic structure factor of solid methane in phase II. We expect our model to apply for neutron energies below 1\textit{eV} at pressures near 1 bar and temperatures below 20K, where solid methane exists in a phase, called phase II, in which the tetrahedral hydrogens exist in a mixed phase of free rotors and hindered rotors. Certain matrix elements needed for the dynamic structure factor $S(Q, ω)$ are adapted from a calculation by Ozaki \textit{et al.}\cite{ozaki:3442}\cite{ozaki2}. The model treats the effects of molecular translations, intramolecular vibrations and the free and hindered rotational degrees of freedom as uncoupled ones. Total scattering cross sections calculated from the model agree with the cross section measurements of Grieger\cite{grieger:3161} and Whittemore\cite{Wittemore} for the incident neutron energies of 0.5 \textit{meV} $\sim$ 1\textit{eV}. The effective density of states extracted from the model was compared with the Harker $&$ Brugger frequency spectrum extracted from neutron scattering measurements conducted at 22K\cite{HARKER1967}.

physics.atom-ph↗

arXiv2009

Atomtronic circuits of diodes and transistors

We illustrate that open quantum systems composed of neutral, ultracold atoms in one-dimensional optical lattices can exhibit behavior analogous to semiconductor electronic circuits. A correspondence is demonstrated for bosonic atoms, and the experimental requirements to realize these devices are established. The analysis follows from a derivation of a quantum master equation for this general class of open quantum systems.

physics.atom-ph↗

arXiv2007

Coulomb oscillations as a remedy for the helium atom

The largest failure of the old, Bohr-Sommerfeld quantum theory was with the helium atom. It brought about the theory's demise. I show that this failure does not originate, as commonly believed, with the orbit concept per se. Instead, it was caused by the wrong choice of orbits, compounded by ignorance of the exclusion principle. Choosing semiclassical electron oscillations through the He nucleus, I calculate a singlet ground-state energy that rivals in accuracy with quantum-mechanical results. The same method reveals Bohr's historic energy value as the forbidden triplet ground state--a result beyond the reach of quantum mechanics. At the qualitative level, the concept of Coulomb oscillations visually explains the major features in the He double spectrum in terms of crossed or parallel orbit orientation.

physics.hist-ph↗

arXiv2007

The Volume Capture in Structures with Variable Curvature

The volume capture in classical relativistic mechanics is considered as a scattering process for the high energy charged particles in a field with no central or mirror symmetry. The parameters of volume capture for potentials with smooth variable curvature are received and analyzed.

physics.acc-ph↗

arXiv2007

Teleportation of massive particles without shared entanglement

We propose a method for quantum state transfer from one atom laser beam to another via an intermediate optical field, using Raman incoupling and outcoupling techniques. Our proposal utilises existing experimental technologies to teleport macroscopic matter waves over potentially large distances without shared entanglement.

quant-ph↗

arXiv2007

High-harmonic generation in diatomic molecules: a quantum-orbit analysis of the interference patterns

We perform a detailed analysis of high-order harmonic generation in diatomic molecules within the strong-field approximation, with emphasis on quantum-interference effects. Specifically, we investigate how the different types of electron orbits, involving one or two centers, affect the interference patterns in the spectra. We also briefly address the influence of the choice of gauge, and of the initial and final electronic bound states on such patterns. For the length-gauge SFA and undressed bound states, there exist additional terms, which can be interpreted as potential energy shifts. If, on the one hand, such shifts alter the potential barriers through which the electron initially tunnels, and may lead to a questionable physical interpretation of the features encountered, on the other hand they seem to be necessary in order to reproduce the overall maxima and minima in the spectra. Indeed, for dressed electronic bound states in the length gauge, or undressed bound states in the velocity gauge, for which such shifts are absent, there is a breakdown of the interference patterns. In order to avoid such a problem, we provide an alternative pathway for the electron to reach the continuum, by means of an additional attosecond-pulse train. A comparison of the purely monochromatic case with the situation for which the attosecond pulses are present suggests that the patterns are due to the interference between the electron orbits which finish at different centers, regardless of whether one or two centers are involved.

physics.atom-ph↗

arXiv2007

Phase Transition of Trapped Nuclear Exciton of Long-lived Rhodium Mossbauer States

We report experimental observations of the long-lived rhodium Mossbauer emissions by the time- and energy-resolved spectroscopy. The extraordinary observations manifest the open-up of photonic band gap in analogy to the superconducting gap of remarkable symmetry breakings at transition point. These observations are of potential importance for detecting gravitational waves and development of the two-photon gamma laser. Firstly, phase transitions shown by spectral evolution of characteristic emissions reveal the different aggregate exciton orderings at room temperature. Six different phases are identified by spectra profiles emitted from the color centers. Secondly, the cascade branching of the multipolar nuclear transition is discovered being the spontaneous cascade down-conversion to generate entangled gammas. The macroscopic angular distribution of entangled gammas from the polycrystalline sample manifests a global photon-nucleus-photon bound state across the grain boundaries. Thirdly, the gamma-energy distributions depending on exciton phases reveal the photonic band gap typically on the order of several hundred eV.

quant-ph↗

arXiv2007

Dependence of Resonant Absorption Linewidth on Atomic Vapour Column Thickness for D1 Line of Cs Atoms Confined in Nano-Cell

A new nano-cell with smoothly varying longitudinal thickness of the atomic vapour layer L in the range of 350 - 5100 nm allowing to study the resonant absorption of D1 and D2 lines of Cs atoms for thicknesses changing from L = Lambda/2 to L = 6 Lambda with the step of Lambda/2 (Lambda = 852 nm or 894 nm are the resonant laser wavelengths) and for different intensities is developed. It is revealed that for low laser intensities there is narrowing of the resonant absorption spectrum for the thicknesses L = (2n + 1)Lambda/2 (where n is an integer) up to L = 7Lambda /2 and broadening of the spectrum for L = n Lambda. For relatively high laser intensity (>1 mW/cm2), velocity selective optical pumping/saturated resonances of a reduced absorption (with the line-width close to the natural one), and centred on the hyperfine transitions occur when L = n Lambda. The possible application of these resonance peaks is given. The developed theoretical model describes well the experiment.

physics.atom-ph↗

arXiv2007

Rhodium Mossbauer Superradiance of Observable Gravitational Effect

We summarize the experimental observations of three case studies on the long-lived rhodium Mossbauer Effect. Extraordinary observations reported in this work manifest the open-up of photonic band gap in analogy to the superconducting gap. Observable gravitational effect is manifested by the superradiance of different sample orientations corresponding to the earth gravity. These observations are of potential importance for detecting gravitational waves and development of the two-photon gamma laser.

quant-ph↗

arXiv2007

Theoretical spectroscopic studies of the atomic transitions and lifetimes of low-lying states in Ti IV

The astrophysically important electric quadrupole (E2) and magnetic dipole (M1) transitions for the low-lying states of triply ionized titanium (Ti IV) are calculated very accurately using a state-of-art all-order many-body theory called Coupled Cluster (CC) theory in the relativistic frame-work. Different many-body correlations of the CC theory has been estimated by studying the core and valence electron excitations to the unoccupied states. The calculated excitation energies of different states are in very good agreement with the measurements. Also we compare our calculated electric dipole (E1) transition amplitudes of few transitions with recent many-body calculations by different groups. We have also carried out the calculations for the lifetimes of the low-lying states of Ti IV. A long lifetime is found for the first excited 3d$^{2}D_{5/2}$ state, which suggested that Ti IV may be one of the useful candidates for many important studies. Most of the results reported here are not available in the literature, to the best of our knowledge.

physics.atom-ph↗

arXiv2008

Shape resonances in modified effective range theory for electron-molecule collisions

We develop a simple model of shape resonances in electron-molecule collisions that is based on the modified effective-range expansion and analytical solutions of the Schrodinger equation for the long-range part of the interaction potential. We apply our model to electron scattering on N$_2$ and CO$_2$. The parameters of the effective-range expansion (i.e. the scattering length and the effective range) are determined from experimental, integral elastic cross sections in the 0.1 - 1.0 eV energy range. For both molecular targets our treatment predicts shape resonances that appear slightly higher than experimentally known resonances in total cross sections. Agreement with the experiment can be improved by assuming the position of the resonance in a given partial wave. Influence of quadrupole potential on resonances is also discussed: it can be disregarded for N$_2$ but gets significant for CO$_2$. In conclusion, our model developed within the effective range formalism reproduces well both the very low-energy behavior of the integral cross section as well as the presence of resonances in the few eV range.

physics.atom-ph↗

arXiv2007

Deflection of ultra slow light under gravity

Recent experiments on ultra slow light in strongly dispersive media by several research groups reporting slowing down of the optical pulses down to speeds of a few metres per second encourage us to examine the intriguing possibility of detecting a deflection or fall of the ultra slow light under Earth's gravity, i.e., on the laboratory length scale. In the absence of a usable general relativistic theory of light waves propagating in such a strongly dispersive optical medium in the presence of a gravitational field, we present a geometrical optics based derivation that combines {\it the effective gravitational refractive index} additively with the usual optical dispersion. It gives a deflection, or the vertical fall $Δ$ for a horizontal traversal $L$ as \[ Δ= \frac{L^2}{2}\big(\frac{R_{\oplus G}}{R_\oplus^2}\big) n_g \big(\frac{1}{1+n_g\frac{R_{\oplus G}}{R_\oplus}}\big), \] where $R_{\oplus G}/R_\oplus$ is the ratio of the gravitational Earth radius($R_{\oplus G}$) to its geometrical radius $R_\oplus$, and $n_g$ is the group refractive index of the strongly dispersive optical medium. The expression is essentailly that for the Newtonian fall of an object projected horizontally with the group speed $v_g=c/n_g$, and is tunable refractively through the index $n_g$. For $L \sim 1 m$ and $n_g = c/v_g \sim 10^8$ (corresponding to the ultra-slow pulse speed $\sim few \times 1 ms^{-1}$), we obtain a fall $Δ\sim 1 μm$, that should be measurable $-$ in particular through its sensitive dependence on the frequency that tunes $n_g$.

physics.optics↗

arXiv2008

Antiproton-deuteron atoms in models of realistic potentials

The antiproton-deuteron atoms are studied in models of various realistic, popular nucleon-antinucleon potentials. The small energy shifts and decay widths of the atoms, which stem from the short-ranged strong interactions between the antiproton and deuteron, are evaluated in a well-established, accurate approach based on the Sturmian functions. The investigation reveals that none of the employed potentials, which reproduce the nucleon-antinucleon scattering data quite well, is able to reproduce the experimental data of the energy shifts of the 2p antiproton-deuteron atomic states. The energy shifts of the 2p antiproton-deuteron atomic states are very sensitive to the nucleon-antinucleon strong interactions, hence the investigation of the antiproton-deuteron atoms is expected to provide a good platform for refining the nucleon-antinucleon interaction, especially at zero energy.

physics.atom-ph↗

arXiv2007

A Weyl function approach to matter-wave coherence and Talbot-Lau effects

Weyl functions conveniently describe the evolution of wave coherences in periodic or quadratic potentials. In this work we use Weyl functions to study the ``Talbot-Lau effect'' in a time-domain matter-wave interferometer. A ``displacement diagram'' is introduced to analyze and calculate the matter-wave interference for an atomic cloud in a quadratic potential that interacts with a sequence of short optical standing wave pulses producing an atomic grating echo. Unlike previous treatments, this new approach allows the atomic ensemble to have an arbitrary initial phase-space distribution, and the standing wave grating vectors to span three dimensions. Several examples are discussed to illustrate the convenience of the diagrammatic technique including the following: a two-dimensional Talbot-Lau effect, the shift in the echo time and the recoil phase for the interferometer perturbed by a quadratic potential; and the realization of a time-domain ``Lau effect'' using a pulsed harmonic potential. The diagrammatic technique is applicable to diffraction gratings with arbitrary grating transmission functions. We conclude the paper with a general discussion on the Weyl function representations of matter-wave coherence, and relate the conservation of matter-wave coherence with the conservation of purity that distinguishes decoherence effects from dephasing effects.

physics.atom-ph↗

arXiv2011

Sub-natural width of transparency window in 85Rb vapor with D2 transition,

We study 85Rb atomic vapor for electromagnetically induced transparency (EIT) and obtain sub-natural EIT spectra at optical power higher than saturation intensity. It is shown that spectral width of transmission and intensity of EIT signal increases with intensity of optical field, which is one of the desirable features for slow light and quantum information processing. A details analysis has been done on such an atomic system.

physics.atom-ph↗

arXiv2011

Wide range and highly sensitive atomic magnetometry with Rb vapor

We have developed a technique in which Rb atomic response to weak magnetic field is high and an efficient rotation of linearly polarized laser beam results in efficient magnetometry. 85Rb isotope has been used for the magnetometry in an ordinary vapor cell without any paraffin coating to its inner wall. A linear regime of Faraday rotation of about 25 microT has been observed with atomic number density within the vapor cell of about 10^9 cm-3.

physics.atom-ph↗

arXiv2008

Studying variation of fundamental constants with molecules

This review article is devoted to application of precision molecular spectroscopy to studies of the possible spatial and temporal variations of the fundamental constants. Both astrophysical observations and laboratory experiments are discussed.

physics.atom-ph↗

arXiv2009

Excitation energies from ground-state density-functionals by means of generator coordinates

The generator-coordinate method is a flexible and powerful reformulation of the variational principle. Here we show that by introducing a generator coordinate in the Kohn-Sham equation of density-functional theory, excitation energies can be obtained from ground-state density functionals. As a viability test, the method is applied to ground-state energies and various types of excited-state energies of atoms and ions from the He and the Li isoelectronic series. Results are compared to a variety of alternative DFT-based approaches to excited states, in particular time-dependent density-functional theory with exact and approximate potentials.

physics.chem-ph↗