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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Dynamical electron vortices in attosecond double photoionization of H 2

We study electron momentum vortices in single-photon double ionization of H 2 by time-delayed, counter-rotating, elliptically polarized attosecond pulses propagating along kˆ either parallel or perpendicular to the molecular axis R. For ˆk∥R, kinematical vortices occur similar to those found for He. For kˆ⊥R, we find dynamical vortex structures originating from an ellipticity-dependent interplay of 1 Σ$^{+}_{u}$ and 1 Π$^{+}_{u}$ continuum amplitudes. Furthermore, we propose a complete experiment to determine the magnitudes and relative phase of these amplitudes by varying pulse ellipticities and time delays.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Proton-beam stopping in hydrogen

The stopping cross section for protons passing through hydrogen is calculated for the energy range between 10 keV and 3 MeV. Both the positive and neutral charge states of the projectile are accounted for. The two-center convergent close-coupling method is used to model proton collisions with hydrogen. In this approach, electron-capture channels are explicitly included by expanding the scattering wave function in a basis of both target and projectile pseudostates. Hydrogen collisions with hydrogen are modeled using two methods: the single-center convergent close-coupling approach is used for the calculation of one-electron processes, while two-electron processes are calculated using the Born approximation. The aforementioned approaches are also applied to the calculation of the charge-state fractions. Furthermore, these are then used to combine the proton-hydrogen and hydrogen-hydrogen stopping cross sections to yield the total stopping cross section for protons passing through hydrogen.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Pulse-duration dependence of the double-to-single ionization ratio of Ne by intense 780-nm and 800-nm laser fields: Comparison of simulations with experiments

Accurate ab initio calculations of the ratio of double-to-single ionization of Ne atoms in strong laser fields are difficult due to the many-electron nature of the target. Here, with accurate total cross sections carefully evaluated by using the state-of-the-art many-electron R-matrix theory for both electron-impact ionization and electron-impact excitation of Ne + , we simulate the total double-ionization yields of Ne 2+ in strong laser fields at 780 and 800 nm for pulse durations in the range from 7.5 to 200 fs based on the improved quantitative rescattering model. The corresponding single-ionization yields of Ne + are calculated within the nonadiabatic tunneling model of Perelomov, Popov, and Terent'ev. The ratio of double-to-single ionization of Ne is then obtained from the calculated double- and single-ionization yields. By normalizing the ratio to the one calculated from solving the time-dependent Schrödinger equation for a short few-cycle pulse, we make quantitative comparisons of our results with experimental data to show that our model predicts the experimental findings very well. Lastly, we analyze the pulse-duration dependence of the double-to-single ionization ratio.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Phase-dependent ionization of Rydberg atoms in static fields

Using a laser intensity modulated synchronously with a 15.9 GHz microwave field we have examined laser excitation of Li atoms to the vicinity of the ionization limit in the presence of the microwave field and a parallel static field. The static field breaks the symmetry of ionization in the two microwave half cycles, and as the intensity modulated laser beam is delayed relative to the microwave field, maxima in the ionization are observed every microwave field cycle, not every half cycle, as in the absence of the static field. Here, when the laser is tuned below the ionization limit there is an unexpected phase reversal of the modulation in the ionization, the origin of which is clarified by a classical model.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1991

High frequency scattering from trihedral corner reflectors and other benchmark targets - SBR versus experiment

A general method for calculating the radar cross section (RCS) from a three-dimensional target is described. The target is first constructed by using a solid-geometry-modeling computer-aided design (CAD) package. Following the shooting and bouncing ray (SBR) method, a very dense grid of rays is launched from the incident direction toward the target. Each ray is traced according to the geometrical optics theory including the effect of ray tube divergence, polarization, and material reflection coefficient. At the point where the ray exits the target, a physical optics-type integration is performed to obtain the scattered far fields. This method is tested using several simple examples involving interaction among plates, cylinders, and spheres. The theoretical results are generally in good agreement with measured data.

Baldauf, John↗
DOE OSTI2015

Nanophotonic quantum computer based on atomic quantum transistor

We propose a scheme of a quantum computer based on nanophotonic elements: two buses in the form of nanowaveguide resonators, two nanosized units of multiatom multiqubit quantum memory and a set of nanoprocessors in the form of photonic quantum transistors, each containing a pair of nanowaveguide ring resonators coupled via a quantum dot. The operation modes of nanoprocessor photonic quantum transistors are theoretically studied and the execution of main logical operations by means of them is demonstrated. We also discuss the prospects of the proposed nanophotonic quantum computer for operating in high-speed optical fibre networks. (quantum computations)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Relation between absorption and emission directivities for dipoles coupled with optical antennas

Optical antennas have been widely used to control the absorption and emission properties of dipole emitters. Understanding the relationship between the absorption and emission processes of such dipole emitters in the presence of optical antennas is therefore of fundamental importance. Here we provide an in-depth analysis of the relationship between the absorption and emission directivities of dipoles coupling to optical antennas. Here, we show that, for reciprocal systems, the absorption and emission directivities are identical for a single dipole emitter, and also in the case of multiple dipole emitters when one considers incoherent emission from the emitters. On the other hand, in general, the coherent emission directivities of the dipoles are always different from the absorption directivities in the multiple-dipole case. But there are special situations in the multiple-dipole case where the coherent emission has directivities that are approximately the same as the absorption directivity. This study clarifies the relation between absorption and emission directivities for emitters coupled with optical antennas and may provide useful insights into the design and characterization of optical antennas for various applications.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRSDate not supplied

MISR Level 2 Aerosol parameters (MIL2ASAE_V1)

The Aerosol data contain aerosol optical depth, aerosol physical model, ancillary meteorological data, and related parameters. The aerosol data include tropospheric aerosol optical depth, Angstrom exponent and single scattering albedo on 17.6 km centers, aerosol mixture identifier and retrieval residuals, and ancillary data including assumed ozone optical depth and retrieval flags. For complete information about the aerosol mixtures, the user will need to order the MISR Aerosol Climatology Product (MIANACP) to obtain Aerosol Physical and Optical Properties (APOP) and the Mixture files. The Mixture files list up to 3 component models used in each mixture, with their relative compositional fractions, and includes ancillary information such as single scattering albedo. The APOP gives detailed information for the component particle models. [Location=GLOBAL] [Temporal_Coverage: Start_Date=2000-02-24; Stop_Date=] [Spatial_Coverage: Southernmost_Latitude=-90; Northernmost_Latitude=90; Westernmost_Longitude=-180; Easternmost_Longitude=180] [Data_Resolution: Latitude_Resolution=1.1 km - 17.6 km; Longitude_Resolution=1.1 km - 17.6 km; Horizontal_Resolution_Range=1 km - < 10 km or approximately .01 degree - < .09 degree; Temporal_Resolution=about 15 orbits/day].

CIRRUS OPTICAL DEPTH↗
NASA NTRSDate not supplied

MISR Level 2 Aerosol parameters (MIL2ASAE_V2)

The Aerosol data contain aerosol optical depth, aerosol physical model, ancillary meteorological data, and related parameters. The aerosol data include tropospheric aerosol optical depth, Angstrom exponent and single scattering albedo on 17.6 km centers, aerosol mixture identifier and retrieval residuals, and ancillary data including assumed ozone optical depth and retrieval flags. For complete information about the aerosol mixtures, the user will need to order the MISR Aerosol Climatology Product (MIANACP) to obtain Aerosol Physical and Optical Properties (APOP) and the Mixture files. The Mixture files list up to 3 component models used in each mixture, with their relative compositional fractions, and includes ancillary information such as single scattering albedo. The APOP gives detailed information for the component particle models. [Location=GLOBAL] [Temporal_Coverage: Start_Date=2000-02-24; Stop_Date=] [Spatial_Coverage: Southernmost_Latitude=-90; Northernmost_Latitude=90; Westernmost_Longitude=-180; Easternmost_Longitude=180] [Data_Resolution: Latitude_Resolution=1.1 km - 17.6 km; Longitude_Resolution=1.1 km - 17.6 km; Horizontal_Resolution_Range=1 km - < 10 km or approximately .01 degree - < .09 degree; Temporal_Resolution=about 15 orbits/day; Temporal_Resolution_Range=Daily - < Weekly, Daily - < Weekly].

EOSDIS↗
DOE OSTI2021

Singularities in nearly uniform one-dimensional condensates due to quantum diffusion

Dissipative systems often exhibit wavelength-dependent loss rates. One prominent example is Rydberg polaritons formed by electromagnetically induced transparency, which have long been a leading candidate for studying the physics of interacting photons and also hold promise as a platform for quantum information. In this system, dissipation is in the form of quantum diffusion, i.e., proportional to k 2 (k being the wavevector) and vanishing at long wavelengths as k→0. Here, we show that one-dimensional condensates subject to this type of loss are unstable to long-wavelength density fluctuations in an unusual manner: after a prolonged period in which the condensate appears to relax to a uniform state, local depleted regions quickly form and spread ballistically throughout the system. We connect this behavior to the leading-order equation for the nearly uniform condensate—a dispersive analog to the Kardar-Parisi-Zhang equation—which develops singularities in finite time. Furthermore, we show that the wavefronts of the depleted regions are described by purely dissipative solitons within a pair of hydrodynamic equations, with no counterpart in lossless condensates. We close by discussing conditions under which such singularities and the resulting solitons can be physically realized.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Microwave spectroscopy of the Yb 6 s ( n + 3 ) d → 6 s n g , 6 s n h , and 6 s n i transitions

Using a microwave and radio frequency resonance approach we observe the transitions of ytterbium from the 6s(n + 3)d states to the 6snℓ states for 4 ≤ ℓ ≤ 6 and 28 ≤ n ≤ 33. The energies of the 6snℓ states of ℓ ≥ 4 are determined from the observed intervals and the known values of the 6snd energies. Here, we use a nonadiabatic core polarization model to analyze the energy levels to determine the dipole (α d ) and quadrupole (α q ) polarizabilities of the ground state of Yb + . We find the values α d = 60.51 (10) $a$ $^{3}_{0}$ and α q = 672 (28) $a$ $^{5}_{0}$.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Atomic resolution coherent x-ray imaging with physics-based phase retrieval

Coherent x-ray imaging and scattering from accelerator based sources such as synchrotrons continue to impact biology, medicine, technology, and materials science. Many synchrotrons around the world are currently undergoing major upgrades to increase their available coherent x-ray flux by approximately two orders of magnitude. The improvement of synchrotrons may enable imaging of materials in operando at the atomic scale which may revolutionize battery and catalysis technologies. Current algorithms used for phase retrieval in coherent x-ray imaging are based on the projection onto sets method. These traditional iterative phase retrieval methods will become more computationally expensive as they push towards atomic resolution and may struggle to converge. Additionally, these methods do not incorporate physical information that may additionally constrain the solution. In this work, we present an algorithm which incorporates molecular dynamics into Bragg coherent diffraction imaging (BCDI). This algorithm, which we call PRAMMol (Phase Retrieval with Atomic Modeling and Molecular Dynamics) combines statistical techniques with molecular dynamics to solve the phase retrieval problem. We present several examples where our algorithm is applied to simulated coherent diffraction from 3D crystals and show convergence to the correct solution at the atomic scale.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Probabilistic simulation of quantum circuits using a deep-learning architecture

The fundamental question of how to best simulate quantum systems using conventional computational resources lies at the forefront of condensed matter and quantum computation. It impacts both our understanding of quantum materials and our ability to emulate quantum circuits. Here we present an exact formulation of quantum dynamics via factorized generalized measurements which maps quantum states to probability distributions with the advantage that local unitary dynamics and quantum channels map to local quasistochastic matrices. This representation provides a general framework for using state-of-the-art probabilistic models in machine learning for the simulation of quantum many-body dynamics. Using this framework, we have developed a practical algorithm to simulate quantum circuits using an attention network based on a powerful neural network ansatz responsible for the most recent breakthroughs in natural language processing. We demonstrate our approach by simulating circuits that build Greenberger-Horne-Zeilinger and linear graph states of up to 60 qubits, as well as a variational quantum eigensolver circuit for preparing the ground state of the transverse field Ising model on several system sizes. Our methodology constitutes a modern machine learning approach to the simulation of quantum physics with applicability both to quantum circuits as well as other quantum many-body systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

All-electron, density-functional-based method for angle-resolved tunneling ionization in the adiabatic regime

Here we develop and test a method that integrates many-electron weak-field asymptotic theory (ME-WFAT) [O. I. Tolstikhin, L. B. Madsen, and T. Morishita, Phys. Rev. A 89, 013421 (2014)] in the integral representation (IR) into the density-functional-theory (DFT) framework. In particular, we present modifications of the integral formula in the IR ME-WFAT to incorporate the potential terms unique to DFT. By solving an adiabatic rate equation for the angle-resolved ionization yield in our DFT-based ME-WFAT method, we show that the results are in excellent agreement with those of real-time time-dependent density-functional-theory (TDDFT) simulations for NO, OCS, C⁢H 3 ⁢Br, and C⁢H 3 ⁢Cl interacting with one- and two-color laser fields with a fundamental wavelength of 800 nm. This agreement is significant because the WFAT calculations take only a small fraction of the time of full TDDFT calculations. These results suggest that in the wavelength region commonly used in strong-field experiments (800 nm and longer), our DFT-based WFAT treatment can be used to rapidly screen for the ionization properties of a large number of molecules as a function of alignment or orientation between the molecule and the strong field.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗