Search NASA⌕ Search

SEARCH · Search NASA

Results for “Choi matrix”

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.

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

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

A non-commutative Bayes' theorem

Using a diagrammatic reformulation of Bayes' theorem, we provide a necessary and sufficient condition for the existence of Bayesian inference in the setting of finite-dimensional C* -algebras. In other words, we prove an analogue of Bayes' theorem in the joint classical and quantum context. Our analogue is justified by recent advances in categorical probability theory, which have provided an abstract formulation of the classical Bayes' theorem. In the process, we further develop non-commutative almost everywhere equivalence and illustrate its important role in non-commutative Bayesian inversion. The construction of such Bayesian inverses, when they exist, involves solving a positive semidefinite matrix completion problem for the Choi matrix. This gives a solution to the open problem of constructing Bayesian inversion for completely positive unital maps acting on density matrices that do not have full support. In conclusion, we illustrate how the procedure works for several examples relevant to quantum information theory.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

Classical shadows for quantum process tomography on near-term quantum computers

Quantum process tomography is a powerful tool for understanding quantum channels and characterizing the properties of quantum devices. Inspired by recent advances using classical shadows in quantum state tomography [H.-Y. Huang, R. Kueng, and J. Preskill, .], we have developed ShadowQPT, a classical shadow method for quantum process tomography. We introduce two related formulations with and without ancilla qubits. ShadowQPT stochastically reconstructs the Choi matrix of the device allowing for an classical evaluation of the device on arbitrary inputs with respect to arbitrary outputs. Using shadows, we then show how to compute overlaps, generate all k -weight reduced processes, and perform reconstruction via Hamiltonian learning. These latter two tasks are efficient for large systems as the number of quantum measurements needed scales only logarithmically with the number of qubits. A number of additional approximations and improvements are developed, including the use of a pair-factorized Clifford shadow and a series of postprocessing techniques that significantly enhance the accuracy for recovering the quantum channel. We have implemented ShadowQPT using both Pauli and Clifford measurements on the IonQ trapped ion quantum computer for quantum processes up to n = 4 qubits, and we achieved good performance. Published by the American Physical Society 2024

Levy, Ryan (ORCID:0000000349527156)↗
NASA NTRS2002

Processing and Mechanical Properties of Various Zirconia/Alumina Composites for Fuel Cell Applications

Various electrolyte materials for solid oxide fuel cells were fabricated by hot pressing 10 mol% yttria-stabilized zirconia (10-YSZ) reinforced with two different forms of alumina, particulates and platelets, each containing 0 to 30 mol% alumina. Flexure strength and fracture toughness of both particulate and platelet composites at ambient temperature increased with increasing alumina content, reaching a maximum at 30 mot% alumina. For a given alumina content, strength of particulate composites was greater than that of platelet composites, whereas, the difference in fracture toughness between the two composite systems was negligible. No virtual difference in elastic modulus and density was observed for a given alumina content between particulate and platelet composites. Thermal cycling up to 10 cycles between 200 to 1000 C did not show any effect on strength degradation of the 30 mol% platelet composites, indicative of negligible influence of CTE mismatches between YSZ matrix and alumina grains.

Choi, Sung R.↗
NASA NTRS2008

Impact Resistance of Uncoated SiC/SiC Composites

Two-dimensional woven SiC/SiC composites fabricated by melt infiltration method were impact tested at room temperature and at 1316 C in air using 1.59-mm diameter steel-ball projectiles at velocities ranging from 115 to 400 m/s. The extent of substrate damage with increasing projectile velocity was imaged and analyzed using optical and scanning electron microscopy, and non-destructive evaluation (NDE) methods such as pulsed thermography, and computed tomography. The impacted specimens were tensile tested at room temperature to determine their residual mechanical properties. Results indicate that at 115 m/s projectile velocity, the composite showed no noticeable surface or internal damage and retained its as-fabricated mechanical properties. As the projectile velocity increased above this value, the internal damage increased and mechanical properties degraded: At velocities >300 m/s, the projectile penetrated through the composite, but the composite retained approx.50% of the ultimate tensile strength of the as-fabricated composite and exhibited non-brittle failure. Predominant internal damages are delamination of fiber plies, fiber fracture and matrix shearing.

Bhatt, Ramakrishna T.↗
DOE OSTI2023

Towards quantum black hole microstates

Abstract We study the cohomology of local BPS operators in$$ \mathcal{N} $$ N = 4 Yang-Mills theory. The finiteNcohomologies consist of the graviton part (subject to the stringy exclusion principle) and the rest which may describe black hole microstates in quantum AdS/CFT. We construct an infinite tower of non-graviton cohomologies in the SU(2) theory and study to what extent they simulate quantum black holes. We find signals for partial no-hair behaviors by showing that certain gravitons are forbidden to dress these cohomologies. This is in qualitative agreement with the perturbative hairs allowed around black holes, which also leads us to a natural setup to construct hairy BPS black holes. The cohomologies are simpler to study in the BMN matrix model truncation of the classical field theory.

Physics↗
NASA NTRS1991

Comparison of dynamic fatigue behavior between SiC whisker-reinforced composite and monolithic silicon nitrides

The dynamic fatigue behavior of 30 vol percent silicon nitride whisker-reinforced composite and monolithic silicon nitrides were determined as a function of temperature from 1100 to 1300 C in ambient air. The fatigue susceptibility parameter, n, decreased from 88.1 to 20.1 for the composite material, and from 50.8 to 40.4 for the monolithic, with increasing temperature from 1100 to 1300 C. A transition in the dynamic fatigue curve occurred for the composite material at a low stressing rate of 2 MPa/min at 1300 C, resulting in a very low value of n equals 5.8. Fractographic analysis showed that glassy phases in the slow crack growth region were more pronounced in the composite compared to the monolithic material, implying that SiC whisker addition promotes the formation of glass rich phases at the grain boundaries, thereby enhancing fatigue. These results indicate that SiC whisker addition to Si3 N4 matrix substantially deteriorates fatigue resistance inherent to the matrix base material for this selected material system.

Choi, Sung R.↗
NASA NTRS2001

Narrow band emission from lithographically defined photonic bandgap structures in silicon: matching theory and experiment

The authors previously reported discovery of narrow, thermal emission bands from symmetrically patterned features etched into silicon wafers. In this paper, we report further results that show the measured absorption peaks for such patterned surfaces match theoretical calculations of the complete electrodynamic problem solved using the Transfer Matrix Method (TMM).

photonic↗
NASA NTRS2006

Life Limiting Behavior in Interlaminar Shear of Continuous Fiber-Reinforced Ceramic Matrix Composites at Elevated Temperatures

Interlaminar shear strength of four different fiber-reinforced ceramic matrix composites was determined with doublenotch shear test specimens as a function of test rate at elevated temperatures ranging from 1100 to 1316 C in air. Life limiting behavior, represented as interlaminar shear strength degradation with decreasing test rate, was significant for 2-D crossplied SiC/MAS-5 and 2-D plain-woven C/SiC composites, but insignificant for 2-D plain-woven SiC/SiC and 2-D woven Sylramic (Dow Corning, Midland, Michigan) SiC/SiC composites. A phenomenological, power-law delayed failure model was proposed to account for and to quantify the rate dependency of interlaminar shear strength of the composites. Additional stress rupture testing in interlaminar shear was conducted at elevated temperatures to validate the proposed model. The model was in good agreement with SiC/MAS-5 and C/SiC composites, but in poor to reasonable agreement with Sylramic SiC/SiC. Constant shear stress-rate testing was proposed as a possible means of life prediction testing methodology for ceramic matrix composites subjected to interlaminar shear at elevated temperatures when short lifetimes are expected.

Choi, Sung R.↗
NASA NTRS1992

Strength, toughness and R-curve behaviour of SiC whisker-reinforced composite Si3N4 with reference to monolithic Si3N4

The flexural strength and fracture toughness of 30 vol pct SiC whisker-reinforced Si3N4 material were determined as a function of temperature from 25 to 1400 C in an air environment. It was found that both strength and toughness of the composite material were almost the same as those of the monolithic counterpart. The room-temperature strength was retained up to 1100 C; however, appreciable strength degradation started at 1200 C and reached a maximum at 1400 C due to stable crack growth. In contrast, the fracture toughness of the two materials was independent of temperature with an average value of 5.66 MPa sq rt m. It was also observed that the composite material exhibited no rising R-curve behavior at room temperature, as was the case for the monolithic material. These results indicate that SiC whisker addition to the Si3N4 matrix did not provide any favorable effects on strength, toughness and R-curve behavior.

Choi, S. R.↗
NASA NTRS2005

Boron Nitride Nanotubes-Reinforced Glass Composites

Boron nitride nanotubes of significant lengths were synthesized by reaction of boron with nitrogen. Barium calcium aluminosilicate glass composites reinforced with ~4 weight percent of BN nanotubes were fabricated by hot pressing. Ambient-temperature flexure strength and fracture toughness of the glass-BN nanotube composites were determined. The strength and fracture toughness of the composite were higher by as much as 90 and 35 percent, respectively, than those of the unreinforced glass. Microscopic examination of the composite fracture surfaces showed pullout of the BN nanotubes. The preliminary results on the processing and improvement in mechanical properties of BN nanotube reinforced glass matrix composites are being reported here for the first time.

Bansal, Narottam↗
DOE OSTI2023

High-performance strategies for the recent MRSF-TDDFT in GAMESS

Multiple ERI (Electron Repulsion Integral) tensor contractions (METC) with several matrices are ubiquitous in quantum chemistry. In response theories, the contraction operation, rather than ERI computations, can be the major bottleneck, as its computational demands are proportional to the multiplicatively combined contributions of the number of excited states and the kernel pre-factors. Here, this paper presents several high-performance strategies for METC. Optimal approaches involve either the data layout reformations of interim density and Fock matrices, the introduction of intermediate ERI quartet buffer, and loop-reordering optimization for a higher cache hit rate. The combined strategies remarkably improve the performance of the MRSF (mixed reference spin flip)-TDDFT (time-dependent density functional theory) by nearly 300%. The results of this study are not limited to the MRSF-TDDFT method and can be applied to other METC scenarios.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2005

Solid Oxide Fuel Cell Seal Glass - BN Nanotubes Composites

Solid oxide fuel cell seal glass G18 composites reinforced with approx.4 weight percent of BN nanotubes were fabricated via hot pressing. Room temperature strength and fracture toughness of the composite were determined by four-point flexure and single edge V-notch beam methods, respectively. The strength and fracture toughness of the composite were higher by as much as 90% and 35%, respectively, than those of the glass G18. Microscopic examination of the composite fracture surfaces using SEM and TEM showed pullout of the BN nanotubes, similar in feature to fiber-reinforced ceramic matrix composites with weak interfaces. Other mechanical and physical properties of the composite will also be presented.

Bansal, Narottam P.↗
DOE OSTI2024

Metasurface‐Based Mueller Matrix Microscope

In conventional optical microscopes, image contrast of objects mainly results from the differences in light intensity and/or color. Muller matrix optical microscopes (MMMs), on the other hand, can provide significantly enhanced image contrast and rich information about objects by analyzing their interactions with polarized light. However, state-of-the-art MMMs are fundamentally limited by bulky and slow polarization state generators and analyzers. Here, the study demonstrates a metasurface-based MMM, i.e., Meta-MMM, which is equipped with a chip-integrated, single-shot metasurface polarization state analyzer (Meta-PSA). The Meta-MMM is featured with high-speed measurement (≈2s per Muller matrix (MM) image), superior operation stability, dual-color operation, and high measurement accuracy (measurement error 1–2%) for MM imaging. The Meta-MMM is applied to nanostructure characterization, surface morphology analysis, and discovering birefringent structures in honeybee wings. As a result, the Meta-MMMs hold the promise to revolutionize various applications from biological imaging, medical diagnosis, and material characterization to industry inspection and space exploration.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effective description of sub-maximal chaos: stringy effects for SYK scrambling

It has been proposed that the exponential decay and subsequent power law saturation of out-of-time-order correlation functions can be universally described by collective ‘scramblon’ modes. We develop this idea from a path integral perspective in several examples, thereby establishing a general formalism. After reformulating previous work on the Schwarzian theory and identity conformal blocks in two-dimensional CFTs relevant for systems in the infinite coupling limit with maximal quantum Lyapunov exponent, we focus on theories with sub-maximal chaos: we study the large-q limit of the SYK quantum dot and chain, both of which are amenable to analytical treatment at finite coupling. In both cases we identify the relevant scramblon modes, derive their effective action, and find bilocal vertex functions, thus constructing an effective description of chaos. The final results can be matched in detail to stringy corrections to the gravitational eikonal S-matrix in holographic CFTs, including a stringy Regge trajectory, bulk to boundary propagators, and multi-string effects that are unexplored holographically.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Isolation and spectroscopy of C 2 H + ions in helium droplets

Ethynylium (C 2 H + ) may be an important intermediate in astrochemistrybut remains poorly studied by laboratory techniques due to its high reactivity. Immersion of single acetylene molecules in helium nanodroplets followed by electron impact ionization effectively generates and isolates C 2 H + cations in an inert cryogenic environment, enabling infrared spectroscopic measurements. Here, we find that in the C-H stretching range, the C 2 H + spectrum appears as a triplet with splitting of 33.6 cm —1 and 37.5 cm —1 . The splitting is temporarily assigned to the product of interactions between the C-H stretching mode and overtones of the bending mode.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1987

Response of stiffened panels for applications to acoustic fatigue

The surface protection systems of aerospace and aircraft structures are often constructed from discretely stiffened panels. This paper presents an analytical study on dynamic stress response of these structures to random surface flow and acoustic loads. To account for aerodynamic heating of high speed flow, thermal effects are included in the structural model. A generalized transfer matrix procedure is developed to obtain the required dynamic response solutions. Numerical results include spectral densities of stress, response root mean square values and fatigue damage for a variety of loading and thermal conditions.

Vaicaitis, R.↗
NASA NTRS1993

Processing and testing of high toughness silicon nitride ceramics

High toughness silicon nitride ceramics were processed with the addition of small quantities of beta-Si3N4 whiskers in a commercially available alpha-Si3N4 powder. These whiskers grew preferentially during sintering resulting in large, elongated beta-grains, which acted to toughen the matrix by crack deflection and grain pullout. The fracture toughness of these samples seeded with beta-Si3N4 whiskers ranged from 8.7 to 9.5 MPa m(exp 0.5) depending on the sintering additives.

Tikare, Veena↗