Sandia National Laboratories

About: Sandia National Laboratories is a facility organization based out in Livermore, California, United States. It is known for research contribution in the topics: Laser & Combustion. The organization has 21501 authors who have published 46724 publications receiving 1484388 citations. The organization is also known as: SNL & Sandia National Labs.

Graphene Islands on Cu Foils: The Interplay between Shape, Orientation, and Defects

Abstract: We have observed the growth of monolayer graphene on Cu foils using low-energy electron microscopy. On the (100)-textured surface of the foils, four-lobed, 4-fold-symmetric islands nucleate and grow. The graphene in each of the four lobes has a different crystallographic alignment with respect to the underlying Cu substrate. These “polycrystalline” islands arise from complex heterogeneous nucleation events at surface imperfections. The shape evolution of the lobes is well explained by an angularly dependent growth velocity. Well-ordered graphene forms only above ∼790 °C. Sublimation-induced motion of Cu steps during growth at this temperature creates a rough surface, where large Cu mounds form under the graphene islands. Strategies for improving the quality of monolayer graphene grown on Cu foils must address these fundamental defect-generating processes.

Computer-attack graph generation tool

Abstract: This paper presents a tool for assessment of security attributes and vulnerabilities in computer networks. The tool generates attack graphs (Phillips and Swiler, 1998). Each node in the attack graph represents a possible attack state. Edges represent a change of state caused by a single action taken by the attacker or unwitting assistant, and are weighted by some metric (such as attacker effort or time to succeed). Generation of the attack graph requires algorithms that match information about attack requirements (specified in attack templates) to information about the network configuration and assumed attacker capabilities (attacker profile). The set of near-optimal shortest paths indicates the most exploitable components of the system configuration. This paper presents the status of the tool and discusses implementation issues, especially focusing on the data input needs and methods for eliminating redundant paths and nodes in the graph.

Demonstration of qubit operations below a rigorous fault tolerance threshold with gate set tomography

Abstract: Quantum information processors promise fast algorithms for problems inaccessible to classical computers. But since qubits are noisy and error-prone, they will depend on fault-tolerant quantum error correction (FTQEC) to compute reliably. Quantum error correction can protect against general noise if—and only if—the error in each physical qubit operation is smaller than a certain threshold. The threshold for general errors is quantified by their diamond norm. Until now, qubits have been assessed primarily by randomized benchmarking, which reports a different error rate that is not sensitive to all errors, and cannot be compared directly to diamond norm thresholds. Here we use gate set tomography to completely characterize operations on a trapped-Yb+-ion qubit and demonstrate with greater than 95% confidence that they satisfy a rigorous threshold for FTQEC (diamond norm ≤6.7 × 10−4). Quantum computation will depend on fault-tolerant error correction, which requires the chance for errors to occur to be below a certain threshold. Here the authors use gate set tomography as a means to rigorously characterize error rates of single-qubit operations of a qubit encoded in a trapped ion.

Pattern recognition and reading by machine

Abstract: Many efforts have been made to discriminate, categorize, and quantitate patterns, and to reduce them into a usable machine language. The results have ordinarily been methods or devices with a high degree of specificity. For example, some devices require a special type font; others can read only one type font; still others require magnetic ink.