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 & Thin film. The organization has 21501 authors who have published 46724 publications receiving 1484388 citations. The organization is also known as: SNL & Sandia National Labs.

Modular entanglement of atomic qubits using photons and phonons

Abstract: Many quantum protocols require fast, remote entanglement generation to outperform their classical counterparts. A modular solution is now reported, using trapped ions that are remotely entangled through photons. Quantum entanglement is the central resource behind quantum information science, from quantum computation and simulation1,2 to enhanced metrology3 and secure communication1. These applications require the quantum control of large networks of qubits to realize gains and speed increases over conventional devices. However, propagating entanglement becomes difficult or impossible as the system grows in size. Here, we demonstrate the first step in a modular approach4 to scaling entanglement by using complementary quantum buses on a collection of three atomic ion qubits stored in two remote ion trap modules. Entanglement within a module is achieved with deterministic near-field interactions through phonons5, and remote entanglement between modules is achieved with a probabilistic interaction through photons6. This minimal system allows us to address generic issues in the synchronization of entanglement with multiple buses. It points the way towards a modular large-scale quantum information architecture that promises less spectral crowding and thus potentially less decoherence as the number of qubits increases4. We generate this modular entanglement faster than the observed remotely entangled qubit-decoherence rate, showing that entanglement can be scaled simply by adding more modules.

Communication-optimal parallel and sequential QR and LU factorizations

Abstract: We present parallel and sequential dense QR factorization algorithms that are both optimal (up to polylogarithmic factors) in the amount of communication they perform, and just as stable as Householder QR. We prove optimality by extending known lower bounds on communication bandwidth for sequential and parallel matrix multiplication to provide latency lower bounds, and show these bounds apply to the LU and QR decompositions. We not only show that our QR algorithms attain these lower bounds (up to polylogarithmic factors), but that existing LAPACK and ScaLAPACK algorithms perform asymptotically more communication. We also point out recent LU algorithms in the literature that attain at least some of these lower bounds.

Progressive hedging innovations for a class of stochastic mixed-integer resource allocation problems

Abstract: Numerous planning problems can be formulated as multi-stage stochastic programs and many possess key discrete (integer) decision variables in one or more of the stages. Progressive hedging (PH) is a scenario-based decomposition technique that can be leveraged to solve such problems. Originally devised for problems possessing only continuous variables, PH has been successfully applied as a heuristic to solve multi-stage stochastic programs with integer variables. However, a variety of critical issues arise in practice when implementing PH for the discrete case, especially in the context of very difficult or large-scale mixed-integer problems. Failure to address these issues properly results in either non-convergence of the heuristic or unacceptably long run-times. We investigate these issues and describe algorithmic innovations in the context of a broad class of scenario-based resource allocation problem in which decision variables represent resources available at a cost and constraints enforce the need for sufficient combinations of resources. The necessity and efficacy of our techniques is empirically assessed on a two-stage stochastic network flow problem with integer variables in both stages.

Enhancement of X-Ray Power from a Z Pinch Using Nested-Wire Arrays

Abstract: Nested-wire arrays on the 20-MA Z -pinch accelerator have produced x-ray powers up to 280{plus_minus}40 TW (a 40{percent} increase over a single array) and an x-ray pulse width of 4thinspthinspns. The short x-ray pulse widths are associated with the formation of tight (1-mm-diameter), uniform pinches at stagnation. Two-dimensional radiation magnetohydrodynamic calculations suggest that the inner array mitigates the growth of implosion instabilities thereby leading to smaller diameter pinches that radiate at higher power than single-wire arrays. {copyright} {ital 1998} {ital The American Physical Society }

Combustion at the focus: laser diagnostics and control

Abstract: Fifty years after the foundation of the Combustion Institute and almost 150 years after Michael Faraday's famous lectures on the combustion of a candle, combustion diagnostics have come a long way from visual inspection of a flame to detailed analysis of a combustion process with a multitude of sophisticated techniques, often using lasers. The extended knowledge on combustion phenomena gained by application of these diagnostic techniques, combined with equally advanced numerical simulation of the process, has been instrumental in designing modern combustion devices with efficient performance and reduced pollutant emission. Also, similar diagnostic techniques are now employed to develop sensors for process control in combustion. This article intends to give a perspective on the potential of combustion diagnostics by highlighting selected application examples and by guiding the reader to recent literature. In particular, techniques are emphasized, which permit measurement of important features of the chemical composition, sometimes in conjunction with flow field parameters. Although a complete image of present research and applications in combustion diagnostics and control is beyond the scope of this article, this overview may be a starting place where ideas may be found to solve specific combustion problems with the aid of diagnostics. (Less)