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STE Highlights, April 2022

Analytics, Intelligence and Technology

Topological magnon band structure of emergent Landau levels in a skyrmion lattice

The propagation of spin waves perpendicular to skyrmions displays a quantization of the circular orbits. In addition, the circular orbit is topologically non-trivial: It carries a subtle twist, somewhat similar to a so-called Möbius strip.

The propagation of spin waves perpendicular to skyrmions displays a quantization of the circular orbits. In addition, the circular orbit is topologically non-trivial: It carries a subtle twist, somewhat similar to a so-called Möbius strip. Image credit: Christoph Hohmann, Munich Center for Quantum Science and Technology

The magnetic excitations of the skyrmion lattice were theorized to be spatially complex, low in energy and momentum, and have small scattering intensity, requiring specialized high-resolution neutron spectrometers to directly observe and advanced resolution convolution algorithms to analyze.

The magnetic excitations of the skyrmion lattice were theorized to be spatially complex, low in energy and momentum, and have small scattering intensity, requiring specialized high-resolution neutron spectrometers to directly observe and advanced resolution convolution algorithms to analyze.

At low enough temperatures and sufficient applied magnetic fields, the spins in manganese silicide (MnSi) form a so-called skrymion lattice, which is an ordered arrangement of Bloch-type skyrmions with hexagonal symmetry.

At low enough temperatures and sufficient applied magnetic fields, the spins in manganese silicide (MnSi) form a so-called skrymion lattice, which is an ordered arrangement of Bloch-type skyrmions with hexagonal symmetry.

Almost all electronic components used today are based on controlling the movements of electrons. A major drawback to electrical conductors, though, is that resistance to an electrical current generates heat, resulting in substantial energy waste. One potential alternative to electric flow may be found in “magnons,” or travelling magnetic waves, that can transport information without producing waste heat and potentially result in smaller electronic components. For technical applications, it is critical to be able to control the properties of magnetic waves, such as their size and direction of movement. As recently described in Science, an international research team, with significant contributions from Los Alamos National Laboratory experts David M. Fobes (A-1) and Marc Janoschek (formerly MPA-CMMS), has explored the fundamental physics that underpin magnons, potentially representing an important breakthrough for the development of quantum technologies.

In conventional magnets, the magnetic waves generally move in a straight line with a fixed momentum. But in a relatively new class of magnetic materials, the magnetic waves form lattices of vortex tubes known as skyrmions. While existence of skyrmions has been shown experimentally for nearly 15 years, originally discovered by members of this international team, the nature of their magnetic excitations has only been theorized until now. For the first time, researchers have developed a comprehensive theory for the magnons in the skyrmion lattice phase, and directly observed these excitations via neutron spectroscopy. Combining theory and experimentation, researchers have demonstrated that the magnetic waves in a skyrmion lattice move in a circular path, rather than a straight line, and are quantized, which together leads to especially stable motion in the material.

The research uncovers that the motion of a spin excitation across topologically non-trivial magnetic order exhibits a deflection analogous to the effect of the Lorentz force on an electrically charged particle in an orbital magnetic field. The research team investigated the propagation of magnons, i.e., bosonic collective spin excitations, in a lattice of skyrmion tubes in manganese monosilicide (MnSi) using a combination of polarized and unpolarized inelastic neutron scattering. For wavevectors perpendicular to the skyrmion tubes, the magnon spectra are consistent with the formation of finely spaced emergent Landau levels characteristic of the fictitious magnetic field used to account for the non-trivial topological winding of the skyrmion lattice. This provides evidence of a topological magnon band structure in reciprocal space, which is born out of the non-trivial real-space topology of a magnetic order.

Funding and Mission

This work was supported by the German Research Foundation; the European Research Council; the Laboratory Directed Research and Development program at Los Alamos National Laboratory; the Institute for Materials Science at Los Alamos; and resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The work supports the Global Security mission area and the Materials for the Future capability pillar.

Reference

“Topological magnon band structure of emergent Landau levels in a skyrmion lattice,” Science, 375, 6584, 1025 (2022); DOI: 10.1126/science.abe4441. Authors: D. M. Fobes (Los Alamos National Laboratory); T. Weber, M. Böhm, P. Steffens (Institut Laue-Langevin); J. Waizner (University of Cologne); G. S. Tucker (Paul Scherrer Institute, Swiss Federal Institute of Technology in Lausanne); L. Beddrich, C. Franz, H. Gabold, M. Skoulatos, R. Georgii, A. Bauer, C. Pfleiderer, P. Böni (Technical University of Munich); R. Bewley (Rutherford Appleton Laboratory); D. Voneshen (Rutherford Appleton Laboratory, Royal Holloway University of London); G. Ehlers (Oak Ridge National Laboratory); M. Janoschek (Los Alamos National Laboratory, Paul Scherrer Institute, University of Zurich); and M. Garst (University of Cologne, TU Dresden, Karlsruhe Institute of Technology).

Technical Contact: David Fobes

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Chemistry

Controlled potential coulometry for plutonium assay

Upgraded SRNL CPC system in the Laboratory RLUOB in 2019. Los Alamos and SRNL personnel are completing the install and testing the equipment.

Upgraded SRNL CPC system in the Laboratory RLUOB in 2019. Los Alamos and SRNL personnel are completing the install and testing the equipment.

Los Alamos scientist using the newly installed CPC system in RLUOB.

Los Alamos scientist using the newly installed CPC system in RLUOB.

Los Alamos National Laboratory’s Actinide Analytical Chemistry group’s (C-AAC) controlled potential coulometric (CPC) plutonium assay method fills an important role for many programs of both national and international importance. As part of the Department of Energy (DOE) nuclear facilities upgrade process and in support of NNSA’s Plutonium Production Program, C-AAC is moving into new laboratory space at TA-55’s Radiological Laboratory Utility Office Building (RLUOB). In collaboration with Savannah River National Laboratory (SRNL), a new coulometer has been installed and made ready at the new laboratory space at the RLUOB. The new instrument has now begun the qualification and validation process to become war reserve- and ISO17025-certified while software modernization and user interface improvement is ongoing.

The controlled potential coulometric plutonium assay method is a primary tool for material control and accountability and executes work in all of DOE’s missions: national security, science, control and accountability. In addition, CPC assay is used to certify the standards used by DOE programs in defense, nonproliferation and nuclear accountability/safeguards, counter-proliferation, nuclear materials technologies, and basic science. Many non-destructive assay instruments used throughout the DOE complex are calibrated with matrix matched standards that were standardized against assays provided by the CPC method.

Since the early 1970s, Los Alamos had used a custom CPC system implementing PAR 173 technology. In the early 1980s SRNL sought a commercially available CPC system, but could not find one that provided sufficient stability, precision and accuracy to certify plutonium reference standards and meet the needs of plutonium production and research. SRNL met this need by designing and building a custom CPC system. This first-generation SRS coulometer is based on the DOE-NBL coulometer,  developed by the research team of Holland, Frazzini, Weiss and Pietri at what is now the NBL Program Office. This system rapidly gained international recognition and was adopted by several organizations including the International Atomic Energy Agency (IAEA). SRNL developed its first production coulometer in 1985, building on the work at NBL. SRNL built two coulometers for NBL in the mid-1990s that NBL used to certify CRM-126A.

In 2009, the IAEA and SRNL realized that there were no longer parts for the 1980 (model 1) SRNL design, and Los Alamos analysts realized the old PAR173-based system that had been the workhorse of the Plutonium Assay team since the early 1970s also lacked available replacement parts. SRNL, with funding and input from analysts at all three laboratories (SRNL, Los Alamos and the IAEA), embarked on a total redesign and upgrade of the SRNL system. In 2010-2011, the first three systems were installed at SRNL, IAEA and Los Alamos. The system installed at the Los Alamos Chemistry and Metallurgy Research Facility was both ISO17025 certified and war reserve certified and has been in constant use since 2012. The three labs compared results as part of the overall qualification process. Results obtained from the three laboratories agreed within 0.04%, which is within the margin of error for the measurement.

SRNL was contracted to build new coulometers for use in RLUOB. In 2019, SRNL personnel came to Los Alamos, assembled the system, trained analysts and monitored site acceptance testing. In 2021, SRNL returned to assemble a third instrument that had been delivered in 2020. In addition, they performed system checkups and calibrations for the existing Los Alamos systems.  As part of this SRNL visit, method files were updated to analyze plutonium and match the existing qualified Los Alamos instrument.

Funding and Mission

The work is funded by Plutonium Modernization and it supports the Nuclear Deterrence mission area and the Materials for the Future capability pillar.

Technical Contacts: Lisa Colletti, Miller Wylie, Steve Willson

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Nuclear Engineering and Nonproliferation

Special journal issue commemorates NCERC 10-year anniversary

NCERC crew members measure the combined height of fuel and reflector loaded on Comet for a criticality experiment.

NCERC crew members measure the combined height of fuel and reflector loaded on Comet for a criticality experiment.

A special issue of Nuclear Science and Engineering commemorates the 10-year anniversary of the National Criticality Experiments Research Center, operated by Los Alamos National Laboratory for the U.S. Department of Energy National Nuclear Security Administration and located at the Nevada National Security Site. The papers within the issue focus on each of the four critical assemblies at the NCERC as well as the radiation test object measurements.

The papers provide overviews of the operations and experiments conducted with four critical assemblies which previously resided at Technical Area-18 in Los Alamos, New Mexico, as part of the Los Alamos Critical Experiments Facility (LACEF) before relocation to the NCERC. Planet, a vertical-lift assembly machine, is used to perform the Class Foils experiment, which involves stacking highly enriched uranium foils with lucite or polyethylene moderator to demonstrate how the addition of a moderator can produce a critical configuration.  This was the first critical experiment performed on Planet for the startup of NCERC. Comet, another vertical-lift assembly, has hosted experiments including in the Zeus configurations, reflected by copper and focused on intermediate energy spectra.

Two other assemblies are described in the Nuclear Science and Engineering series. The Flattop critical assembly, with interchangeable uranium and plutonium cores started up in 2011. Godiva IV, a fast-burst critical assembly constructed of approximately 65 kg of highly enriched uranium fuel alloyed with 1.5% molybdenum for strength, is one of the last such critical assemblies in the United States and can be used for studies of super-prompt-critical behavior as well as irradiations and demonstrations.

The final paper in the special issue concerns the first 10 years of Radiation Test Object (RTO) operations at NCERC. Built by hand, RTOs are subcritical configurations of special nuclear material. The configurations are useful for benchmark experiments, detector testing and characterization, and training.

The critical assembly machines and RTO operations are used for various training courses for fissionable material handlers and criticality safety engineers throughout the DOE complex to maintain the ability to handle nuclear material safely.

Funding and Mission

The NCERC is funded by the Department of Energy’s Nuclear Criticality Safety Program. The work supports the Global Security mission area and the Nuclear and Particle Futures capability pillar.

References

“A New Era of Nuclear Criticality Experiments: The First 10 Years of Planet Operations at NCERC,” Nuclear Science and Engineering, 195, sup1, S1-S16 (2021). DOI: 10.1080/00295639.2021.1951077. Authors: Rene Sanchez, Theresa Cutler, Joetta Goda, Travis Grove, David Hayes, Jesson Hutchinson, George McKenzie, Alexander McSpaden, William Myers, Roberto Rico, Jessie Walker and Robert Weldon.

“A New Era of Nuclear Criticality Experiments: The First 10 Years of Godiva IV Operations at NCERC,” Nuclear Science and Engineering, 195, sup1, S55-S79 (2021). DOI: 10.1080/00295639.2021.1947103. Authors: Joetta Goda, Caiser Bravo, Theresa Cutler, Travis Grove, David Hayes, Jesson Hutchinson, George McKenzie, Alexander McSpaden, William Myers, Rene Sanchez and Jessie Walker.

“A New Era of Nuclear Criticality Experiments: The First 10 Years of Flattop Operations at NCERC,” Nuclear Science and Engineering, 195, sup1, S37-S54 (2021). DOI: 10.1080/00295639.2021.1947104. Authors: David Hayes, Todd Bredeweg, Theresa Cutler, Joetta Goda, Travis Grove, Jesson Hutchinson, Juliann Lamproe, George McKenzie, Alexander McSpaden, William Myers, Rene Sanchez and Jessie Walker.

“A New Era of Nuclear Criticality Experiments: The First 10 Years of Comet Operations at NCERC,” Nuclear Science and Engineering, 195, sup1, S17-S36 (2021). DOI: 10.1080/00295639.2021.1947105. Authors: Nicholas Thompson, Rene Sanchez, Joetta Goda, Kelsey Amundson, Theresa Cutler, Travis Grove, David Hayes, Jesson Hutchinson, Cole Kostelac, George McKenzie, Alexander McSpaden, William Myers and Jessie Walker.

“A New Era of Nuclear Criticality Experiments: The First 10 Years of Radiation Test Object Operations at NCERC,” Nuclear Science and Engineering, 195, sup1, S80-S98 (2021). DOI: 10.1080/00295639.2021.1918938. Authors: Jesson Hutchinson, John Bounds, Theresa Cutler, Derek Dinwiddie, Joetta Goda, Travis Grove, David Hayes, George McKenzie, Alexander McSpaden, James Miller, William Myers, Ernesto Andres Ordonez Ferrer, Rene Sanchez, Travis Smith, Katrina Stults, Nicholas Thompson and Jessie Walker.

Technical Contact: Joetta Goda

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Physics

ECCE detector design selected for Electron-Ion Collider

The Los Alamos team is testing an advanced silicon sensor, which can be used for part of the EIC instrumentation.

The Los Alamos team is testing an advanced silicon sensor, which can be used for part of the EIC instrumentation.

The Los Alamos team is characterizing the performance of a mini-tracker, which will be upgraded to a full detector subsystem of the future EIC.

The Los Alamos team is characterizing the performance of a mini-tracker, which will be upgraded to a full detector subsystem of the future EIC.

With critical capability areas led by Los Alamos National Laboratory researchers, the Electron-Ion Collider Comprehensive Chromodynamics Experiment (ECCE) consortium has seen its proposal selected as the reference detector design for the Electron-Ion Collider (EIC). The EIC is a new, large-scale particle accelerator facility being built at Brookhaven National Laboratory to explore the strong nuclear force and better understand the proton-neutron microcosm in the atomic nucleus. It has received the Critical Decision 1 approval from the Department of Energy and moves towards detector design and construction. Much like a CT scanner for atoms, the EIC will collide electrons with protons and nuclei to produce snapshots of those particles’ internal structure, including the arrangement of the quarks and gluons that make up the protons and neutrons of nuclei. The strong nuclear force that holds quarks together, carried by the gluons, is the strongest force in nature, and is a major source of power for the world today.

The EIC will be the most powerful electron microscope ever built, offering a combination of versatility, resolving power and intensity. At the EIC, high-energy electrons collide with high-energy protons or a range of different ion (from hydrogen to lead) beams. A number of key science questions will be addressed, including parton mass and spin and interactions; the distribution in momentum and space of partons inside the nucleon; the interaction with a nuclear medium of color-charged quarks and gluons; the process by which confined hadronic states emerge from quarks and gluons; and the method in which quark-gluon interactions create nuclear binding.

The ECCE proposal was selected as the reference design after an extensive review by the Detector Proposal Advisory Panel, jointly commissioned by Brookhaven National Laboratory and Thomas Jefferson National Laboratory. Los Alamos had significant involvement in the ECCE proposal as well as the ATHENA proposal, parts of which has been included in the ECCE detector design. Ivan Vitev, researcher in Los Alamos’ Theoretical division, is principal investigator for the EIC Directed Research Project. Xuan Li is co-principal investigator and co-convener of the ECCE tracking working group. Ping Wong is co-convenor of the ECCE heavy flavor and jet working group. Cameron Dean is the ECCE computing working group co-convener. Los Alamos has also synergized theory and experiment capabilities to contribute unique ideas and innovative developments in Quantum Chromodynamics theory, Electron-Ion Collider phenomenology, and quantum and high-performance computing. Next steps for the EIC project will be to evolve to the formal collaboration formation for the updated detector technical design with contributions across the world ahead of a 2023 DOE Critical Decision 2 review.  

Funding and Mission

This work is supported by the Laboratory Directed Research and Development program. The work supports the Energy Security mission and the Nuclear and Particle Futures capability pillar.

Technical Contact: Xuan Li

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Theoretical

High-quality thermal Gibbs sampling with quantum annealing hardware

This work identified a clear and consistent “sweet spot” for high-quality Gibbs sampling

Using total variation (TV) as a distance metric, this work identified a clear and consistent “sweet spot” for high-quality Gibbs sampling (dark values) around the energy scale of 0.27. Distortions from noise and other hardware effects are indicated by the brightly colored areas. Previous research had only considered the scales of 0.05 and 1.0 and had not observed this sweet spot.

Generating samples from complex probability distributions is the computational crux of many methods in artificial intelligence and physics simulation. One notable example is the task of performing Gibbs sampling when training and utilizing machine learning models called Boltzmann Machines. Although known to be powerful models, Boltzmann Machines are often avoided in practice due to the computational difficulties in sampling. New research published in the journal PR Applied by a Los Alamos National Laboratory team demonstrates for the first time a reliable protocol for performing high-quality Gibbs sampling with quantum annealing hardware. This result opens new opportunities for leveraging Boltzmann Machines in practical applications by utilizing emerging quantum annealing hardware to mitigate the existing computational burdens.

Quantum annealing was originally intended for accelerating the solution of combinatorial optimization tasks that have natural encodings as Ising models, mathematical models of magnetism. However, recent experiments on quantum annealing hardware platforms have demonstrated that, in the operating regime corresponding to weak interactions, the quantum annealing hardware behaves like a noisy Gibbs sampler at a hardware-specific effective temperature.

Building on those previous insights, in this new work, the Laboratory team identified a class of hardware-native Ising models that are robust to noise effects. The team outlined a procedure for executing these models on quantum annealing hardware to maximize Gibbs sampling performance. Experimental results indicate that the proposed protocol results in high-quality Gibbs samples from a hardware-specific effective temperature, which can be adjusted by modulating the annealing time and energy scale. This approach to using quantum annealing hardware for Ising model sampling also presents new opportunities for acceleratingas well as machine learning.

Funding and Mission

This work was supported by the Laboratory Directed Research and Development program. It supports the Global Security mission area and the Information, Science and Technology capability pillar.

Reference

“High-Quality Thermal Gibbs Sampling with Quantum Annealing Hardware,” PR Applied, 17, 044046 (2022). DOI: 10.1103/PhysRevApplied.17.044046. Authors: Jon Nelson, Marc Vuffray, Andrey Lokhov and Carleton Coffrin (Los Alamos National Laboratory); and Tameem Albash (University of New Mexico).

Technical Contact: Andrey Lokhov

Programmable quantum annealers as noisy Gibbs samplers

A single “chimera” cell of a D-Wave quantum annealer

A single “chimera” cell of a D-Wave quantum annealer, with red spurious interactions between qubits that have been discovered in the Los Alamos research.

Writing in the journal PRX Quantum, a team of Los Alamos National Laboratory researchers examined a longstanding question in the search for practical applications of adiabatic quantum computation, a question at the intersection of physics, statistical inference and quantum computing: whether or not physical realizations of quantum annealers can sample from complex high-dimensional probability distributions with a consistent relation to the programmable input. The analysis provided a positive answer to this question, on the way leading to a surprising discovery of spurious interactions between qubits.

Adiabatic quantum computation is a physical principle proposed for finding solutions to hard optimization problems. However, due to environmental noise and thermalization effects, available physical realizations of quantum annealers do not consistently output the optimal solutions, but instead act as samplers from an unknown distribution.

The team studied the sampling properties of quantum annealers implemented through programmable lattices of superconducting flux qubits. Comprehensive statistical analysis of the data produced by these quantum machines showed that these quantum annealers behave as samplers that generate independent configurations from low-temperature, noisy Gibbs distributions.

The structure of the output distribution probes the intrinsic physical properties of the quantum device, such as effective temperature of individual qubits and magnitude of local qubit noise, resulting in a nonlinear response function and spurious interactions that are absent in the hardware implementation. The team proposed an explanation of this new effect by linking spurious interactions to the qubit noise.

The team’s approach has potentially transformative implications for the field of computation, opening up research avenues for developing hardware-accelerated sampling algorithms that will benefit established computational methods. Predictions from this quantitative model have a surprising agreement with experimental data, based on 9 billion quantum annealing runs (representing approximately $1 million in compute time) from eight distinct Quantum Annealing machines developed by D-Wave systems spanning three generations of quantum annealing hardware. With these results, the methodology may gain widespread use in the characterization of future generations of quantum annealers and other emerging analog computing devices.

Funding and Mission

The work was supported by the Laboratory Directed Research and Development Exploratory Research and Early Career Research programs. The work supports the Global Security mission and the Information, Science and Technology capability pillar.

Reference

“Programmable Quantum Annealers as Noisy Gibbs Samplers,” PRX Quantum, 3, 020317 (2022). DOI: 10.1103/PRXQuantum.3.020317. Authors: Marc Vuffray, Carleton Coffrin, Andrey Y. Lokhov (Los Alamos National Laboratory); Yaroslav A. Kharkov (National Institute of Standards and Technology/University of Maryland, College Park).

Technical Contact: Andrey Lokhov

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