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Los Alamos National Laboratory

Los Alamos National Laboratory

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STE Highlights, June 2020

Awards and Recognition

Hoffman wins DOE Early Career Research Award

Matthew Hoffman

Matthew Hoffman

Matthew Hoffman, of the Fluid Dynamics and Solid Mechanics Group (T-3), received a highly valued Early Career Research Program funding award from the Department of Energy’s Office of Science. This is the 11th year DOE has provided the awards, designed to bolster the nation’s scientific workforce with support to exceptional researchers during their early careers.

“We are committed to supporting our early-career scientists at the Laboratory. Their contributions are essential to continuing our proud tradition of excellence,” said Director Thom Mason. “Matthew’s award reflects the important science our young researchers are doing for both the Laboratory, its mission, and the nation.”

Hoffman’s winning proposal, “Creating a Sea-Level-Enabled E3SM: A Critical Capability for Predicting Coastal Impacts,” creates a regional sea level modeling capability within the Energy Exascale Earth System Model (E3SM). Hoffman’s proposal is the fourth LANL early career project to be awarded since 2009 through the Office of Biological and Environmental Research’s Earth and Environmental Sciences Division at the Office of Science.

“We’re proud of Matt and his accomplishments. His research is an important piece of the E3SM because it fills a critical gap for predicting regional sea-level rise and its impact on the environment, communities and infrastructure along the U.S. coastline,” said Marianne Francois, Theoretical (T) Division Leader. “Matt’s research will account for the interactions between the ocean, ice sheets, and solid Earth and lead to a new model for regional sea-level rise in E3SM.”

Hoffman is a member of the LANL climate modeling team. The modeling team is responsible for the ocean and ice model components of E3SM, DOE’s flagship Earth system model, and studies Earth’s complex water cycle, cryosphere and biogeochemical systems. E3SM is a multi-laboratory project supported by the Office of Biological and Environmental Research in the DOE’s Office of Science.

Current Earth system models are not able to predict regional sea-level change that can greatly vary from region to region, with some areas seeing higher surge than others. Hoffman’s unique modeling tool will be used to quantify the role of regional sea level in future storm surge off the U.S. coast. These first fully consistent regional sea level projections from an Earth system model will be used to investigate the accuracy of existing methods that rely on adding disparate, non-interacting contributions to sea level. The sea-level-enabled E3SM provides a critical missing link required for making actionable projections of coastal impacts with E3SM. The project provides the DOE with a tool for predicting regional sea level targeted to agency needs.

About Hoffman

After receiving undergraduate and master’s degrees in civil and environmental engineering, Hoffman earned his doctorate in environmental sciences and resources with an emphasis in geology from Portland State University. There he studied melting of glaciers in the McMurdo Dry Valleys of Antarctica. He then worked as a research associate at NASA Goddard Space Flight Center, conducting field research on meltwater-induced acceleration of the Greenland Ice Sheet. He joined the Laboratory as a postdoctoral researcher in 2011 and became a technical staff member in the Fluid Dynamics and Solid Mechanics Group in 2014.

Hoffman investigates interactions between ice sheets, the ocean, and the broader climate system and resulting impacts on sea level and is a lead contributor to ice sheet and Earth system models developed at the Laboratory and DOE. He received a 2015 Laboratory Directed Research and Development (LDRD) Early Career Researcher Award for his work on connections between subglacial hydrology and glacier flow. Hoffman has regularly taught at summer schools for glaciology and Earth system modeling and has served on the Earth Systems Review Board for the Laboratory’s Center for Space and Earth Science and as a team lead for the Cryospheric Climate Change sub-area working group contributing to the National Earth Observing Assessment 2016.

About the DOE Early Career Research Program Award

For the 2020 award program, DOE selected 76 scientists from across the nation, including 26 from DOE’s national laboratories and 50 from U.S. universities. Under the program, researchers based at DOE national laboratories will receive grants of $500,000 per year. The research grants are planned for five years and will cover salary and research expenses.

To be eligible for the DOE award, a researcher must be an untenured, tenure-track assistant, or associate professor at a U.S. academic institution or a full-time employee at a DOE national laboratory, who received a Ph.D. within the past 10 years. Research topics are required to fall within one of the DOE Office of Science's six major program offices.

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Maginot elected to American Nuclear Society’s Executive Board

Peter Maginot

Peter Maginot

Peter Maginot, of the Eulerian Codes Group (XCP-2), was recently elected to the American Nuclear Society's (ANS) Mathematics and Computation Division Executive Board for a three-year term. ANS is a premier international society committed to advancing, fostering, and promoting the development and application of nuclear sciences and technologies to benefit society.

Maginot received his Ph.D. in nuclear engineering in 2015 and joined the Laboratory in 2018. He currently develops computational simulation tools needed to model highly coupled multiphysics problems within Eulerian frameworks.

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AGU recognizes Stauffer for excellence in refereeing

Philip Stauffer

Philip Stauffer

Philip Stauffer, of Computational Earth Science Group (EES-16), was awarded the 2019 Editor’s Citation for Excellence in Refereeing by the American Geophysical Union (AGU). AGU is the world’s largest organization of earth and space scientists, with 130,000 members.

Stauffer, who has been a staff research scientist at Los Alamos since 2000, was cited for his conscientious review of articles submitted to AGU’s journal Geophysical Research Letters. His particularly commendable peer review efforts help maintain a high-quality standard in AGU literature.

Stauffer brings extensive experience in hydrogeology, porous flow models, and CO2 sequestration. Some of his notable work on the U.S. nuclear fuel cycle can be found at https://sfwd.lanl.gov/. Dr. Harihar Rajaram of John’s Hopkins University nominated Stauffer for the award.

“I encourage all LANL scientists to carve time out of their busy schedules to serve as reviewers for journals, as we all rely on such reviews to ensure high quality in scientific publications,” Stauffer said.

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Chemistry

Researchers identify chemical signatures using the Earth’s magnetic field

The experimental high-field NMR spectra (9.4 T, top) and the low-field J-coupled spectra (JCS) (50 T, bottom) of 1,2,4,5-tetrafluorobenzene for both the 19F (left) and 1H (right) portions of the spectra. The JCS provides more peaks in both the 19F and 1H spectra, which in turn, increases the information that can be learned about the structure and connectivity of the molecule.

The experimental high-field NMR spectra (9.4 T, top) and the low-field J-coupled spectra (JCS) (bottom) of 1,2,4,5-tetrafluorobenzene for both the F (left) and H (right) portions of the spectra. The JCS provides more peaks in both the F and H spectra, which in turn, increases the information that can be learned about the structure and connectivity of the molecule.

Imagine using the Earth's magnetic field for routine magnetic resonance imaging (MRI) or nuclear magnetic resonance (NMR) spectroscopy to identify chemical signatures. This concept is not as farfetched as it sounds and has recently been brought to fruition by Los Alamos scientists in the LANL Chemistry, Bioscience, Materials Physics and Applications, and Engineering Technology and Design divisions.

The Los Alamos researchers harnessed the Earth’s magnetic field (around 50 microtesla) to generate spectra that identify chemicals, many of which directly impact national security. This methodology was benchmarked by fluorobenzene compounds in a recent foundational publication.

This technique is in stark contrast to the canonical NMR spectroscopy instruments that require costly cryogens and large superconducting magnets. Using the Earth's magnetic field reduces cost and increases portability, but the challenge these researchers had to overcome was the inherent loss of signal concomitant with using a low magnetic field.

J-coupling

The researchers turned to J-coupling, a little-investigated spectral signature phenomenon at Earth’s magnetic field, with simultaneous excitation and detection of 19F and 1H for the analysis of small molecules. Simultaneous measurements cannot be accomplished with conventional NMR. At a low magnetic field (i.e., the Earth’s magnetic field), the strong heteronuclear J-coupling condition is satisfied because J-couplings are magnetic-field independent, allowing the unique peak splitting patterns to be observed. These patterns are unique to low magnetic fields and are not seen in traditional high-field NMR.

Derrick Kaseman is shown here with the instrumentation. Measurements are made by pre-polarizing the sample in a secondary permanent magnetic field to boost signal intensity and rapidly moving the sample (in less than one second) to the Earth’s magnetic field for detection.

Derrick Kaseman is shown here with the instrumentation. Measurements are made by pre-polarizing the sample in a secondary permanent magnetic field to boost signal intensity and rapidly moving the sample (in less than one second) to the Earth’s magnetic field for detection.

Their results were extremely positive. Not only did the J-coupling allow for clear and specific spectra, it also provided quantitative results: pseudo-empirical formulas or relative concentrations. In fact, the chemical information obtained using Earth’s magnetic field from these experiments exceeded that from commercial NMR spectrometers with magnetic fields hundreds of thousands of times higher. Gaining better and more chemical information via spectra is critical to accuracy, reducing the likelihood of false-positive or false-negative identifications. This supports the robust nature of their technique.

Protecting the public

With this Los Alamos-developed technique, a variety of small molecules can be detected and differentiated. Insecticides, pesticides, and chemical nerve agents are examples of the compounds these researchers can currently detect. However, the team continues to develop methods and instrumentation that further overcome sensitivity issues as well as gain a deeper understanding of the spectroscopic rules that govern at these low magnetic fields. This future research will help expand the range of molecules that can be detected at low magnetic fields, including synthetic opioids, pharmaceuticals, and explosives.  

Funding and mission

This research was funded by two Laboratory Directed Research and Development (LDRD) projects as well as a Director’s Fellowship. The work supports the Laboratory’s Global Security mission area and the Science of Signatures capability pillar.

Reference: Derrick C. Kaseman, Michael T. Janicke, Rachel K. Frankle, Tammie Nelson, Gary Angles-Tamayo, Rami J. Batrice, Per E. Magnelind, Michelle A. Espy, and Robert F. Williams. “Chemical Analysis of Fluorobenzenes via Multinuclear Detection in the Strong Heteronuclear J-Coupling Regime.” Appl. Sci. 2020, 10(11), 3836; https://doi.org/10.3390/app10113836

Technical contacts: Derrick Kaseman and Mike Janicke

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Intelligence and Space Research

Los Alamos software discovers new world-record lightning flashes

Not all lightning strikes down from a cloud to the ground. In fact, most lightning flashes occur within a thundercloud, extending horizontally across a storm. Under the right conditions, these horizontal cloud flashes can spread over exceptional distances, but just how far they can go hasn’t been well understood, until now.

Using Los Alamos software developed by Michael Peterson, of Space and Remote Sensing (ISR-2), two “megaflashes” were discovered and deemed world records—one for flash distance and the other for flash duration—by the World Meteorological Organization.

Linear representations of the new record-setting megaflashes.

Linear representations of the new record-setting megaflashes.

The world record for flash distance went to a single horizontal megaflash that occurred over southern Brazil on Oct. 31, 2018. The flash spanned 709 km (440 miles), more than doubling the previous record of 321 km (199 mi). Rather than propagating in one direction from one end to the other, the flash started centrally and extended simultaneously in two directions, northwest and southeast. The flash was finished in 11.3 seconds—easily missed by the population below but forever recorded by space technology.

The other world record was set for a lightning flash duration. It occurred over northern Argentina on March 4, 2019. Although smaller than the Brazil flash, the Argentina flash lasted for over 16.7 seconds, more than twice the duration of the previous record of 7.74 seconds.

“These megaflashes represent atmospheric extremes, which are essential to monitoring climate change as well as safety for both humans on Earth and satellites in space,” Peterson said.

(Top) A plot of the world-record single stratiform lightning flash that covered a distance of 709 km (440 miles) over Brazil. (Bottom) A plot of the world-record duration for a single lightning flash that lasted 16.7 seconds over northern Argentina.

(Top) A plot of the world-record single stratiform lightning flash that covered a distance of 709 km (440 miles) over Brazil. (Bottom) A plot of the world-record duration for a single lightning flash that lasted 16.7 seconds over northern Argentina.

Data analysis after the fact

Although these megaflashes occurred in 2018 and 2019, the full details of their distance and duration weren’t understood until more recently. It took a new type of software and data analysis to fully elucidate the findings.

Peterson developed an analysis technique to repair data recorded by Geostationary Lightning Mapper (GLM) satellites. The GLMs deal with a huge amount of data, and as such, they defer to algorithms that gate recordings to three seconds, artificially splitting megaflashes into several smaller flashes. Peterson’s technique corrects this false splitting.

For the world record, Peterson reprocessed operational GLM data hosted by the National Oceanic and Atmospheric Association at their Comprehensive Large Array-data Stewardship System (CLASS).

With this new analysis technique and modern satellite technology, more discoveries are sure to follow, including national security-relevant discoveries.

Funding and mission

This research was supported in part by NASA, the National Oceanic and Atmospheric Association, and the National Science Foundation. The research supports the Laboratory’s Global Security mission area and the Integrating Information, Science, and Technology for Prediction capability pillar.

References: Michael J. Peterson, Timothy J. Lang (NASA Marshall Space Flight Center), Eric C. Bruning (Texas Tech), Rachel Albrecht (Universidade da São, Brazil), Richard J. Blakeslee, Walter A. Lyons (FMA Research, Colorado), Stéphane Pédeboy (Météorage, Pau France), William Rison (New Mexico Tech), Yijun Zhang (Fudan University, China), Manola Brunet (University Rovira i Virgili), Randall S. Cerveny (Arizona State University). “New WMO Megaflash Lightning Extremes for Flash Distance (709 km) and Duration (16.73 seconds) recorded from Space.” AGU Advances. June 2020. https://doi.org/10.1029/2020GL088888

Michael J. Peterson. “Research Applications for the Geostationary Lightning Mapper Operational Lightning Flash Data Product.” Journal of Geophysical Research: Atmospheres. 2019. https://doi.org/10.1029/2019JD031054

Technical contact: Michael Peterson

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Materials Physics and Applications

New electrochemical hydrogen contamination detector enables widespread use of clean energy

Through a partnership with H2 Frontier and Skyre, Los Alamos researchers developed an affordable technology designed to protect hydrogen fuel cell zero-emission power plant technology from poisoning.

The electrochemical hydrogen contamination detector (HCD) continuously samples hydrogen fuel being dispensed at fueling stations and alerts the station operator when contaminants are detected. The operator can then suspend further refueling before any damage to a vehicle’s fuel cell stack can occur.

The first pre-commercial electrochemical HCD system developed under the DOE Technology Commercialization Fund ready for field testing at a hydrogen filling station.

The first pre-commercial electrochemical HCD system developed under the DOE Technology Commercialization Fund ready for field testing at a hydrogen filling station.

“Our technology acts like a canary in a coal mine,” said Eric Brosha, principal investigator, with Materials Synthesis and Integrated Devices (MPA-11).

Brosha is referring to the fact that the working electrode of the HCD will be poisoned instead of the potentially thousands of expensive fuel cell stacks. The technology simultaneously protects fuel quality and consumer investments.

“Hydrogen fuel cells offer clean and sustainable energy for cars, shipping and delivery vehicles, forklifts, and even critical emergency back-up power,” Brosha said.

With water vapor as the only emission, hydrogen fuel cells are poised to remove human dependence on oil and traditional combustion engines, which produce greenhouse gases.

Inner workings of HCD

The HCD technology is a simple electrochemical hydrogen pump and a working electrode with an ultra-low loaded platinum catalyst and a unique internal water humidification system that permits direct sampling of dry streams of hydrogen fuel. It is based on the same technology as hydrogen fuel cells themselves—perfectly emulating that which they are trying to protect. It is symbolically a canary, but the HCD can be readily regenerated in seconds using basic electrochemical principles.

Hydrogen fuel cells use platinum catalyst particles supported on carbon nanoparticles to split hydrogen (the fuel) and oxygen (the oxidizer) before being electrochemically combined to form water and electricity. Continuous exposure to even low levels of contaminants, such as carbon monoxide, in the hydrogen fuel will interfere with hydrogen adsorption and dissociation, causing a gradual decline in power output from the fuel cell. High concentrations can reduce the power to negligible output in minutes.

The HCD detects those contaminants in near real time, so as the instant fuel quality is compromised, fuel dispensing can be stopped.

Until now, detecting those contaminants has been a challenge. Present detection systems in use are based on analytical laboratory technologies, which are expensive, require high levels of maintenance, or are not sensitive enough for continuous real-time monitoring. The new electrochemical HCD is a game changer for clean energy.

Funding and mission

The research was funded by a DOE Technology Commercialization Fund and the DOE Fuel Cell Technologies Office (FCTO) through the Safety Codes and Standards sub-program. The work supports the Laboratory’s Energy Security mission area and the Complex Natural and Engineered Systems capability pillar.

Reference: E. L. Brosha, T. Rockward, C. J. Romero, M. S. Wilson, C. R. Kreller, and R. Mukundan. “Hydrogen Fuel Quality Analyzer with Self-Humidifying Electrochemical Cell and Method of Testing Fuel Quality.” U. S. Patent No. 10,490,833.

Technical contact: Eric Brosha

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Nuclear Engineering and Nonproliferation

Special issue of Nuclear Technology journal dedicated to KRUSTY test

An entire issue of Nuclear Technology journal has been dedicated to the design work and results of the Kilowatt Reactor Using Sterling TechnologY (KRUSTY) test.

KRUSTY was the culmination of the National Aeronautics and Space Administration (NASA) Kilopower Project to design, build, and test a space nuclear reactor. This test was the first such test since the end of the Space Nuclear Auxiliary Power (SNAP) project at the end of the 1960s.

Design for the 10-kWe fission generator, which is for deep space missions (left), and the 1-kWe kilopower concept (right).

Design for the 10-kWe fission generator, which is for deep space missions (left), and the 1-kWe kilopower concept (right).

Los Alamos National Laboratory scientist Patrick McClure, of the Systems Design and Analysis Group (NEN-5), wrote the forward to the special issue, which has eight peer-reviewed technical articles on various aspects of the KRUSTY test, which has received many accolades.

The Laboratory—in conjunction with the National Aeronautics and Space Administration (NASA) and the Department of Energy—conducted numerous experiments to test the Kilopower system, a fission reaction power system designed at Los Alamos in conjunction with NASA. Designed to provide between 1 and 10 kilowatts of power, Kilopower can work in harsh environments, such as space, and is efficient, reliable, safe, low cost, and compact.

The KRUSTY test successfully demonstrated the efficiency of Kilopower fission power for lunar and planetary exploration. It is anticipated this new nuclear power system could enable long-duration crewed missions to the Moon, Mars, and destinations beyond.

“Kilopower was intended to serve both human exploration needs on planetary surfaces as well as science needs for deep-space exploration,” McClure said.

From reactor design to high-temp experiment

The technical articles move through the design, development, and progressive testing of KRUSTY. As a fission reactor, KRUSTY was the first nuclear-powered operation of any truly new reactor concept in the United States in more than 40 years.

Nuclear testing at the National Criticality Experiments Research Center (NCERC).

Nuclear testing at the National Criticality Experiments Research Center (NCERC).

Kilopower was progressively tested in space-like environments to ensure it would operate as predicted. The final test that proved KRUSTY’s abilities took place in March 2018 over 28 consecutive hours. During the final test, the thermal power ranged from 1.5 to 5.0 kW (thermal), with a fuel temperature up to 880°C. Each 80-W (electric)–rated Stirling converter produced ~90 W (electric) at a component efficiency of ~35% and an overall system efficiency of ~25%. The testing showed that the system operated as expected, and KRUSTY is highly tolerant of possible failure conditions and transients.

Ready for liftoff

Kilopower is poised to power outposts on the Moon and Mars. Where more power is needed, multiple Kilopower units could be deployed.

The safety of the system is based on its innovative structure and physics. The heat-pipe design, with no moving parts in the core, and the self-regulating physics contribute to Kilopower’s large safety margin. Kilopower uses less than five curies of naturally occurring radioactivity. The reactor activates once it reaches its destination (in deep space, on another planet, or in high orbit).

Funding and mission

The project was jointly funded by the Space Technology Mission Directorate at NASA and the Criticality Safety Program at the National Nuclear Security Administration (NNSA). The research supports the Laboratory’s Energy Security mission area and the Nuclear and Particle Futures and Complex Natural and Engineered Systems capability pillars.

Technical contact: Patrick McClure

Reference: Special issue on the Kilopower Project, Kilowatt Reactor Using Sterling TechnologY (KRUSTY) Test. Nuclear Technology. Volume 206, 2020. https://www.tandfonline.com/doi/full/10.1080/00295450.2020.1737486

NASA KRUSTY: https://www.nasa.gov/directorates/spacetech/kilopower

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Theoretical

Metal halide perovskites: Out of the lab, into the consumer market

Metal halide perovskites (MHPs) are a next-generation class of materials touted for their outstanding optoelectronic properties. Excitement has grown for their potential use in photovoltaic technologies (such as solar cells), optoelectronic applications (such as traffic lights and LEDs), and x-ray or gamma-ray detector technologies. But a knowledge gap remains in understanding the charge carrier transport in these complex materials underpinning all these exciting applications.

Bridging this knowledge gap is necessary to moving these new, active-layer MHPs beyond the lab-scale and into the consumer market. The most detailed perspective on MHP charge carrier transport was recently authored by Los Alamos researchers in collaboration with Texas State University and published as the cover feature of The Journal of Physical Chemistry Letters.

Small polaron modeling in MHPs

Small polaron modeling in MHPs

 “The extraordinary photoactivity of these MHP materials is often attributed to their unusually long charge-carrier recombination time,” said Sergei Tretiak of the Physics and Chemistry of Materials group. “It’s important that we understand the physical mechanisms of charge carrier transport in order to optimize these materials.”

Formation of polarons is common thread

The perspective discusses three of the most extensively studied lattice interactions that affect carrier dynamics: electron–phonon scattering limited dynamics, ferroelectric effects, and Rashba-type band splitting. The authors find a common thread among mechanisms, the formation of polarons. A polaron is a quasiparticle formed in highly polarizable solids, such as MHPs.

The researchers found that MHP carrier transport can be rationalized as polaron dynamics, which is an edgy perspective, but one they support with strong evidence. Both large and small polarons were considered, with the authors discussing their formation and effect on structural and carrier dynamics in MHPs.

Some of the evidence the authors pointed to include experimental Raman spectroscopy work that along with computer simulations identifies lattice distortion due to small polaron formation and electron–phonon coupling in the ionic lattices and dominant presence of long-range Coulomb potentials, indicating large polarons to be a dominant carrier charge.

The authors also outlined different physical and chemical approaches considered recently to study and further exploit polaron transport in MHPs.

The in-depth perspective on halide perovskite charge carrier transport was featured on the May cover of The Journal of Physical Chemistry Letters.

The in-depth perspective on halide perovskite charge carrier transport was featured on the May cover of The Journal of Physical Chemistry Letters.

Benefits of MHPs

MHP materials offer a promising alternative to more expensive semiconductor-based devices. MHPs come from inexpensive precursors and offer relatively easy room-temperature fabrication. At the same time, MHPs offer desirable properties.

Thus far, research has shown MHPs offer greater than 24% power conversion efficiency, which is a 10% increase over the last five years alone. What has held this class of materials back is the dearth of knowledge in carrier transport. Therefore, this perspective article will aid in the strategic development of MPH-based technology.

Funding and mission

The research was supported by a Laboratory Directed Research and Development (LDRD) award. This work was done in part at the Center for Nonlinear Studies (CNLS) and the Center for Integrated Nanotechnologies (CINT), a U.S. Department of Energy and Office of Basic Energy Sciences user facility, at LANL. This research used resources provided by the LANL Institutional Computing Program. The research supports the Laboratory’s Energy Security mission area and the Materials for the Future capability pillar.

Reference: D. Ghosh, E. Welch (Texas State University), A. J. Neukirch, A. Zakhidov (Texas State University), and S. Tretiak. “Polarons in Halide Perovskites: A Perspective.” The Journal of Physical Chemistry Letters. May 2020. https://doi.org/10.1021/acs.jpclett.0c00018

Technical contact: Sergei Tretiak

Enhancing gate-based quantum computing methods with hybrid algorithms

Gate-based quantum computers are fully universal, able to run any quantum algorithm. This could offer invaluable knowledge for chemical modeling and advanced materials as well as many other national security applications. However, the state of the current technology is noisy and error-prone, even the top-quality IBM and Google quantum computers suffer from this obstacle.
A schematic of a variational hybrid algorithm that employs both quantum and classical hardware.

A schematic of a variational hybrid algorithm that employs both quantum and classical hardware.

Researchers in the Lab’s Theoretical (T) Division took that seemingly impossible challenge of too much noise and came up with a clever solution: outsourcing some of the noise-causing tasks to a classical computer. The result was a variety of hybrid algorithms that offer quantum-quality speed and classical-quality solutions. The first two of the hybrid algorithms were published in Nature partner journal: quantum information, with several more studies following soon after.

“Quantum resources are precious,” said Lukasz Cincio of the Physics of Condensed Matter and Complex Systems Group (T-4) and winner of the recent IBM Quantum Experience. “We consider which tasks must run on a quantum computer, and the remaining tasks can therefore run on a classical computer. Dividing the labor in this way reduces the quantum circuit depth, which reduces the noise and solution error.”

Circuit length impacts noise

A quantum circuit offers instructions for how to compute. Like a score of music, a circuit has denoted intervals (called gates), with time progressing from left to right. At each gate, an operation is performed, and the circuit must go through these gates in sequential order to reach the end of the “score.” This is unlike an electrical circuit in which a closed loop is followed.

The key to the hybrid algorithm has to do with the gates. Specifically, the aim is to reduce the number of gates (which corresponds to the circuit depth) that run on the quantum computer because that is the source of the noise. Until quantum computers can offer higher-quality, logical qubits for computing, noise will continue to be a limiting factor.

These researchers took various deep circuits—that when run completely on a quantum computer offer unreliable, high-error results—and reduced the depth of the circuits by running some tasks on a classical computer. Their resulting “shallower” circuits of hybrid algorithms offered trustworthy and valuable quantum solutions.

“Classical algorithms have been optimized to run these types of tasks for decades,” Cincio said. Harnessing that reliability for quantum computing was a clever and valuable move—one that enables the Laboratory to utilize current quantum computing technology to its fullest.

Reducing quantum resources and mitigating errors

The team proposed and applied a Variational Fast Forwarding (VFF) approach that dramatically reduces the quantum resources required for simulation. The quality of a quantum simulation quickly decreases with simulation time, as the noise continues to affect the operations. The researchers demonstrated their VFF algorithm increases the “useful” simulation time by a factor of 30. As a result, the VFF algorithm enables the study of previously inaccessible systems.

Hybrid algorithms reduce the effects of noise that accumulate during the computation; however, no matter how shallow the circuit, the noise is always present and alters the results in some way. That is why the researchers introduced a novel data-driven method for mitigating the remaining errors. Their method “learns” to correct the errors by using a training data set, in a method usually applied in machine learning. Their mitigation method goes well beyond current state-of-the art techniques, allowing the correction of much more complex quantum computation. The researchers demonstrated their approach reduces the error by an order of magnitude on a 16-qubit IBM quantum computer and a 64-qubit simulator.

These hybrid algorithms will still be important in the future, when qubits are better and quantum computing is more reliable. They will extend the abilities of quantum computers, allowing researchers to tackle even bigger and more complex problems.

Funding and mission

This work was supported by a Laboratory Directed Research and Development (LDRD) award and by the U.S. DOE, Office of Science, Office of Advanced Scientific Computing Research. The work supports the Laboratory’s Nuclear Deterrence mission area and the Integrating Information, Science, and Technology for Prediction capability pillar.

References:

Ryan LaRose, Arkin Tikku, Etude O’Neel-Judy, Lukasz Cincio, and Patrick Coles. “Variational quantum state diagonalization.” Nature partner journal: quantum information. June 2019. https://www.nature.com/articles/s41534-019-0167-6

Carlos Bravo-Prieto, Ryan LaRose, M. Cerezo, Yigit Subasi, Lukasz Cincio, and Patrick J. Coles. “Variational Quantum Linear Solver: A Hybrid Algorithm for Linear Systems.” https://arxiv.org/abs/1909.05820

Cristina Cirstoiu, Zoe Holmes, Joseph Iosue, Lukasz Cincio, Patrick J. Coles, and Andrew Sornborger “Variational Fast Forwarding for Quantum Simulation Beyond the Coherence Time.” Nature partner journal, in press https://arxiv.org/abs/1910.04292

Piotr Carnik, Andrew Arrasmith, Lukasz Cincio, and Patrick J. Coles, “Error mitigation with Clifford quantum-circuit data,” https://arxiv.org/abs/2005.10189

Technical contact: Lukasz Cincio

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