Engineering Nanodevices to Store Information the Quantum Way

Creating quantum computers which some people believe will be the next generation of computers, with the ability to outperform machines based on conventional technology—depends upon harnessing the principles of quantum mechanics, or the physics that governs the behavior of particles at the subatomic scale. Entanglement—a concept that Albert Einstein once called "spooky action at a distance"—is integral to quantum computing, as it allows two physically separated particles to store and exchange information.

Stevan Nadj-Perge, assistant professor of applied physics and materials science, is interested in creating a device that could harness the power of entangled particles within a usable technology. However, one barrier to the development of quantum computing is decoherence, or the tendency of outside noise to destroy the quantum properties of a quantum computing device and ruin its ability to store information.

Nadj-Perge, who is originally from Serbia, received his undergraduate degree from Belgrade University and his PhD from Delft University of Technology in the Netherlands. He received a Marie Curie Fellowship in 2011, and joined the Caltech Division of Engineering and Applied Science in January after completing postdoctoral appointments at Princeton and Delft.

He recently talked with us about how his experimental work aims to resolve the problem of decoherence.

What is the overall goal of your research?

A large part of my research is focused on finding ways to store and process quantum information. Typically, if you have a quantum system, it loses its coherent properties—and therefore, its ability to store quantum information—very quickly. Quantum information is very fragile and even the smallest amount of external noise messes up quantum states. This is true for all quantum systems. There are various schemes that tackle this problem and postpone decoherence, but the one that I'm most interested in involves Majorana fermions. These particles were proposed to exist in nature almost eighty years ago but interestingly were never found.

Relatively recently theorists figured out how to engineer these particles in the lab. It turns out that, under certain conditions, when you combine certain materials and apply high magnetic fields at very cold temperatures, electrons will form a state that looks exactly as you would expect from Majorana fermions. Furthermore, such engineered states allow you to store quantum information in a way that postpones decoherence. 

How exactly is quantum information stored using these Majorana fermions?

The fascinating property of these particles is that they always come in pairs. If you can store information in a pair of Majorana fermions it will be protected against all of the usual environmental noise that affects quantum states of individual objects. The information is protected because it is not stored in a single particle but in the pair itself. My lab is developing ways to engineer nanodevices which host Majorana fermions. Hopefully one day our devices will find applications in quantum computing.

Why did you want to come to Caltech to do this work?

The concept of engineered Majorana fermions and topological protection was, to a large degree, conceived here at Caltech by Alexei Kiteav [Ronald and Maxine Linde Professor of Theoretical Physics and Mathematics] who is in the physics department. A couple of physicists here at Caltech, Gil Refeal [professor of theoretical physics and executive officer of physics] and Jason Alicea [professor of theoretical physics], are doing theoretical work that is very relevant for my field.

Do you have any collaborations planned here?

Nothing formal, but I've been talking a lot with Gil and Jason. A student of mine also uses resources in the lab of Harry Atwater [Howard Hughes Professor of Applied Physics and Materials Science and director of the Joint Center for Artificial Photosynthesis], who has experience with materials that are potentially useful for our research.

How does that project relate to your lab's work?

There are two-dimensional, or 2-D, materials that are basically very thin sheets of atoms. Graphene—a single layer of carbon atoms—is one example, but you can create single layer sheets of atoms with many materials. Harry Atwater's group is working on solar cells made of a 2-D material. We are thinking of using the same materials and combining them with superconductors—materials that can conduct electricity without releasing heat, sound, or any other form of energy—in order to produce Majorana fermions.

How do you do that?

There are several proposed ways of using 2-D materials to create Majorana fermions. The majority of these materials have a strong spin-orbit coupling—an interaction of a particle's spin with its motion—which is one of the key ingredients for creating Majoranas. Also some of the 2-D materials can become superconductors at low temperatures. One of the ideas that we are seriously considering is using a 2-D material as a substrate on which we could build atomic chains that will host Majorana fermions.  

What got you interested in science when you were young?

I don't come from a family of scientists; my father is an engineer and my mother is an administrative worker. But my father first got me interested in science. As an engineer, he was always solving something and he brought home some of the problems he was working. I worked with him and picked it up at an early age.

How are you adjusting to life in California?

Well, I like being outdoors, and here we have the mountains and the beach and it's really amazing. The weather here is so much better than the other places I've lived. If you want to get the impression of what the weather in the Netherlands is like, you just replace the number of sunny days here with the number of rainy days there.

 

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Jessica Stoller-Conrad
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A Conversation with Stevan Nadj-Perge
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A conversation about using 2-D materials in the development of a device that could turn quantum computing concepts into usable technology.

Gilmartin Named Dean of Undergraduate Students

On July 1, 2016, Kevin Gilmartin, professor of English, will begin serving as Caltech's dean of undergraduate students.

In announcing Gilmartin's appointment, Joseph E. Shepherd, vice president for student affairs and the C. L. Kelly Johnson Professor of Aeronautics and Mechanical Engineering, described him as "an accomplished scholar and author who brings to this position twenty-five years of experience in teaching and mentoring our students, and who has shown a keen interest in the welfare of our undergraduate students in and outside of the classroom."

In his new role as dean of undergraduate students, Gilmartin will work on fostering academic and personal growth through counseling and support for student activities as well as acting as a liaison between students and faculty, says Shepherd.

A recipient the Feynman Prize, Caltech's highest teaching award, Gilmartin says he was attracted to the job of dean because "I have always found our students to be so interesting, and engaging. They are extraordinarily optimistic. They seem to have a positive attitude toward the world—they're curious, and they're open to new things. What more could you ask for?"

He says he sees his role as helping undergraduates develop and thrive. "I'm excited to work with students to help foster their intellectual and academic growth and their development as individuals," he says. "Our students are remarkably diverse and they have diverse interests. The Caltech curriculum is demanding, and focused, no doubt. But within it, and through it, our students do find so many opportunities."

He adds, "The dean's office provides essential support. But we can also encourage our students to do more than they are inclined to do, to challenge themselves, to try new things."

Gilmartin received his undergraduate degree in English from Oberlin College in 1985. He received both his MS ('86) and PhD ('91) in English from the University of Chicago, joining the faculty of Caltech in 1991.

Barbara Green, who has served as the interim dean over the past year will return to her regular position as associate dean in July. In his announcement, Shepherd thanked Green "for her work with our students and service to the Institute [and for] being so willing and committed to the success of our undergraduate student body."

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On July 1, 2016, Kevin Gilmartin, professor of English, will begin serving as Caltech's dean of undergraduate students.

Ditch Day? It’s Today, Frosh!

Today we celebrate Ditch Day, one of Caltech's oldest traditions. During this annual spring rite—the timing of which is kept secret until the last minute—seniors ditch their classes and vanish from campus. Before they go, however, they leave behind complex, carefully planned out puzzles and challenges—known as "stacks"—designed to occupy the underclassmen and prevent them from wreaking havoc on the seniors' unoccupied rooms.

Follow the action on Caltech's Facebook, Twitter, and Instagram pages as the undergraduates tackle the puzzles left for them to solve around campus. Join the conversation by sharing your favorite Ditch Day memories and using #CaltechDitchDay in your tweets and postings.

          

 

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DNA Origami: Folded DNA as a Building Material for Molecular Devices

Living things use DNA to store the genetic information that makes each plant, bacterium, and human being unique. The reproduction of this information is made possible because DNA's nucleotides—A's and T's, G's and C's—fit together perfectly, like matching jigsaw puzzle pieces. Engineers can take advantage of the matching between long strands of DNA nucleotides to use DNA as a kind of molecular origami, folding it into everything from nanoscale smiley face artwork to serious drug-delivery devices.

On Wednesday, May 25, at 8 p.m. in Beckman Auditorium, Paul Rothemund (BS '94), the inventor of the DNA origami technique, will explain how his group and groups around the world are using DNA origami in applications ranging from potential cancer treatments to devices for computing. Rothemund is research professor of bioengineering, computing and mathematical sciences, and computation and neural systems in the Division of Engineering and Applied Science at Caltech. Admission is free.

What do you do?

I use DNA and RNA as building materials to create shapes and patterns with a resolution of just a few nanometers. The smallest features in the DNA structures we make are about 20,000 times smaller than the pixels in the fanciest computer displays, which are each about 80 microns across. A large part of our work over the last 20 years has been just figuring out how to get DNA or RNA strands to fold themselves into a desired computer-designed shape. As we've mastered the ability to make whatever shape or pattern we desire, we've moved on to using these shapes as "pegboards" for arranging other nano-sized objects, such as protein enzymes, carbon-nanotube transistors, and fluorescent molecules.

Why is this important?

Every task in your body, from digesting food to moving your muscles to sensing light, is powered by tiny nanometer-scale biological machines, all built from the "bottom up" via the self-folding of molecules such as proteins and RNAs. The billions of transistors that make up the chips in our cell phones and computers are tens of nanometers in size, but they are built in a "top down" fashion using fancy printing processes in billion-dollar factories. Our goal is to learn how to build complex artificial devices the way biology builds natural ones—that is, starting from self-folding molecules that assemble together into larger more complex structures. In addition to vastly cheaper devices, this will enable completely new applications, such as man-made molecular machines that can make complex therapeutic decisions and apply drugs only where needed.

How did you get into this line of work?

As an undergraduate at Caltech, I had great difficulty trying to decide how to combine my diverse interests in computer science, chemistry, and biology. Fortunately, the late Jan L. A. van de Snepscheut introduced his computer science class to the hypothetical idea of building a DNA Turing machine—a very simple machine which can nevertheless run every possible computer program. He challenged us, suggesting that someone who knew about both biochemistry and computer science could come up with a concrete way to build such a DNA computer. For a project class in information theory with Yaser Abu-Mostafa, a professor of electrical engineering and computer science, I came up with a pretty inefficient, yet possible, way to do this. At the time, I couldn't interest any Caltech professors in building my DNA computer, but shortly after, USC professor Len Adleman published a paper on a more practical DNA computer in Science. I joined Adleman's lab at USC as a graduate student, and I've been trying to use DNA to build computers or other complex devices ever since. I returned to Caltech as a postdoc in 2001 and became a research professor in 2008.

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A preview of Paul Rothemund's upcoming Watson Lecture.

Seven from Caltech Elected to National Academy of Sciences

Three Caltech professors and four Caltech alumni have been elected to the prestigious National Academy of Sciences (NAS). The announcement was made Tuesday, May 3.

Raymond Deshaies is a professor of biology, investigator at the Howard Hughes Medical Institute, and executive officer for molecular biology. Deshaies's work focuses on understanding the basic biology of protein homeostasis, the mechanisms that maintain a normal array of functional proteins within cells and organisms. He is the founder of Caltech's Proteome Exploration Laboratory to study and sequence proteomes, which are all of the proteins encoded by a genome.

John Eiler is the Robert P. Sharp Professor of Geology and professor of geochemistry, as well as the director of the Caltech Microanalysis Center. Eiler uses geochemistry to study the origin and evolution of meteorites and the earth's rocks, atmosphere, and interior. Recently, his team published a paper detailing how dinosaurs' body temperatures can be deduced from isotopic measurements of their eggshells.

Ares Rosakis is the Theodore von Kármán Professor of Aeronautics and Mechanical Engineering in the Division of Engineering and Applied Science. His research interests span a wide spectrum of length and time scales and range from the mechanics of earthquake seismology, to the physical processes involved in the catastrophic failure of aerospace materials, to the reliability of micro-electronic and opto-electronic structures and devices.

Deshaies, Eiler, and Rosakis join 70 current Caltech faculty and three trustees as members of the NAS. Also included in this year's new members are four alumni: Ian Agol (BS '92), Melanie S. Sanford (PhD '01), Frederick J. Sigworth (BS '74), and Arthur B. McDonald (PhD '70).

The National Academy of Sciences is a private, nonprofit organization of scientists and engineers dedicated to the furtherance of science and its use for the general welfare. It was established in 1863 by a congressional act of incorporation signed by Abraham Lincoln that calls on the academy to act as an official adviser to the federal government, upon request, in any matter of science or technology.

A full list of new members is available on the academy website at: http://www.nasonline.org/news-and-multimedia/news/may-3-2016-NAS-Electio...

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Three faculty members and four alumni have been elected to the National Academy of Sciences.
Wednesday, May 11, 2016
Noyes 147 (J. Holmes Sturdivant Lecture Hall) – Arthur Amos Noyes Laboratory of Chemical Physics

Administrative Contact Information Session

Smart Charging Network for EVs Installed at Caltech

In an effort to reduce carbon dioxide emissions in our environment and begin a campuswide shift to the use of renewable resources, a research group led by Steven Low, professor of computer science and electrical engineering in the engineering and applied science division, has installed 54 electric vehicle (EV) charging stations for use by all Caltech and JPL personnel and visitors. The stations, four of which are handicapped-accessible, were first installed in the California Parking Structure in February and are currently free to use.

Depending on a car's charger, the stations will fully charge an EV in about five hours. Users can monitor the stations—whether they are occupied or available, as well as whether the occupied stations are currently charging or done charging—via the Caltech Adaptive Charging Network (ACN) site at http://ev.caltech.edu/.

"Electrification of our transportation system will be important because today vehicles consume more than a quarter of our energy and emit more than a quarter of our energy-related carbon dioxide [CO2]," says Low, who was awarded a Caltech Innovation Initiative (CI2) grant last year to fund the design, building, and installation of the EV charging system, as well as its power-distribution infrastructure. "Electrification will not only greatly reduce CO2 emission, but EVs can also be critical resources to help integrate renewable sources, such as wind and solar power, into our electric grid. One of the key enablers to mass EV adoption is the availability of smart charging networks."

Because there are now so many stations on campus and charging EVs can require a substantial amount of electricity (most EVs charge at 7 kilowatts, the equivalent of simultaneously running 70 desktop computers), Low developed Caltech's adaptive charging network, which uses a smart algorithm to coordinate the charging schedule with the Institute's existing electrical infrastructure. This program helps minimize energy usage; as of now, the stations are consuming about 200 kilowatt-hours per day, only a fraction (0.00006 percent) of Caltech's total electrical usage. And, according to John Onderdonk, director of sustainability programs at Caltech, about 30 percent of the electricity at each charging station is from carbon-free renewable sources.

The ACN project is helping the Institute prepare for the vehicle of the future, Onderdonk notes. "Caltech's Facilities Management department is also benefiting from the project by learning about EV use patterns so that we can identify the opportunities and challenges that may come with integrating large numbers of EVs into the campus electrical infrastructure," he says.

Implementation of publicly available EV charging programs like Caltech's pilot ACN also can be beneficial for limiting energy usage in the long term. "Compared with charging these EVs at homes individually, ACN requires a smaller total power distribution capacity and can better use renewable electricity," says Low.

"We believe having ample charging stations available is the key to widespread EV adoption," says George Lee (MS '10), who is volunteering in Low's lab to continue contributing to this project. "Most installations outside Caltech only have a few EV charging stations, due to the high cost of upgrading electrical infrastructure and construction. Our technique allows a large number of stations to be installed at a reasonable cost."

Low's CI2 funding will allow the charging stations to be free to use until the end of the academic year. After that—and depending on renewal of the CI2 grant for phase 2 of the project, which would be focused on further developing the software based on data collected from the newly installed chargers—there will be a potential cost of less than $0.20 per kilowatt-hour. (Private residences purchasing energy from Pasadena Water and Power spend between $0.13 and $0.38 per kilowatt-hour delivered, depending on the specific plan and time of day.) While charging at home at night is the cheapest option, says Lee, charging during the day is cheaper at Caltech, where the rate is the same at all times, than at a private residence. "This financial structure helps maximize EV adoption because it allows for people who cannot install chargers at home to own an EV at reasonable electricity costs," Lee says.

When the research project concludes in April 2017, the chargers will become the property of Caltech's facilities department, at which point their fee structure will need to be reassessed. In addition to the current installation, Low foresees the need for additional charging stations in the future as EV use increases.

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A research group led by professor Steven Low has installed 54 electric vehicle (EV) charging stations for use by all Caltech and JPL personnel and visitors.

Resnick Sustainability Institute Boosts Caltech's Earth Day Celebration

The Resnick Sustainability Institute—Caltech's hub for projects aimed at tackling some of the toughest sustainability-focused problems our society faces—played a key role in Caltech's Earth Week celebration, during which various events were held to show support for environmental protection and achieving a sustainable future.

For example, on April 19, Resnick fellow Bryan Hunter gave a talk on "The 21st Century Solar Army," which focused on his volunteer work with Caltech's NSF Center for Chemical Innovation in Solar Fuels. Among CCI Solar's volunteers are Resnick postdoctoral scholars Bradley Brennan and Sonja Francis, whose efforts have included working with school teachers to show them how to build and test simple and cheap solar cells; the teachers then take these activities back to their classrooms.

The Resnick Sustainability Institute's 17 graduate student fellows and 10 postdoctoral scholars are actively engaged in research involving everything from solar fuels and photovoltaics to improved catalysts for greener industrial processes, carbon capture and storage, greenhouse gas assessment, wastewater treatment, and more.

Recently, postdoctoral scholar Christopher Prier and his colleagues in Frances Arnold's laboratory described a method for the synthesis of valuable amines using engineered variants of cytochrome P450, a common iron-containing enzyme, in the journal Angewandte Chemie. Because enzymatic processes are typically environmentally benign, Prier notes, his work contributes to the greening of chemical synthesis.

Francis and colleagues described in the journal ACS Catalysis a new catalyst made of two metals, nickel and gallium, which can be used for converting carbon dioxide and water into hydrocarbons like methane, ethane, and ethylene. Currently, no electro-catalyst exists that can convert carbon dioxide with both high efficiency and selectivity to hydrocarbons or even alcohols, Francis notes.

Additionally, in an upcoming issue, the Journal of the American Chemical Society will spotlight an improved catalyst for sustainable fertilizer production developed by Resnick fellow Niklas Thompson and others from Resnick Institute director Jonas Peters' research group. This same research also won the 2016 Dow Sustainability Innovation Student Challenge Award at Caltech.

Learn more about the Resnick Sustainability Institute at Caltech at http://resnick.caltech.edu.

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The Resnick Sustainability Institute played a key role in Caltech's Earth Week celebration.

American Academy of Arts and Sciences Elects Two from Caltech

The American Academy of Arts and Sciences has elected two Caltech professors—Hirosi Ooguri and Rob Phillips—as fellows. The American Academy is one of the nation's oldest honorary societies; this class of members is its 236th, and it includes a total of 213 scholars and leaders representing such diverse fields as academia, business, public affairs, the humanities, and the arts.

Hirosi Ooguri is the director of the Walter Burke Institute for Theoretical Physics and the Fred Kavli Professor of Theoretical Physics and Mathematics in the Division of Physics, Mathematics and Astronomy. He works on quantum field theory and superstring theory, aiming to invent new theoretical tools to solve fundamental questions in physics.

Rob Phillips is the Fred and Nancy Morris Professor of Biophysics and Biology and has appointments in the Division of Engineering and Applied Science and the Division of Biology and Biological Engineering. He focuses on the physical biology of the cell using biophysical theory as well as single-molecule and single-cell experiments.

Ooguri and Phillips join 86 current Caltech faculty as members of the American Academy. Also included in this year's list are two Caltech trustees, David Lee (PhD '74) and Ron Linde (MS '62, PhD '64); as well as three additional alumni: Gerard Fuller (MS '77, PhD '80), Melanie Sanford (PhD '01), and Robert Schoelkopf (PhD '95).

Founded in 1780 by John Adams, James Bowdoin, John Hancock, and other scholar-patriots, the academy aims to serve the nation by cultivating "every art and science which may tend to advance the interest, honor, dignity, and happiness of a free, independent, and virtuous people." The academy has elected as fellows and foreign honorary members "leading thinkers and doers" from each generation, including George Washington and Ben Franklin in the 18th century, Daniel Webster and Ralph Waldo Emerson in the 19th, and Albert Einstein and Woodrow Wilson in the 20th. This year's class of fellows includes novelist Colm Tóibín, La Opinión publisher and CEO Monica Lozano, jazz saxophonist Wayne Shorter, former Botswanan president Festus Mogae, and autism author and spokesperson Temple Grandin.

A full list of new members is available on the academy website at www.amacad.org/members.

The new class will be inducted at a ceremony on October 8, 2016, in Cambridge, Massachusetts.

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Hirosi Ooguri and Rob Phillips have been elected as members of the American Academy of Arts and Sciences.

Aliso Canyon, Methane, and Global Climate: A Conversation with Paul Wennberg

On October 23, 2015, the Aliso Canyon underground storage facility for natural gas in the San Fernando Valley—the fourth largest of its kind in the United States—had one of its wells blow out, leading to a large release of methane. The leak was not fully under control until February 11, 2016. In the interim, residents of nearby neighborhoods were sickened by the odorants added to the gas, thousands of households were displaced, and California's governor declared a state of emergency for the area. The story made international headlines; the BBC's headline, for example, read, "California methane leak 'largest in US history.'"

The leak was indeed large and undoubtedly difficult for the residents of the area. However, Caltech's Paul Wennberg says there is also a bigger picture to keep in mind: enormous methane and carbon dioxide (CO2) emissions occur all the time, with troubling implications for global climate. Wennberg is Caltech's R. Stanton Avery Professor of Atmospheric Chemistry and Environmental Science and Engineering, executive officer for Environmental Science and Engineering, and director of the Ronald and Maxine Linde Center for Global Environmental Science.

We recently sat down with him to talk about methane emissions and how to put the Aliso Canyon event into perspective.

What was your involvement with the Aliso Canyon event?

We have a greenhouse gas remote sensing system here at Caltech that is part of TCCON—the Total Carbon Column Observing Network. The day after the Aliso Canyon leak started, we observed something really weird in the air above Pasadena. There was a large, big plume of methane and ethane gas that came over. We now know that it was from the Aliso Canyon facility. We are providing data for the final analyses of the leak.

In the past you have suggested that the methane emissions from Los Angeles are much larger than was previously included in models.

Right. Thankfully, models are now catching up as we learn more from the data.

What does the Aliso Canyon event suggest about Los Angeles's methane emissions in general?

Aliso Canyon was a very dramatic event. Everyone heard about it worldwide. The leak continued for about 100 days, and yet it only doubled the amount of methane being emitted by LA during that period. This was a tragedy for the people living next to it, who had to deal with horrible nausea and other side effects of the chemicals associated with the natural gas. But from a climate point of view, the methane leak was actually quite trivial.

There are enormous amounts of methane being released into the atmosphere globally as a result of human activity. That is certainly true of LA, but as far as climate goes, it doesn't matter whether it's released in LA or New Zealand. On the timescale that methane sticks around in the atmosphere, it gets well mixed and affects the entire planet.

How much methane is emitted per year?

About three hundred teragrams [Tg; one teragram is equivalent to one billion kilograms] of methane are emitted every year by people and the activities of people, like agriculture and energy. Los Angeles emits about 0.4 Tg. That means that of the human methane emissions, LA as a total is one part in a thousand—not nothing, but a pretty small amount.

For perspective, Aliso Canyon emitted around 0.1 Tg. It was a big event, but what it really illustrates is how big a challenge we truly face. There are many sources emitting methane into the atmosphere and they are very diffuse. Reducing them will require hard work on many, many fronts. So it's not just, "If we solve this one problem, everything will be beautiful in the world."

You could imagine the response to the Aliso Canyon leak might be that we would all of a sudden focus all of our efforts trying to prevent leaks in natural gas storage facilities. That would not be the right answer from a climate perspective.

How should people go about eliminating methane emissions?

There is not "one" fix. Each source requires a different strategy for mitigation.

First, there is fixing leaks in the pipelines and storage facilities.

Then, it turns out that ruminants like cows and sheep produce a lot of methane—probably a third, if not more, of the human emissions. A paper about this, recently in Science, suggests that an important part of the recent increases in methane is coming from agriculture. Depending on what you feed these ruminants, they produce less methane. They eat grass, but they can't metabolize it: they have a fermenter going in their bellies—a whole microbiome that breaks the grass down into smaller things like acetate that they can metabolize. Depending on the microbiome of their guts, the cows and sheep make more or less methane. And it turns out that you can manage this.

Then there are the wetlands used for rice agriculture. Methane is produced anaerobically—in places with no oxygen—by Archaea. If you have a flooded rice paddy, the methane is produced at the roots and is transpired through the rice plants into the atmosphere. Quite a few studies now show that if you can change your rice agricultural practices to allow the fields to dry periodically, the methane emissions drop hugely.

If you were able to fix all of these things what would the impact be in terms of climate change?

If we could really knock the methane emissions back to what they were before people started emitting methane, it would be a large change. It would be a half a watt per meter squared. The total global warming would drop by around 25 percent.

How does the importance of reducing methane emissions compare to the importance of reducing carbon dioxide emissions?

Globally, methane is important. It's maybe a third of the climate forcing of CO2—that is, the increase in methane has contributed about one third of the total change in Earth's climate over the last 100 years. In terms of climate impact, however, the methane emissions from people in Los Angeles are absolutely dwarfed by their CO2 emissions—all of our driving, going on airplanes, and everything else that we do. Still, if we are to reduce our global warming potential and the amount of greenhouse gasses we emit to the atmosphere, methane has to be part of the equation.

We like to think that we can solve these problems by fixing singular events, but climate doesn't work that way. We're talking about the emissions of 7 billion people. If it were that this was produced by 100 events like Aliso Canyon, this would be a simple problem: we solve the 100 problems, and we're done. But it's all of us, and it's all of what we eat, it's all of the energy that we use, it's all of the miles that we drive. It's a much more complex problem.

What work is your group currently doing in terms of methane?

One of the things we've been doing is long-term monitoring. Natural gas is mostly methane (CH4) but there's also ethane (C2H6) in it and this provides a way of separating the signature of methane emitted from agriculture, which has no ethane, and emissions from natural gas, which does.

Over the last five years or so, the production of oil in the United States has increased hugely, and associated with that oil production is natural gas, and therefore methane and ethane. Traditionally, most of the ethane produced at a wellhead was pulled off and sent to the plastic industry. With the changing oil production, the market has become flooded in ethane: there's simply not enough plastic to be made. When the industry can't sell the ethane to the plastic industry, they simply leave it in the natural gas. We see this in the natural gas delivered to Los Angeles. Five years ago natural gas had about 2 percent ethane. Now it's 5 percent—it's more than doubled. What we've seen—and this has nothing to do with Aliso Canyon—is that over the last five years, the amount of ethane in the air over Pasadena has increased.

That's important because it tells us that a significant fraction of the methane that's being released in LA is coming from natural gas brought into Los Angeles. This has been a topic of a lot of debate. Is the big methane emitter the oil production down in the Long Beach area? Is it waste treatment plants? Is it garbage dumps? What we find is that about half of all the methane emitted in this part of LA is gas that originally came in on a pipeline.

How do you know that?

We actually know from the gas company how much ethane is in the natural gas. They report this publically from one of their storage fields and this matches the ethane in samples of the natural gas coming into our buildings.

Are there other projects under way at Caltech to study methane emissions?

Christian Frankenberg [associate professor of environmental science and engineering at Caltech and a JPL research scientist] has been leading an effort to build remote sensing instruments that allow imaging of methane plumes. Using small spectrometers on airplanes, he has flown over areas where you might have a lot of methane emissions and identified individual sources. Last year they were able to find individual pipelines that were leaking in Colorado and in New Mexico. They found several big leaks from pipelines and were able to tell the pipeline operators, who shut them down and fixed them.

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We recently sat down with Paul Wennberg to talk about methane emissions and how to put the Aliso Canyon event into perspective.

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