Contemplating a Quantum Future

Last week, Caltech's Institute for Quantum Information and Matter (IQIM) honored the legacy and contributions of theoretical physicist Richard Feynman, marking 50 years since he received the Nobel Prize in Physics for his work on quantum electrodynamics. Feynman spent much of his career working to understand better the laws and implications of quantum mechanics—the rules that dictate the bizarre behavior of matter at the scale of individual atoms and particles. He foresaw how quantum mechanics could lead to the development of nanotechnology and even a quantum computer that could solve problems that would be intractable for conventional computers. Over two days, IQIM hosted two events to celebrate that vision by exploring the research and development currently underway at what might be called the quantum frontier.

The first event, "One Entangled Evening," aimed to delight, educate, and inspire an audience not only of scientists and engineers but also of artists, entertainers, and members of the public. Among the highlights of the evening were a video tribute to Feynman by Microsoft cofounder Bill Gates; a song and dance about quantum mechanics performed by artist Gia Mora and John Preskill, the Richard P. Feynman Professor of Theoretical Physics at Caltech and director of IQIM; and a screening of a short video titled Anyone Can Quantum, narrated by actor Keanu Reeves and featuring actor Paul Rudd playing a game of "quantum chess" with renowned physicist Stephen Hawking.

The following day, IQIM hosted an all-day Quantum Summit that brought together scientists and engineers from academia and industry to discuss progress in the quantum realm.

One session featured a panel discussion about the future of quantum computers with researchers from Google, HP Laboratories, IBM, Intel, the Institute for Quantum Computing, and Microsoft. Moderated by Jennifer Ouellette, senior science editor at Gizmodo.com, the discussion started with brief descriptions of the approach that each company or institute is taking in the quest for a quantum computer as well as answers to the questions, "Why quantum computing, and why now?"

Ray Beausoleil leads the Large-Scale Integrated Photonics research group at HP Laboratories. His team is currently trying to put thousands of nonlinear optical devices on a chip and to get them interacting coherently—in a way that their quantum properties are not disturbed by outside noise. As for his answer to the "Why quantum now?" question, "If you're a big computer company, you're looking at quantum computing because you know that, depending on your point of view … Moore's Law is in danger of being over," he explained. "So we have to start thinking more energetically about what computing will look like in 10 to 20 years."

"People have been saying that Moore's Law was over since about the time Richard Feynman proposed the quantum computer," countered Jim Clarke, manager of quantum hardware and novel memory research at Intel. Intel was cofounded by Gordon Moore (PhD '54), the originator of Moore's Law—the 1965 prediction that the amount of processing power, based on the number of transistors in a circuit, will double about every two years. "My take is Moore's Law is not ending," Clarke continued. "In fact, I think we need at least a couple more generations of Moore's Law just to be able to enable a large-scale quantum computer."

IBM Fellow Charles Bennett said that IBM is working to get a small number of superconducting qubits to work coherently and to understand what those qubits are doing. "That is a tremendous task, and we're putting a lot of effort into that," he said.

Parsa Bonderson, a theoretical physicist from Microsoft's Station Q at UC Santa Barbara, said that while Microsoft is keeping its eyes on a number of approaches, its main focus is on topological quantum computing, an idea devised in the 1990s by Alexei Kitaev, now the Ronald and Maxine Linde Professor of Theoretical Physics and Mathematics at Caltech. The approach attempts to develop much more stable qubits, known as topological qubits, that would be less sensitive to the disturbances that destroy the quantum properties of all other qubits. (Jason Alicea, professor of theoretical physics at Caltech, provided an overview of topological quantum computing in an earlier session at the summit.)

And why now? Bonderson answered, "We're starting to really feel like this could be within reach this time."

Google, for one, seems to agree. The company made headlines in 2013 when it bought a system from D-Wave Systems, a startup company that has built an early prototype of a limited quantum computer. Google's main goal, noted its director of engineering Hartmut Neven, is "to get a practical quantum computer as quickly as we can."

What can be done with a quantum computer? Krysta Svore, a senior researcher in Microsoft's Quantum Architectures and Computation Group, works to address that question and presented a number of potential answers in a morning session at the summit. Some of the ideas that reach beyond improving scientists' ability to study quantum systems include improving machine learning and simulating chemicals and chemical reactions more precisely in order to facilitate drug design and improving machine learning.

Ouellette asked the panelists what they thought might be possible with a small quantum computer, perhaps with 100 qubits.

Ray Laflamme, executive director of the Institute for Quantum Computing at the University of Waterloo, in Ontario, said he would use such a computer to help train students, postdocs, and young faculty "to think quantumly."

Intel's Clarke spoke about modeling the dynamics of molecules, including ozone and carbon dioxide, which are just out of reach of conventional computers. "Well, that's climate change, so that resonates with a lot of people," he said. "If you go even further, you get into the protein space. … Misfolded proteins are the genesis of so many diseases—cancer, multiple sclerosis, and others."

Microsoft's Bonderson suggested that a small quantum computer might be useful for designing a better quantum computer. And Bennett reminded everyone that the quantum computer would likely do more than simply provide more processing power. "It's not going to be the solution to the supposed problem of the demise of Moore's Law. It's going to change things in a way that is more interesting," he said. "It's like saying if we've got radio, how much better does that make things than if we just had the telegraph or we just had post offices?"

Beausoleil added that he would not let himself try to determine how the quantum computer should be used. Instead, he said, "I'd put it online as rapidly as possible and let people who are not physicists start experimenting."

And Google's Neven talked about the potential applications of a full-fledged quantum computer in the artificial intelligence (AI) field. Noting that formulating fundamental laws of physics is extremely difficult and something that only a tiny fraction of people can do, he said, "The question is: Is this really a task that, as physics develops further, remains a human task? Or is this, rather, a task that we should hand over to machines?"

He said that he believed that forms of artificial intelligence could prove to be better physicists and that quantum computing would be involved. "I would dare to conjecture that the most creative systems we will ever see will be quantum AI systems," he said.

During other sessions at the summit, John Martinis of Google spoke about quantum simulation with superconducting qubits; Oskar Painter, the John G. Braun Professor of Applied Physics at Caltech, presented on acoustic quantum transducers; and David Wineland, a Nobel laureate from National Institute of Standards and Technology, described the latest thinking on entangled trapped ions.

IQIM, which spans Caltech's Divisions of Physics, Mathematics and Astronomy and Engineering and Applied Science, is a Physics Frontiers Center supported by the National Science Foundation and by the Gordon and Betty Moore Foundation. 

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Contemplating a Quantum Future
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IQIM hosted a Quantum Summit that brought scientists and engineers together to discuss progress in the quantum realm.

Bock Receives Award for Astronomical Instrumentation

Jamie Bock, professor of physics and Jet Propulsion Laboratory senior research scientist, has received the Joseph Weber Award for Astronomical Instrumentation from the American Astronomical Society (AAS). The award citation notes his "development of low-noise 'spider-web' bolometers"—devices for measuring radiation—that have enabled fundamental measurements of the cosmic microwave background. The award is given annually for the design, invention, or significant improvement of instrumentation leading to advances in astronomy.

The spider-web bolometers, developed to detect millimeter-wave and far-infrared radiation, enabled a generation of ground-based and balloon-borne experiments for mapping variations in the cosmic microwave background, or CMB, which is thermal radiation from the early universe. The most notable of the telescopes employing these bolometers,, the BOOMERanG balloon experiment, made measurements of the CMB that ultimately determined that the overall geometry of the universe is very nearly flat. Detector arrays later flew on the Planck spacecraft and provided what is currently the ultimate measurement of the CMB over the full sky, and flew as well on the Herschel Space Observatory, a 3.5-meter space-based telescope for far-infrared astronomy. Modern descendants of the spider-web bolometers are actively engaged in measuring CMB polarization from Earth's South Pole.

After receiving his PhD in physics from UC Berkeley in 1994, Bock joined JPL as a research scientist and Caltech as a visiting associate. He was named a senior research scientist and full professor in 2012.

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Jamie Bock has received the Joseph Weber Award for Astronomical Instrumentation.

JPL News: Uranus as seen by NASA's Voyager 2

Humanity has visited Uranus only once, and that was 30 years ago. NASA's Voyager 2 spacecraft got its closest look at the mysterious, distant, gaseous planet on January 24, 1986.

Voyager 2 sent back stunning images of the planet and its moons during the flyby, which allowed for about 5.5 hours of close study. The spacecraft got within 50,600 miles (81,500 kilometers) of Uranus during that time.

"We knew Uranus would be different because it's tipped on its side, and we expected surprises," said Voyager mission project scientist Ed Stone, who is also Caltech's David Morrisroe Professor of Physics and vice provost for special projects. Stone has served as project scientist since 1972, continuing in that role today.

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Hopkins Receives Honors from American Astronomical Society

Assistant Professor of Theoretical Astrophysics Philip Hopkins has received the Helen B. Warner Prize for Astronomy from the American Astronomical Society (AAS) for his research in galaxy formation and evolution, and the growth of massive black holes. The award is given annually for significant contributions to observational or theoretical astronomy during the five years preceding the award.

"It is an incredible honor to be awarded the Warner prize," Hopkins says. "The previous winners are a prestigious company, including many of my own idols and mentors in astrophysics, and it is amazing to be listed among these giants in our field."

Hopkins studies the formation of astronomical objects like galaxies, stars, and supermassive black holes. Leading the Feedback in Realistic Environments (FIRE) project, he and his group aim to synthesize theoretical models and observations, and bring together experts on these different phenomena to understand how they interact.

"After stars form, they aren't just 'done,'" Hopkins says. "They do important things like exploding as supernovae—and the energy released in these explosions can throw around interstellar matter and actually launch winds out of galaxies that carry away most of the matter which would otherwise have formed more stars."

Hopkins and his group have shown that these so-called feedback loops between stars, black holes, and galaxies are crucial to understanding the masses and structures of galaxies. The AAS award citation describes Hopkins as a "world expert in stellar feedback" and his work as giving "great insight into the role of galaxy mergers on galaxy properties as well as quasar activation."

"At a profound level, we have realized that seemingly diverse populations in our universe—quasars, starbursts, ultraluminous galaxies, 'red and dead' galaxies, galaxy mergers, star clusters, planets, and more—are all tightly connected to one another in a constantly interacting ecosystem," he says.

Previous recipients of the award include Professor of Theoretical Astrophysics and Executive Officer for Astronomy Sterl Phinney (BS '80), and Shri Kulkarni, the John D. and Catherine T. MacArthur Professor of Astronomy and Planetary Science.

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An Entangled Evening of Quantum Science

Caltech will celebrate the past and present of quantum science and consider future possibilities that might include enhancing medical diagnosis and treatment, expanding and refining communication, and building an even greater understanding of our universe. 

For nearly a century, Caltech has been a leader in advancing and shaping our understanding and application of fundamental physics and quantum science.

This leadership is exemplified by the 15 Nobel Prizes that have gone to the Institute's faculty and alumni in the field. These range from the 1923 Nobel Prize given to the Institute's first president, Robert A. Millikan, for his pioneering work elucidating the properties of electrons and photons to, most recently, the achievements of alumnus Arthur McDonald (PhD '70), whose measurements of the properties of neutrinos earned him the 2015 Nobel Prize. 

"We're determined that Caltech will stay at the forefront of physics in the future as it has in the past," says John Preskill, the Richard P. Feynman Professor of Theoretical Physics and director of the Institute for Quantum Information and Matter (IQIM). "This means we'll continue to explore matter at the smallest possible distance scales and the universe at the largest scales. These topics are just as exciting now as they've ever been." 

And indeed, today, Caltech continues to lead the development of quantum science and technology in areas ranging from quantum information to computation, condensed matter, and metrology. Much of this research, which is often conducted across disciplines, has the potential to lead to scientific breakthroughs and technological advances.

On Tuesday, January 26, and Wednesday, January 27, Caltech will celebrate the past and present of quantum science and consider future possibilities that might include enhancing medical diagnosis and treatment, expanding and refining communication, and building an even greater understanding of our universe. 

The two-day event—beginning with a public program titled "One Entangled Evening" and followed by a daylong Quantum Summit—focuses on the legacy and vision of Nobel Laureate Richard Feynman, who essentially launched the field of nanotechnology and quantum science with his 1959 lecture, "There's Plenty of Room at the Bottom."

The Quantum Summit will bring together technology leaders and scientists from several multinational companies and other organizations to consider what the summit's organizers call "our mind-bending quantum future" and the implications of this research for society.

"What sparked the idea for a celebratory event was the realization that Richard Feynman received the Nobel Prize in Physics 50 years ago last month," says Preskill, whose IQIM is one of the organizers of "One Entangled Evening." "Aside from being a great scientist, Feynman was legendary for his success at conveying the excitement of science to broad audiences. We'll be doing appropriate homage to Feynman if 'One Entangled Evening' turns out to be entertaining as well as inspiring for the audience." 

"One Entangled Evening" will feature appearances by Feynman's daughter, Michelle Feynman; Caltech president Thomas F. Rosenbaum; Nobel Laureate David Wineland; Krysta Svore, manager of the Quantum Architectures and Computation Group at Microsoft Research; Preskill; and Internet entrepreneur and philanthropist Yuri Milner. 

Bill Gates is scheduled to provide a taped tribute to Feynman, while Stephen Hawking and actor Paul Rudd will compete onscreen in a brief quantum chess match, a version of the classic game of strategy that follows the rules of probability and uncertainty and treats each piece as a quantum particle. (IQIM scientists consulted on Rudd's 2015 film, Ant-Man—which explores the quantum realm—and were instrumental in developing the script.) Quantum chess was created by USC graduate student Chris Cantwell, whose PhD adviser, Todd Brun, is a Caltech alumnus (PhD '94) and visiting professor. 

For more about the event, visit the event webpage.

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JPL News: NuSTAR Finds Cosmic Clumpy Doughnut Around Black Hole

The most massive black holes in the universe are often encircled by thick, doughnut-shaped disks of gas and dust. This deep-space doughnut material ultimately feeds and nourishes the growing black holes tucked inside.

Until recently, telescopes weren't able to penetrate some of these doughnuts, also known as tori.

"Originally, we thought that some black holes were hidden behind walls or screens of material that could not be seen through," said Andrea Marinucci of the Roma Tre University in Italy, lead author of a new Monthly Notices of the Royal Astronomical Society study describing results from NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, and the European Space Agency's XMM-Newton space observatory.

"NuSTAR was built to peer deep into the hearts of dust-enshrouded galaxies. By extending its reach to high energy X-rays, which are inherently penetrating, NuSTAR can study objects like this which would otherwise be invisible to low energy X-ray telescopes," says Fiona Harrison, NuSTAR's principal investigator, as well as Caltech's Benjamin M. Rosen Professor of Physics and Astronomy and the Kent and Joyce Kresa Leadership Chair of the Division of Physics, Mathematics and Astronomy.

With its X-ray vision, NuSTAR recently peered inside one of the densest of these doughnuts known to surround a supermassive black hole. This black hole lies at the center of a well-studied spiral galaxy called NGC 1068, located 47 million light-years away in the Cetus constellation.

The observations revealed a clumpy, cosmic doughnut.

"The rotating material is not a simple, rounded doughnut as originally thought, but clumpy," said Marinucci.

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15 for 2015: The Year in Research News at Caltech

The year 2015 proved to be another groundbreaking year for research at Caltech. From seeing quantum motion, to reconfiguring jellyfish limbs, to measuring stellar magnetic fields, researchers continued to ask and answer the deepest scientific questions.

In case you missed any of them, here are 15 stories highlighting a few of the discoveries, methods, and technologies that came to life at Caltech in 2015.

 

 

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Here are 15 stories highlighting a few of the discoveries, methods, and technologies that came to life at Caltech in 2015.

15 for 2015: The Year in Research News at Caltech

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Credit: K.Batygin/Caltech

New Research Suggests Solar System May Have Once Harbored Super-Earths

Thanks to recent surveys of exoplanets—planets in solar systems other than our own—we know that most planetary systems typically have one or more super-Earths (planets that are substantially more massive than Earth but less massive than Neptune) orbiting closer to their suns than Mercury does. In March, researchers showed that our own solar system may have once had these super-Earths, but they were destroyed by Jupiter's inward and outward migration through the solar system. This migration would have gravitationally flung small planetesimals through the solar system, setting off chains of collisions that would push any interior planets into the sun.
Credit: Lance Hayashida/Caltech and the Hoelz Laboratory/Caltech

Caltech Biochemists Shed Light on Cellular Mystery

The nuclear pore complex (NPC) is an intricate portal linking the cytoplasm of a cell to its nucleus. It is made up of many copies of about 34 different proteins. Around 2,000 NPCs are embedded in the nuclear envelope of a single human cell and each NPC shuttles hundreds of macromolecules of different shapes and sizes between the cytoplasm and nucleus. In February, Caltech biochemists determined the structure of a significant portion of the NPC called the outer rings; in August, the same group solved the structure of the pore's inner ring. Understanding the structure of the NPC could lead to new classes of cancer drugs as well as antiviral medicines.
Credit: iStockphoto

Research Suggests Brain's Melatonin May Trigger Sleep

For decades, supplemental melatonin has been sold over the counter as a sleep aid despite the absence of scientific evidence proving its effectiveness. Few studies have investigated melatonin produced naturally in the human body. This March, Caltech researchers studying zebrafish—animals that, like humans, are awake during the day and asleep at night—determined that the melatonin hormone does help the body fall asleep and stay asleep. Specifically, they found that zebrafish larvae that could not produce melatonin slept for only half as long as normal larvae.
Credit: Gregg Hallinan/Caltech

Advances in Radio Astronomy

In May, a new radio telescope array called the Owens Valley Long Wavelength Array (OV-LWA) saw its first light. Developed by a consortium led by Caltech, the OV-LWA has the ability to image simultaneously the entire sky at radio wavelengths with unmatched speed, helping astronomers to search for objects and phenomena that pulse, flicker, flare, or explode.

In July, Caltech researchers used both radio and optical telescopes to observe a brown dwarf located 20 light-years away and found that these so-called failed stars host powerful auroras near their magnetic poles.
Credit: Michael Abrams and Ty Basinger

Injured Jellyfish Seek to Regain Symmetry

Some kinds of animals can regrow lost limbs and body parts, but moon jellyfish have a different strategy. In June, Caltech researchers reported that the star-shaped eight-armed moon jellyfish rearranges itself when injured to maintain symmetry. It is hypothesized that the rearrangement helps to preserve the jellyfish's propulsion mechanism.
Credit: NASA/JPL-Caltech

Geologists Characterize Nepal Earthquake

In April, a magnitude 7.8 earthquake rocked Nepal. While the damage was extensive, it was not as severe as many geologists predicted. This year, a Caltech team of geologists used satellite radar imaging data and measurements from seismic instruments in Nepal to create models of fault rupture and ground movement. They found that the quake ruptured only a small fraction of the "locked" tectonic plate and that there is still the potential for the locked portion to produce a large earthquake.
Credit: Caltech/JPL

New Polymer Creates Safer Fuels

Plane crashes cause devastating damage, but this damage is often exacerbated by the highly explosive nature of jet fuel. This October, researchers at Caltech and JPL discovered a polymeric fuel additive that can reduce the intensity of postimpact explosions that occur during accidents and crashes. Preliminary results show that the additive can provide this benefit without adversely affecting fuel performance. The polymer works by inhibiting "misting"—the process that causes fuel to rapidly disperse and easily catch fire—under crash conditions.
Credit: Spencer Kellis/Caltech

Controlling a Robotic Arm with a Patient's Intentions

When you reach for a glass of water, you do not consciously think about moving your arm muscles or grasping with your fingers—you think about the goal of the movement. This May, by implanting neural prosthetic devices into the posterior parietal cortex (PCC)—the region of the brain that governs intentions for movement—rather than the motor cortex, which controls movement, Caltech researchers enabled a paralyzed patient to more smoothly and naturally control a prosthetic limb. In November, the researchers showed that there are individual neurons in the PPC that encode for entire hand shapes, such as those used for grasping or gesturing.

 

Caltech Scientists Develop Cool Process to Make Better Graphene

Graphene is an ultrastrong and conductive material made of a single layer of carbon atoms. While it is a promising material for scientific and engineering advances, manufacturing it on an industrially relevant scale has proven to be impractical, requiring temperatures of around 1,800 degrees Fahrenheit and long periods of time. A new technique invented at Caltech allows the speedy production of graphene—in just a few minutes—at room temperatures. The technique also produces graphene that is stronger, smoother, and more electrically conductive than normally produced synthetic graphene.
Credit: Rafael A. García (SAp CEA), Kyle Augustson (HAO), Jim Fuller (Caltech) & Gabriel Pérez (SMM, IAC), Photograph from AIA/SDO

Astronomers Peer Inside Stars, Finding Giant Magnets

Before this October, astronomers have only been able to study the magnetic fields of stars on the stellar surfaces. Now, using a technique called asteroseismology, scientists were able to probe the fusion-powered hearts of dozens of red giants (stars that are evolved versions of our sun) to calculate the magnetic field strengths inside those stars. They found that the internal magnetic fields of the red giants were as much as 10 million times stronger than Earth's magnetic field. Magnetic fields play a key role in the interior rotation rate of stars, which has a dramatic effect on how the stars evolve.
Credit: Chan Lei and Keith Schwab/Caltech

Seeing Quantum Motion

To the casual observer, an object at rest is just that—at rest, motionless. But on the subatomic scale, the object is most certainly in motion—quantum mechanical motion. Quantum motion, or noise, is ever-present in nature, and in August, Caltech researchers discovered how to observe and manipulate that motion in a small device. By creating what they called a "quantum squeezed state," they were able to periodically reduce the quantum fluctuations of the device. The ability to control quantum noise could one day be used to improve the precision of very sensitive measurements.
Credit: Ali Hajimiri/Caltech

New Camera Chip Provides Superfine 3-D Resolution

3-D printing can produce a wide array of objects in relatively little time, but first the printer needs to have a blueprint of what to print. The blueprints are provided by 3-D cameras, which scan objects and create models for the printer. Caltech researchers have now developed a 3-D camera that produces the highest depth-measurement accuracy of any similar device, allowing it to deliver replicas of an object to be 3-D printed within microns of similarity to the original object. In addition, the camera, known as a nanophotonic coherent imager, is inexpensive and small.
Credit: Image provided courtesy of Joint Center for Artificial Photosynthesis; artwork by Darius Siwek.

One Step Closer to Artificial Photosynthesis and 'Solar Fuels'

Plants are masters of photosynthesis—the process of turning carbon dioxide, sunlight, and water into oxygen and sugar. Inspired by this natural and energy-efficient process, Caltech researchers have created an "artificial leaf" that takes in CO2, sunlight, and water to produce hydrogen fuels. This solar-powered system, one researcher says, shatters all of the combined safety, performance, and stability records for artificial leaf technology by factors of 5 to 10 or more.
Credit: Santiago Lombeyda and Robin Betz

Potassium Salt Outperforms Precious Metals As a Catalyst

Rare precious metals have been the standard catalyst for the formation of carbon-silicon bonds, a process crucial to the synthesis of a host of products from new medicines to advanced materials. However, they are expensive, inefficient, and produce toxic waste byproducts. This February, Caltech researchers discovered a much more sustainable catalyst in the form of a simple potassium salt that is one of the most abundant metals on Earth and thousands of times less expensive than other commonly used catalysts. In addition, the potassium salt is much more effective at running challenging chemical reactions than state-of-the-art precious metal complexes.
Credit: Qi Zhao/National University of Singapore

Probing the Mysterious Perceptual World of Autism

The way in which people with autism spectrum disorder (ASD) perceive the world is unique. It has been a long-standing belief that people with ASD often miss facial cues, contributing to impaired social interaction. In a study published in October, Caltech researchers showed 700 images to 39 subjects and found that people with ASD pay closer attention to simple edges and patterns in images than to the faces of people. The study also found that subjects were strongly attracted to the center of images—regardless of what was placed there—and to differences in color and contrast rather than facial features. These findings may help doctors diagnose and more effectively treat the different forms of autism.
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The year 2015 proved to be another groundbreaking year for research at Caltech. From seeing quantum motion, to reconfiguring jellyfish limbs, to measuring stellar magnetic fields, researchers continued to ask and answer the deepest scientific questions.

In case you missed any of them, here are 15 stories highlighting a few of the discoveries, methods, and technologies that came to life at Caltech in 2015.

Written by Lori Dajose

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Simulation Shows Key to Building Powerful Magnetic Fields

When certain massive stars use up all of their fuel and collapse onto their cores, explosions 10 to 100 times brighter than the average supernova occur. Exactly how this happens is not well understood. Astrophysicists from Caltech, UC Berkeley, the Albert Einstein Institute, and the Perimeter Institute for Theoretical Physics have used the National Science Foundation's Blue Waters supercomputer to perform three-dimensional computer simulations to fill in an important missing piece of our understanding of what drives these blasts.  

The researchers report their findings online on November 30 in advance of publication in the journal Nature. The lead author on the paper is Philipp Mösta, who started the work while a postdoctoral scholar at Caltech and is now a NASA Einstein Fellow at UC Berkeley.

The extremely bright explosions come in two varieties—some are a type of energetic supernovae called hypernovae, while others are gamma-ray bursts (GRBs). Both are driven by focused jets formed in some collapsed stellar cores. In the case of GRBs, the jets themselves escape the star at close to the speed of light and emit strong beams of extremely energetic light called gamma rays. The necessary ingredients to create such jets are rapid rotation and a magnetic field that is a million billion times stronger than Earth's own magnetic field.

In the past, scientists have simulated the evolution of massive stars from their collapse to the production of these jet-driven explosions by factoring unrealistically large magnetic fields into their models—without explaining how they could be generated in the first place. But how could magnetic fields strong enough to power the explosions exist in nature?

"That's what we were trying to understand with this study," says Luke Roberts, a NASA Einstein Fellow at Caltech and a coauthor on the paper. "How can you start with the magnetic field you might expect in a massive star that is about to collapse—or at least an initial magnetic field that is much weaker than the field required to power these explosions—and build it up to the strength that you need to collimate a jet and drive a jet-driven supernova?"

For more than 20 years, theory has suggested that the magnetic field of the inner- most regions of a massive star that has collapsed, also known as a proto-neutron star, could be amplified by an instability in the flow of its plasma if the core is rapidly rotating, causing its outer edge to rotate faster than its center. However, no previous models could prove this process could strengthen a magnetic field to the extent needed to collimate a jet, largely because these simulations lacked the resolution to resolve where the flow becomes unstable.


Magnetic field amplification in hypernovae
Supercomputer visualization of the toroidal magnetic field in a collapsed, massive star, showing how in a span of 10 milliseconds the rapid differential rotation revs up the stars magnetic field to a million billion times that of our sun (yellow is positive, light blue is negative). Red and blue represent weaker positive and negative magnetic fields, respectively. Credit: Philipp Mösta

Mösta and his colleagues developed a simulation of a rapidly rotating collapsed stellar core and scaled it so that it could run on the Blue Waters supercomputer, a powerful supercomputer funded by the NSF located at the National Center for Supercomputing Applications at the University of Illinois. Blue Waters is known for its ability to provide sustained high-performance computing for problems that produce large amounts of information. The team's highest-resolution simulation took 18 days of around-the-clock computing by about 130,000 computer processors to simulate just 10 milliseconds of the core's evolution.

In the end, the researchers were able to simulate the so-called magnetorotational instability responsible for the amplification of the magnetic field. They saw—as theory predicted—that the instability creates small patches of an intense magnetic field distributed in a chaotic way throughout the core of the collapsed star.

"Surprisingly, we found that a dynamo process connects these patches to create a larger, ordered structure," explains David Radice, a Walter Burke Fellow at Caltech and a coauthor on the paper. An early type of electrical generator known as a dynamo produced a current by rotating electromagnetic coils within a magnetic field. Similarly, astrophysical dynamos generate currents when hydromagnetic fluids in stellar cores rotate under the influence of their magnetic fields. Those currents can then amplify the magnetic fields.

"We find that this process is able to create large-scale fields—the kind you would need to power jets," says Radice.

The researchers also note that the magnetic fields they created in their simulations are similar in strength to those seen in magnetars—neutron stars (a type of stellar remnant) with extremely strong magnetic fields. "It takes thousands or millions of years for a proto-neutron star to become a neutron star, and we have not yet simulated that. But if you could transport this thing thousands or millions of years forward in time, you would have a strong enough magnetic field to explain magnetar field strengths," says Roberts. "This might explain some fraction of magnetars or a particular class of very bright supernovae that are thought to be powered by a spinning magnetar at their center."

Additional authors on the paper, "A large-scale dynamo and magnetoturbulence in rapidly rotating core-collapse supernovae," are Christian Ott, professor of theoretical astrophysics; Erik Schnetter of the Perimeter Institute for Theoretical Physics, the University of Guelph, and Louisiana State University; and Roland Haas of the Max Planck Institute for Gravitational Physics in Potsdam-Golm, Germany. The work was partially supported by the Sherman Fairchild Foundation, by grants from the NSF, by NASA Einstein Fellowships, and by an award from the Natural Sciences and Engineering Research Council of Canada.

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How to Power Jet-Driven Supernovae
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New simulations show how a dynamo in collapsed massive stars can build the strong magnetic fields needed to power extremely energetic blasts.

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