Wednesday, September 24, 2014

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Wednesday, September 10, 2014
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Superstring Theorist Honored with Science Writing Prize

Theoretical physicist and superstring expert Hirosi Ooguri, Caltech's Fred Kavli Professor of Theoretical Physics and Mathematics and founding director of the Walter Burke Institute for Theoretical Physics, has been selected to receive the Kodansha Prize for Science Books, Japan's only major prize for science books, for his popular science work, Introduction to Superstring Theory.

Superstring theory is considered the leading candidate for the ultimate unified theory of the forces and matters in nature, and Ooguri's Japanese-language book offers the general reader a "clear explanation of the essence of the theory," notes Nobel Laureate Makoto Kobayashi, who served on this year's award jury.

Ooguri will receive the award, which comes with a cash prize of approximately $10,000, at a ceremony to be held on September 19, 2014, at the Tokyo Kaikan, adjacent to the Imperial Palace.

"I am honored to receive such a prestigious prize, and I am particularly delighted by the fact that the location of the award ceremony, the Tokyo Kaikan, is where I received the Nishina Memorial Prize five years ago for my research on topological string theory"—research that is also described in Introduction to Superstring Theory. "As a scientist, it is particularly rewarding to be honored twice, once for the original research and this second time for the popular science book conveying the research to general public."

Introduction to Superstring Theory is the final installment in Ooguri's Trilogy on Forces in Nature; the series, which also includes What is Gravity? and Strong Force and Weak Force, has sold a quarter of a million copies in Japan in the last two years.

"Fundamental research may not immediately lead to profit, and support by the society is essential," Ooguri says. "With this book, I tried to return my gratitude to society. It is particularly gratifying to receive letters from high school students saying that the book inspired their interests in science."

In addition to the Nishina Memorial Prize, Ooguri has also been awarded the Leonard Eisenbud Prize for Mathematics and Physics from the American Mathematical Society, the Humboldt Research Award in Physics, and the Simons Investigator Award in Physics. He is a Fellow of the American Mathematical Society, a trustee of the Aspen Center for Physics, and a principal investigator of the Kavli Institute for the Physics and Mathematics of the Universe at the University of Tokyo.

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Quantum Information Meets Condensed Matter: Inside the Mind of Xie Chen

Perhaps you have heard of Schrödinger's cat, a fictional feline created by physicist Erwin Schrödinger as a thought experiment in 1935. According to her inventor, Schrödinger's cat can be simultaneously alive and dead inside a sealed box, although upon an observer's opening the box, the cat will always be found either alive or dead.

If you are among the quantum confused—those who think Schrödinger was engaged in some serious crazy talk when he invented his dead-and-alive superposed cat—take heart. You are in good company. Xie Chen, who joined the Caltech faculty as an assistant professor of theoretical physics on July 1, admits that she too finds quantum properties of matter, like superposition and entanglement, counterintuitive . . . though impressively congruent with experimental results.

Chen comes to Caltech after a two-year postdoctoral fellowship at UC Berkeley. Originally from China, Chen received her BS from Tsinghua University in Beijing and her PhD from MIT. She recently discussed with us her research interests and ambitions for her Caltech career.

What will you be working on at Caltech?

I'm a theoretical physicist, and I work in both condensed matter and quantum information. Work at this intersection is being pursued here at Caltech in the physics, math, and astronomy division, and also through IQIM [the Institute for Quantum Information and Matter]. It's a new trend to bring these two areas of theoretical study together.

What is quantum information?

At the heart of quantum information is the idea that computers or cell phones, and the computation and communication protocols through which they operate, can run more efficiently and securely if we make use of the quantum properties of matter. For example, if a cell phone's hardware relies on the quantum behavior of its components, it will be possible to develop encryption protocols that, at least theoretically, are totally secure.

When did you first become interested in quantum information?

My interest started in college, and it was the focus of the first part of my graduate study. My goal was to devise ways to make quantum computing more resistant to noise, such as heating or the effect of stray electromagnetic fields from the environment. The quantum properties of things can be so fragile. If you raise the temperature a little bit or have a little disturbance in your lab, that could cause a quantum computer to break down. This has been bothering people for the last 20 years. The principle of quantum computation is well established, but the conditions to make it work in the lab are just not there. This continues to be a big part of my work: making quantum computation more reliable and more resistant to noise.

How do quantum information and condensed matter relate to one another?

Condensed matter is a much older and broader topic in physics. Analyzing the properties of solid and liquid materials—particularly things like semiconductivity, superconductivity, and magnetism—has been around for hundreds of years. I shifted into it in the second half of my graduate study, as people began to realize that ideas about quantum information could be very helpful in the study of condensed matter.

That need came out of the laboratory: peculiar quantum properties of condensed matter were appearing in the lab and people wanted to understand them. Previously, classical physics or simple quantum theories were able to account for everything that was seen in condensed matter. However, with modern technologies it's now possible to access and observe the quantum aspects of materials at a deeper level. For example, strange conducting materials were found which do not allow current to flow through the interior but only on the surface of the material with precisely quantized conductance. Conventional methods cannot explain such a topological property of the material. We need new methods to explain that observation. This is where quantum information ideas are very useful.

Quantum properties are so counterintuitive for the average person. Does that change when you're immersed in quantum physics on a daily basis, as you are?

No. Quantum mechanics has never fully become part of my intuition. I think that people still haven't truly understood the quantum level yet. The quantum community generally takes the attitude that we can set those questions aside for a while, because quantum theory predicts experimental results so well. But if you think deeply enough about quantum reality, and sometimes I do, you get confused. There are so many fundamental questions that we cannot yet fully explain. The quantum level is more a mathematical formulation than an intuition we are born with, because we mostly deal with the classical world.

But if technologies are developed that rely on quantum properties, do you think that will change—that we will start to internalize a quantum view of things?

Eventually, maybe. When we deal with the quantum world frequently enough and have reached a better consensus on how to interpret it, it may be possible to develop a quantum intuition of the world. That would be an amazing state of mind to have, because with it we could not only push science forward but also have a totally new perspective on the universe and the meaning of life!

What are you looking forward to at Caltech?

Putting "quantum" and "materials" together isn't easy and it's an amazing subject that's developing quickly as people are trying to figure out what's going on. With IQIM and all the specialized faculty here, Caltech is a leader in this. People on the quantum side and the materials side talk to each other and work on projects together at Caltech. I'm very excited to be a part of that.

Cynthia Eller
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Quantum Information Meets Condensed Matter
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Sean Carroll Brings Physics to the Masses

Sean Carroll, a senior research associate in physics at Caltech, has won the 2014 Andrew Gemant Award from the American Institute of Physics. The award honors "significant contributions to the cultural, artistic, or humanistic dimensions of physics"—in Carroll's case, "extraordinary public outreach on particle physics and cosmology . . . and for his pioneering work communicating with a variety of international audiences using social networking."

"Science should be part of the regular conversation that people have over dinner, along with sports and movies and politics," Carroll says. "The universe belongs to everybody, and we can all share in the quest to understand it."

Between blogging, tweeting, appearing on The Colbert Report and NOVA, and writing books chronicling the hunt for the Higgs boson or exploring why time only flows in one direction, Carroll spends his days as a theoretical physicist coming up with alternative theories of gravity and constructing mathematical models of the interactions between the ordinary matter that we perceive and the unseen "dark matter" and "dark energy" that, taken together, are believed to account for 95 percent of the universe's mass.

Previous awardees include Edwin Krupp, director of Los Angeles's Griffith Observatory; Paula Apsell, senior executive producer of NOVA; and Stephen Hawking.

Carroll will receive the award on January 5, 2015 at the Reuben H. Fleet Science Center in San Diego's Balboa Park and deliver a public lecture.

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50 Years of Quarks

A Milestone in Physics

Caltech's Murray Gell-Mann simplified the world of particle physics in 1964 by standing it on its head. He theorized that protons—subatomic particles as solid as billiard balls and as stable as the universe—were actually cobbled together from bizarre entities, dubbed "quarks," whose properties are unlike anything seen in our world. Unlike protons, quarks cannot be separated from their fellows and studied in isolation; despite this, our understanding of the universe is built on their amply documented existence.

These days, the subatomic particle catalog has hundreds of entries. Back in the 1920s, there were only two—the massive proton, which had a charge of +1 and was found in the atom's nucleus; and the electron, which had very little mass, a charge of –1, and orbited the nucleus. Every proton occupied one of two possible "spin states" in relation to the surrounding space. These spins could easily be flipped in a behavior described by a mathematical construct called the SU(2) symmetry group. "Quantum spin states do not have a familiar analog in everyday experience," says Caltech's Steven Frautschi, professor of theoretical physics, emeritus. "However, they can be turned into one another by 180-degree rotations in ordinary space, which is what SU(2) does." 

In 1932, the neutron was discovered. This new particle appeared to be the proton's close relative—even its mass was the same, to within 0.2 percent—but the neutron had no electric charge. SU(2) symmetry in ordinary space could not account for the neutron's existence, but quantum mechanic Werner Heisenberg fixed the problem by declaring that the two particles were indeed fraternal twins . . . if you took SU(2) from another point of view. Frautschi explains: "Like rotating a physical object in ordinary space, Heisenberg extended SU(2) by rotating the symmetry group in a 'space' that quantum theorists made up." 

Heisenberg gave his rotation a quantum number, now called isospin, which described the particle's interaction with the so-called strong nuclear force. (The strong force overcomes the mutual repulsion between positively charged protons, binding them and neutrons to one another and allowing stable atomic nuclei to exist.) The mathematical treatment of isospin in Heisenberg's theoretical space was identical to that of the proton's spin in ordinary space, allowing neutrons to turn into protons and vice versa. In the physical world, Heisenberg's version of SU(2) is like a slowly spinning roulette wheel after the ball has come to rest—if the white ball (a proton) could transmute itself into a black ball (a neutron) and then back again to a white ball once every revolution.

A comprehensive theory of the strong force was published three years later by Hideki Yukawa of Osaka University. Quantum-mechanical forces need particles to carry them, and Yukawa calculated that the strong-force carriers would be much more massive than electrons but not nearly as massive as protons. Soon after, in 1937, Caltech research fellow Seth Neddermeyer (PhD '35) and Nobel laureate physics professor Carl Anderson (BS '27, PhD '30) stumbled upon a likely candidate: a new particle with about 200 times the electron's mass and about one-ninth the mass of the proton. 

Although it was widely assumed that Neddermeyer and Anderson had found the force-carrying particles that would prove Yukawa's theory, the paper announcing the discovery merely described them as "higher mass states of ordinary electrons." This proved to be the case—the new particles, now called muons, did not behave as Yukawa had predicted but instead behaved exactly like electrons. This offered the first inkling that otherwise identical particles came in multigenerational "families" of very different masses. 

The search for Yukawa's strong-force carriers did not bear fruit until 1947, when particles dubbed pions finally turned up—as did kaons, the massive second-generation members of the pion family. These kaons, however, were oddly long-lived, lasting a quadrillion times longer than expected. ("Long-lived" is relative, as the average kaon decayed into other particles in less than a millionth of a second.) 

Then, in 1953, Murray Gell-Mann, then at the University of Chicago, and Kazuhiko Nishijima (also at Osaka University) independently demystified the kaons' strange longevity by proposing yet another new quantum number to explain it. This number, imaginatively called "strangeness," permits particles possessing it to decay—but only by shedding one strangeness unit at a time. This relatively slow process created stepwise cascades of successively less-strange particles, ultimately ending in particles whose strangeness is zero.

Unfortunately, strangeness and SU(2) did not mesh mathematically. The theorists remained at an impasse; meanwhile, the experimentalists built ever-more-powerful machines that created ever-more-massive, ever-more-exotic particles whose ever-briefer existences could only be inferred by working backward from the collections of mundane particles into which they decayed. 

The mushrooming catalog of discoveries defied all attempts at organization until 1961, when Gell-Mann—who had moved to Caltech in 1955—and Israeli physicist Yuval Ne'eman independently proposed sorting particles into mini-periodic tables organized by electric charge and strangeness number. Gell-Mann dubbed his version the "Eightfold Way," after Buddhism's Eightfold Path to enlightenment, because the tables tended to contain eight members each. 

The Eightfold Way brought physicists full circle, as it proved to be a rotating SU(3) symmetry group. Just as charge had driven the isospin axis in Heisenberg's SU(2) symmetry, strangeness provided a second, perpendicular rotation. In other words, SU(2) spun only around the y axis, as it were, but SU(3) spun on both the x and y axes simultaneously. It was as if the roulette wheel had morphed into a globe spinning around the poles while the polar axis itself spun around two points on the equator. Relationships between particles could be represented as rotations in isospin, in strangeness, or in both. 

Although the Eightfold Way solved one problem, it created another. Whereas SU(2) manifests itself through doublets—the proton-neutron dichotomy—SU(3)'s hallmark is the triplet. "Nature is likely to use this fundamental representation," says physics professor Frautschi, "but there was no sign of triplets in the data." Triplets could be conjured into existence, however, if the rock-solid proton could be broken apart. In that case, SU(3)'s fundamental triplet could be a menu of three hypothetical entities, each with its own unique set of quantum numbers. 

If the menu choices were truly independent—much like allowing a diner to order an enchilada with all beans and no rice on the side, for example—a fundamental triplet offered enough possibilities to build every massive particle known, and then some. Intermediate-mass pions and kaons would contain two menu selections; protons, neutrons, and a slew of more massive particles would be three-item combos. "It's all about making patterns," Frautschi explains. "You write down sets of quantum numbers, add them up, and see what fits." 

However, the numbers refused to add up. Both the two-piece kaon and a three-piece particle called the sigma came in positive, negative, and electrically neutral versions. But if the only charges available to the triplet's members were –1, 0, and +1, no conceivable combination of choices allowed all the other quantum numbers to come out right. 

This should have been the end of the story. Robert Millikan, Caltech's first Nobel laureate, had won his prize for showing that electric charge came only in whole-numbered units. But in 1964, Gell-Mann and George Zweig (PhD '64) independently flew in the face of all that was known by proposing that the fundamental triplet had one member with a +2/3 charge and two members with charges of –1/3

Gell-Mann called the members of his triplet "quarks," after the sentence "Three quarks for Muster Mark!" in James Joyce's Finnegan's Wake. Everything found in the old SU(2) symmetry group could be fashioned from +2/3 "up" quarks and –1/3 "down" quarks, both of which had a strangeness number of zero. A proton was up-up-down, for example; a neutron was down-down-up. The other –1/3 quark had a quantum of strangeness; adding these "strange" quarks to the mix took care of the particles that SU(2) couldn't handle. Since this proposal was so heretical, Gell-Mann presented quarks as no more than an expedient accounting system, writing, "It is fun to speculate about the way quarks would behave if they were physical particles of finite mass (instead of purely mathematical entities . . . )." 

Zweig, meanwhile, called his theoretical constructs "aces," as they were put together into "deuces" and "treys" to make pions and protons. He was also less circumspect than Gell-Mann. "The results . . . seem somewhat miraculous," Zweig wrote. "Perhaps the model is . . . a rather elaborate mnemonic device. [But] there is also the outside chance that the model is a closer approximation to nature than we may think, and that fractionally charged aces abound within us." Sadly, Zweig's paper met a very different fate than Gell-Mann's. Since Zweig was working as a very junior postdoctoral fellow at CERN, the European Center for Particle Physics, all his manuscripts had to be reviewed by his superiors before publication. The senior staff considered Zweig's ideas too outré, and his paper got sent to a file room instead of a journal. He returned to Caltech soon after, joining the faculty. 

Gell-Mann went on to win the Nobel Prize for Physics in 1969—although not for the quark model per se, which was still on thin ice. (The very first experiments demonstrating that protons might contain something else had been run at the Stanford Linear Accelerator the preceding year.) Instead, he was cited "for contributions and discoveries concerning the classification of elementary particles and their interactions."

Quarks have since been shown to be physical particles with finite masses. The up quark has been found to have about half the mass of the down, while the strange quark has been shown to be some 50 times more massive—a sure sign that it represented a second generation of quarks, just as muons had turned out to be second-generation electrons. In 1974, the other second-generation quark turned up—the "charm" quark—followed three years later by the third-generation "bottom" quark. It then took nearly two decades to find what is called the "top" quark—which, as far as we know, completes the quark family tree. 

Gell-Mann was named the Robert Andrews Millikan Professor of Theoretical Physics in 1967—a fitting irony that the man who showed that fractional electric charges are necessary holds the chair named for the man who showed that electric charge is indivisible.

Gell-Mann's paper introducing the quark was all of two pages long; what has been written about quarks since then would fill warehouses. This half-century of discoveries was celebrated at a conference in the 84-year-old Gell-Mann's honor, hosted by Caltech's theoretical high-energy physics group in December, 2013.

Douglas Smith
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Ed Stone Honored

Voyager Project Scientist

Ed Stone, Caltech's David Morrisroe Professor of Physics, has won the aerospace equivalent of an Oscar. On Wednesday, July 16, the American Astronautical Society (AAS) presented him its sixth Lifetime Achievement Award for his "sustained and extraordinary contributions to America's space programs, including innovative planetary missions."

From 1991 to 2001, Stone was the director of Caltech's Jet Propulsion Laboratory, America's lead center for the robotic exploration of the solar system. (The Lab was transferred to NASA at the space agency's birth in 1958.) Among the firsts during Stone's 10-year tenure, JPL launched a successful mission to explore Saturn, its rings, and its moons; dispatched a spacecraft to visit a comet and return samples of its dust cloud to Earth; and went off-roading on Mars. The toaster-oven-sized Sojourner rover covered 100 yards in 80 days, and its six-wheeled body plan has been the standard for all Mars rovers since.

Stone is also the project scientist for JPL's Voyagers, a role he assumed during the mission's detailed design phase in 1972—five years before the twin spacecraft were launched. The two ships parted ways after setting similar courses for Jupiter and Saturn and giving us the first good look at those gas giants and their unexpectedly exotic moons. Voyager 2 continued on the Grand Tour of the outer solar system, visiting Uranus and Neptune, while Voyager 1 steered up and out of the plane of the solar system. In 2012, nearly 35 years to the day after its launch, Voyager 1 sailed beyond the reach of the solar wind and became the first man-made object to enter the interstellar void. "It's a special honor to receive this award and a privilege to have been part of Voyager's exploration of the solar system, a 37-year journey of discovery that now extends into the space between the stars," Stone says.

The AAS's Lifetime Achievement Award is presented in Washington, D.C., on every tenth anniversary of the society's founding. The first award, in 1964, went to Wernher von Braun, who created the Saturn V rocket that would take the Apollo astronauts on the moon. The second award went to JPL director William H. Pickering (BS '32, MS '33, PhD '36), who in 1958 put America's first satellite, Explorer 1, into orbit atop another of von Braun's rockets.

Douglas Smith
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