Johns hopkins University Johns hopkins University, Summaries of Quantum Mechanics

Download Johns hopkins University Johns hopkins University and more Summaries Quantum Mechanics in PDF only on Docsity! 2012 J o h n s h o p k i n s U n i v e r s i t y Physics & Astronomy 2012 J O H N S H O P K I N S U N I V E R S I T Y P H Y S I C S A N D A S T R O N O M Y 2 0 1 2 1 Letter from the Chair Dear alumni, colleagues, and friends, One of the striking things about physics and astronomy at Johns Hopkins is the broad range of scholarship and research pursued by the members of our department. We have condensed matter physicists examining quantum phenomena in solids and pursuing microscopic understanding of familiar phenomena, such as friction; we have theorists researching large-scale structures and the early history of the universe; we have particle physicists leading the charge to analyze the exciting findings from the Large Hadron Collider; we have astronomers locating what could be the most distant galaxy ever seen; we have a team of astrophysicists and engineers developing instrumentation that will enable unprecedented new studies of cosmology and galactic evolution; and we have faculty leading a space mission science team, which produced the three most highly cited scientific papers in the world. That’s just a snapshot of the research being conducted in the department, but it illustrates the diverse expertise of our faculty and researchers. This issue of Physics & Astronomy provides an overview of some of the impressive endeavors our faculty and students have engaged in during the past year. On a sadder note, the department continues to mourn the loss of Professor Zlatko Tesanovic, who died suddenly in July of an apparent heart attack. Many of his colleagues, friends, students, and former students gathered in the Bloomberg Center in November for a touching tribute to this extraordinary man. In March 2013, we will host some of Zlatko’s colleagues from around the world for the Zlatko Tesanovic Memorial Symposium. A number of distinguished speakers will give presentations, and we will highlight Zlatko’s scientific accomplishments. A confident, esteemed academic; a gifted teacher; and a brilliant physicist, Zlatko will be deeply missed. You can read more about his work and life on page 12. I hope these pages reflect the energy and enthusiasm that is so inherent in our department. Every day I witness in our faculty and students a drive to question and learn, to teach and experience, and to explore and discover. Thank you for your interest in and support of physics and astronomy at Johns Hopkins. Best, Daniel Reich, Chair The Henry A. Rowland Department of Physics and Astronomy TABLE OF CONTENTS Letter from the Chair 1 Exploring Galaxies, Millions at a Time 2 The Slippery Physics of Friction 4 Research of Theorist Mark Kamionkowski 6 Research Briefs 8 People 11 Physics and Astronomy is an annual publication of the Johns Hopkins University Zanvyl Krieger School of Arts and Sciences Department of Physics and Astronomy. Send correspondence to: Kate Pipkin, 3400 N. Charles Street, Wyman 500W, Baltimore, MD 21218 or kpipkin@jhu.edu. Editor Kate Pipkin Managing Editor Ian Mathias Photography James T. VanRensselaer and Will Kirk, Homewood Photography (unless otherwise noted) On the cover: Created by Johns Hopkins research scientist Miguel Aragón-Calvo, the image is part of a larger computer-generated illustration that depicts streams of matter delineating a network of cosmic voids, each tens of millions of light years across. This particular section shows how most matter in the universe is located in a complex network of walls, filaments, and clusters. We see the individual voids as membranes, each designated with a different color. This page: The streams in this figure illustrate the close relation between the geometry and the dynamics of the cosmic web as matter moves from under-dense voids onto increasingly dense walls, filaments, and clusters. Aragón-Calvo’s poster, made in conjunction with Julieta Aguilera and Mark SubbaRao PhD ’97 from the Adler Planetarium, was awarded first place in the informational graphics category in the 2011 NSF International Science & Engineering Visualization Challenge. Aragón-Calvo is part of Johns Hopkins Institute for Data Intensive Engineering and Science, aimed at developing new ways of building and analyzing huge data sets. See a detailed view of this poster on the web at zoom.it/Boj2 6 J O H N S H O P K I N S U N I V E R S I T Y P H Y S I C S A N D A S T R O N O M Y 2 0 1 2 J O H N S H O P K I N S U N I V E R S I T Y P H Y S I C S A N D A S T R O N O M Y 2 0 1 2 7 Is Marc Kamionkowski a particle physi- cist, an astrophysicist, or a cosmologist? “I’m a theorist,” says Kamionkowski. In the 2011-12 academic year, his first at Johns Hopkins, he has published papers on gravitational waves, cosmic accel- eration, dark matter, and particle decay—a remarkable discipline-bridging assortment of research. “When you’re a theorist in physics, you can jump around to different areas. You don’t have to wait for the satellite to launch, or for the collider or telescope to be built.” That’s not to say Kamionkowski is unin- terested in what experimentalists learn from their satellite missions, telescope observa- tions, and collider experiments—quite the contrary, in fact. Previously the Robinson Professor of Theoretical Physics and As- trophysics at the California Institute of Technology, Kamionkowski sees his role as tightly linked to experiments in cosmology, astrophysics, and particle physics. “My job is to keep an eye on a bunch of unrelated fields, synthesize and amalgamate results from different areas, and provide feedback in the form of suggestions for new experiments that would answer questions that remain.” Although Kamionkowski’s graduate research had been on the nature of dark mat- ter, an area where he is still active, as a post- doc he developed an interest in the cosmic microwave background (CMB) results com- ing out of the Cosmic Background Explorer satellite, or COBE. COBE established that the CMB radiation released around 380,000 years after the Big Bang—the so-called “time of last scattering”—is anisotropic, or non- uniform, giving us critical information about the evolution of the large-scale structure we see in our universe today. Kamionkowski and some of his colleagues published a series of papers suggesting fur- ther measurements that could map the CMB with enough precision to answer long-stand- ing questions about the geometry of the uni- verse. These papers helped make the case for the Wilkinson Microwave Anisotropy Probe, or WMAP, which was led by JHU physicist Charles Bennett (who had also been a key figure behind COBE) and launched in 2001, sooner than anyone expected. “We thought it would take several decades for this experi- ment to be carried out,” says Kamionkowski. Beyond confirming that the universe is flat (Euclidean) to an order of magnitude of greater precision than before, WMAP pro- vided strong support for previous observa- tions made of distant supernovae, which had shown that the expansion of the universe is accelerating. More broadly, WMAP is cred- ited with ushering in the era of “precision cosmology,” and establishing the field as a core subject within physics and astronomy. “Cosmology used to be the butt of every- one’s jokes,” says Kamionkowski. “Now it’s a paradigm of how quantitative science should be done. I take pride in being one of the people who motivated this transformation.” Pushing precision cosmology even further, Kamionkowski and colleagues have suggested a way to peer beyond the CMB into the very earliest moments of the uni- verse. They proposed that the polarization of radiation coming from the CMB could be used to look for gravitational wave signals from the first tiny fractions of a second after the Big Bang—the period of rapid expan- sion known as inflation. Previously, these signals had been thought to be too small to be observed, but Kamionkowski’s papers stimulated a number of research efforts. “Experimentalists picked up on this faster than I had anticipated,” says Kamionkowski, “and the idea of inflation started to seem like it could be a little less crazy.” Alongside his work on the early universe, Kamionkowski continues to probe the nature of dark matter, which accounts for around 23 percent of the energy in the universe. Most cosmologists concur that dark matter must be an as-yet undiscovered particle, and Kamionkowski is in the camp that believes this particle will turn out to be described by the theory supersymmetry, which was devel- oped to answer some of the questions that emerged from the Standard Model of par- ticle physics. Kamionkowski’s earlier research showed that quantum mechanics places an upper limit on the mass of a supersymmet- ric dark matter particle; this limit suggests that the particle’s mass should be accessible by the Large Hadron Collider (LHC). His more recent work has helped guide particle collider, cosmic ray, and neutrino experi- mentalists in looking for the signatures of these thus-far unobserved particles. Unsurprisingly, the searches for dark matter and supersymmetry are among the hottest topics in particle physics today, and many believe the LHC has a shot at provid- ing us the answer—especially now that it may have delivered the long sought Higgs boson. “We used to say that if the Higgs is discovered, that proves supersymmetry exists; and if supersymmetry exists, the lightest supersymmetric particle should be the dark matter,” says Kamionkowski. “[We now have reason to believe] the Higgs exists, but it’s still a pretty tenuous argument. We would like to see the lightest supersymmetric particle observed at the LHC.” Whether the LHC will reveal dark matter and super- symmetry remains to be seen. “You never know. If we did, we wouldn’t need to do the experiment.” While the LHC experiment continues, Kamionkowski forges ahead in his own “lab”—which mostly consists of a desk, paper, and pencils. “I’m actually one of the last of my generation to still make a living with paper and pencil,” he says. “Sometimes I work on projects involving simulations, but I’m not a simulator. I like to think of myself as an idea-oriented pencil-and-paper theorist.” For someone with the wide-ranging curiosity and talents of Marc Kamion- kowski, the diverse and high-powered Department of Physics and Astronomy at the Krieger School is an ideal place to work. “There are a lot of exciting things going on in physics and astrophysics at Johns Hopkins,” he says. “There are really smart people, creative people, people who know how to get things done. This depart- ment is smaller than some of the places it competes with, but it looms large. When you put it together with the Space Tele- scope Science Institute, it’s a great place to be. The trajectory is extremely positive.” Research of Theorist Marc Kamionkowski Spans Many Fields BY GABRIEL POPKIN 8 J O H N S H O P K I N S U N I V E R S I T Y P H Y S I C S A N D A S T R O N O M Y 2 0 1 2 J O H N S H O P K I N S U N I V E R S I T Y P H Y S I C S A N D A S T R O N O M Y 2 0 1 2 9 no one would have guessed that in 1962, rare earth metals would be- come a staple of modern living in less than 50 years time. Likewise, few would have guessed that 31-year-old physicist Brian Judd was on the verge of publish- ing seminal research on rare earth metals that his colleagues would cite well into the 21st century—becoming more popular and relied upon as decades came and went.    Brian Judd became fascinated by the rare earth ions in crystalline materials or liquids while studying at Oxford in the 1950s. He was particularly interested in the paramagnetic resonance of these 15 elements’ electrons, an effect akin to the nuclear magnetic resonance used in medical imaging devices.  The study of rare earth metals was advanc- ing thanks in part to interest in crystals stimu- lated by radar and microwave research. But these metals and their ions were still puzzling researchers because, despite their similarities, they produced strikingly different signatures when analyzed with a spectrograph. “They were just a big mystery,” says Judd, the Gerhard H. Dieke Professor Emeritus in the Department of Physics and Astronomy. And few researchers have done more to try to unravel that mystery than he has. As late as the early 1960s, physicists struggled to find a mathematical language to describe the behavior of these elements at the sub-atomic level, where classical physics breaks down and quantum theory takes over. What no one knew 50 years ago was that one day rare earth doped materials would  play a crucial role in fiber optic com- munications, and make it possible to produce miniaturized electronic components for every- thing from laptop computers and mobile phones to hybrid cars and lasers. Judd’s key scientific contribution to the field came in 1962, when he published a paper titled “Optical Absorption Intensities of Rare-Earth Ions,” that proposed a mathemati- cal method for predicting how the f electrons in rare earths behave when they jump from one energy level to another while orbiting the atom’s nucleus. Judd, then at the University of California at Berkeley, used the mathematical theory of Lie groups to simplify the calculations needed to describe the behavior of rare earth electrons, without sacrificing accuracy. His paper was published the same day as a structurally similar work on f electrons by George Ofelt, a graduate student of Brian Wybourne at Johns Hopkins Univer- sity, which did not include Judd’s detailed numerical comparisons between theory and experiment for the radiation intensi- ties of the electrons. The approach came to be known as the Judd-Ofelt Theory. “The reason that the article I wrote was so successful was that it dealt directly with ex- periment,” Judd, now 81, said in an interview. “I remember that the British physicist Maurice Pryce told me never to get seduced by the mathematics. It’s very easy to be first of all amazed by how the mathematics is beautiful in a funny kind of way, by the surprises you get when you work out the mathematics.   “But Pryce said, ‘Never be seduced.’ And in fact when I wrote the article it was strictly calculations with the idea of describing only what an experimentalist would find useful.” The Judd-Ofelt Theory quickly became a standard work, frequently cited in papers by other researchers. Its citation rate ac- celerated sharply in the early 1990s, after the invention of erbium-doped optical fiber amplifiers, critical for long-range optical fiber communications, and is  now be- ing referenced over 200 times per year. In August, Judd and Ofelt were hon- ored at a chemistry and physics confer- ence in Udine, Italy, where a series of speakers celebrated the 50th anniver- sary of the publication of their work. “It’s really defined the whole field for the people who study the spectroscopy of these rare earth elements,” says Dan- iel Reich, chair of the department. The late physicist Brian Wybourne, who studied rare earth elements at Hopkins in the early 1960s, wrote in 2004 that the Judd-Ofelt papers “represent a paradigm that has dominated all further work on the intensities of rare earth transitions in solu- tions and solids up to the present time.” Judd came to Hopkins in 1966, not long af- ter authoring his groundbreaking research pa- per, and he would remain on the Homewood campus for the rest of his career. Today he is retired and living in Baltimore with his wife, Josephine Gridley, but keeps in touch with his former graduate students and maintains an office at the Homewood campus. Even in retirement, Judd remains fascinat- ed by the mathematical challenges posed by elements 57 through 71 of the periodic table. “There’s a whole pile of mysteries, to my mind, in the mathematics of rare earths,” he said. “Everything can be calculated according to quantum mechanics. And everything works out well.” But certain complicated electron configurations produce results that still puzzle him, and he is still trying to understand them. “If you get too interested in the mathemat- ics, you can spend a lifetime working it out,” he says. “And in fact that’s what happened to me. I’ve become seduced by the mathematics.” —Doug Birch  Brian R. Judd, Gerhard H. Dieke Professor Emeritus Assistant Professor N. Peter Armitage makes adjustments to the new helium reliquefier system. Department Responds to Global Helium Shortage RESEARCH BRIEFS Milestone: The Judd-Ofelt Theory Turns 50 WMAp team scores Big with Gruber Cosmology prize and World’s Most Cited papers professor Charles Bennett and the Wilkinson Microwave Anisotropy Probe (WMAP) space mission science team were awarded this year’s Gruber Cosmology Prize. Bennett and the 26-member WMAP team were recognized for their unprece- dented study of ancient light dating back to the infant universe. The WMAP team, led by Bennett, was able to determine a much more precise age, shape, compo- sition, and history of the universe. The WMAP team also discovered that the first stars formed when the universe was only about 400 million years old. The annual Gruber Cosmology Prize recognizes “fundamental advances in our understanding of the universe.” It is co-sponsored by the Gruber Foundation and the International Astronomical Union and aims to acknowledge and encourage further exploration. “It is tremendously exciting to be recognized with the Gruber Cosmology Prize,” says Bennett, the Alumni Centen- nial Professor of Physics and Astronomy. “I have been very fortunate to work with the talented and fine people of the WMAP team, and I am particularly delighted that our entire science team has been hon- ored with this prestigious award.” Bennett and the team shared the $500,000 prize, and Bennett was given a gold medal in August at the International Astronomical Union meeting in Beijing. In addition to winning the Gruber Cosmology Prize, the research conducted by Bennett and the WMAP team resulted in production of the three most highly cited scientific papers in the world in 2011, according to Thomson Reuters’ Science Watch. Papers from the WMAP mission have made it to the top of the list in previous years (2003, 2007, 2009), but this is the first time they have taken the top three spots. early in the fall semester, researchers and faculty members installed a helium recovery system and liquefier in the Bloomberg Center. Condensed matter physicists and astronomers in the department use liquefied helium to create extremely cold research conditions (often just a few degrees above absolute zero). When helium gas is released into the air, whether from a party balloon or from liquid helium vaporized in a research cryostat, it dissipates into the atmosphere, never to be utilized again. The new system, which captures used helium from labs throughout the department and then purifies and re-cools it back to the liquid state, serves as a much-needed recycler of this non- renewable resource. It can store 500 liters of liquid helium. “The liquefier delivers helium to researchers at a greatly reduced cost,” explains Assistant Professor N. Peter Armitage, who spearheaded the liquefier’s acquisition and installation. “The price of helium had increased about 30 percent in the five years or so leading up to when we decided to buy a liquefier last year, and the price has gone up about another 40 percent just in this year alone. And we can’t even get it reliably. Helium is becoming more expensive and less available.” The current scarcity of helium could have significant implications for the space, high-tech, and medical industries. “It’s just wasteful not to have a liquefier,” says Armitage. The liquefier creates a nearly closed loop of helium usage within Bloomberg, and by enabling a stable and affordable supply of liquid helium for the department, it will provide critical infrastructure for research from superconductivity and nanoscience to cosmology for years to come. 10 J O H N S H O P K I N S U N I V E R S I T Y P H Y S I C S A N D A S T R O N O M Y 2 0 1 2 J O H N S H O P K I N S U N I V E R S I T Y P H Y S I C S A N D A S T R O N O M Y 2 0 1 2 11 tyrel McQueen recently garnered the 2012 David and Lucile Packard Foundation Fellowship for Science and Engineering. Just 16 Packard Fellowships are awarded annually, each honoring young scientists with unusually creative research interests. McQueen, a dual appointment in the Department of Physics and Astronomy and the Department of Chemistry, will use the fellowship’s $875,000 stipend to further his unique interdisciplinary research: discovering, designing, and controlling materials with exotic electronic states of matter. Applications for such study are wide-ranging, from fundamental science to solving complex energy problems. “I’m excited to see generous support for new materials synthesis and solid state chemistry,” says McQueen, “and the flexibility offered by these unrestricted funds will be invaluable to my research team as we pursue exotic new quantum phenomena in electronic materials.” “The Krieger School is enormously proud of the accomplishments of Professor McQueen, and we look forward eagerly to the discoveries he will provide in the years to come,” adds Dean Katherine Newman. “I have had the personal pleasure of hearing him lecture undergraduates on his work, and he conveys the kind of excitement that we want budding scientists to hear. We are grateful to the Packard Foundation for recognizing this rising star.” Chia-Ling Chien, the Jacob L. Hain Professor, has won the 2012 Asian Union of Magnetics Societies Award. Given once every two years to researchers from AUMS member countries, the award honors Chien’s significant contributions to magnetics research. In particular, the union cited Chien’s “seminal contribution to magnetic materials, nanostructures, magnetoelectronic phenomena, and devices.” Research scientists Mark neyrinck (left) and Miguel Aragón-Cavalo won a New Frontiers in Astronomy & Cosmology award for their work combining origami concepts with measurements of the universe’s shape and complexity. Neyrinck and Aragón-Cavalo will use the prize money to construct the first all-inclusive quantitative measurement of the entropy of the cosmic web—the cellular, web- like arrangement of galaxies in the universe that shares concepts and methodologies with origami and paper-folding. The award is funded by the John Templeton Foundation. Brice Ménard was selected by the Maryland Academy of Sciences as the Outstanding Young Scientist of 2012. The award was established in 1959 to recognize and celebrate the extraordinary contributions of young Maryland researchers across all fields of science. Ménard was recognized for his research in extragalactic astrophysics and cosmology. Ménard also won the 2012 Sloan Research Fellowship to support his research on extragalactic astrophysics and cosmology. The Sloan Fellowship honors early-career scholars with outstanding promise with two-year $50,000 grants, which Ménard will use to continue developing new techniques of mining large astronomical data sets. His work using such techniques has already led to the “We do not yet know where it will lead us. But it may have profound implications.” —andrei Gritsan, associate Professor PEOPLE Gardner Fellow Studies Quasar Spectra When he began graduate studies in 2011, ting-Wen Lan didn’t imagine he would win the department’s sought-after Gardner Fellowship. In fact, he didn’t know he was eligible. Having just arrived from Taiwan, Lan focused on his study of astronomy (and, when there was time, the English language). But in one of his first courses, Observa- tional Astronomy, Lan caught the attention of Assistant Professor Brice Ménard, who co-taught the course with Assistant Professor Nadia Zakamska. “For the final part of his semester project, Ting-Wen had to estimate how many quasars from the Sloan Digital Sky Survey (SDSS) should be spectroscopically Faculty and Students Instrumental in LHC Breakthrough Members of the department played important roles in this summer’s discovery of a new particle that contains qualities consistent with the Higgs boson—arguably the most important particle physics breakthrough in decades. For most of 2012, Associate Professor Andrei Gritsan, post-doctoral fellow Sara Bolognesi, and graduate student Andrew Whitbeck traveled back and forth from Baltimore to the Large Hadron Collider (LHC) in Geneva, Switzerland. The trio was part of a large, world-wide team of physicists working on the Compact Muon Solenoid (CMS), one of two massive particle detectors used to analyze the LHC’s proton-proton collisions in the search for the long-predicted Higgs boson. Gritsan and his team focused their search for the Higgs boson on a specific form of decay of the Higgs into two Z bosons. They developed an array of very specific variables designed to indicate the presence of a new particle over the course of billions of individual collisions. And the presence of a new particle is precisely what they and their colleagues found. But what particle? Much more research is needed to identify the new particle and confirm if it is, in fact, the Higgs boson. Such a confirmation would help explain how massless particles acquired mass in the very early history of the universe and add more legitimacy to the Standard Model. “We do not yet know where it will lead us,” explains Gritsan, who has been working at the LHC since 2005. “But it may have profound implications.” Regardless of the particle’s true identity, Gritsan, Bolognesi, and Whitbeck contributed to its discovery and were front-and-center at the LHC during the exciting early days of July, when the revelation was announced. “It was a huge discovery that will influence my research for the rest of my career,” says Whitbeck.  Faculty Members Receive Prestigious Fellowships and Awards detection of gravitational magnification by dark matter around galaxies, the discovery of tiny grains of dust in the intergalactic space, and a better understanding of how light rays propagate throughout the universe. Ménard’s fellowship marks back-to-back Sloan awards for the department: nadia Zakamska was awarded the Sloan Fellowship in 2011 for her research with Earth and space-based telescopes and large data sets. © 2 01 2 CE RN