Caltech Awarded $12.6 Million for New Institute for Quantum Information and Matter

PASADENA, Calif.—The California Institute of Technology (Caltech) has been awarded $12.6 million in funding over the next five years by the National Science Foundation (NSF) to create a new Physics Frontiers Center. Dubbed the Institute for Quantum Information and Matter (IQIM), the center will bring physicists and computer scientists together to push theoretical and experimental boundaries in the study of exotic quantum states.

Every three years, the NSF selects new Physics Frontier Centers for funding based on their potential for transformational advances in the most promising research areas at the intellectual frontiers of physics. Caltech's IQIM was chosen for funding from more than 50 proposals this year. 

The NSF's decision to fund the IQIM leverages the groundwork done by the Center for Exotic Quantum Systems (CEQS), a program funded by the Gordon and Betty Moore Foundation, as well as an earlier NSF-sponsored Institute for Quantum Information (IQI). With the support of the NSF and the Moore Foundation, the new Physics Frontiers Center, CEQS, and IQI will be merged into a single entity—the Institute for Quantum Information and Matter.

"The unrestricted funds provided by the Moore Foundation had a dramatic effect on the decision to fund this Physics Frontiers Center," says Caltech president Jean-Lou Chameau. "That discretionary funding allowed the provost to provide seed money to what might otherwise have been considered a somewhat risky, unconventional field of study. Now, it is one of our most exciting and rapidly growing research initiatives."

Fundamental particles at the atomic level behave according to the laws of quantum physics, which in many respects defy common sense. At this level, individual particles of a composite system can become strongly correlated, or entangled, in such a way that they maintain their relation to one another no matter where they exist in the universe. Such quantum entanglement can endow a system with astonishing properties.

The IQIM will bring together Caltech's established theoretical programs and analytic tools for studying the quantum realm with emerging laboratory capabilities that will allow scientists to delve deeper into quantum entanglement and the unimagined behaviors it may yield. The research is aimed at making advances in basic physics, as well as helping to provide scientific foundations for designing materials with remarkable properties; additionally, this work may eventually help point the way to a quantum computer capable of solving problems that today's digital computers could never handle.

"My colleagues and I believe that an exciting frontier of 21st-century science is the exploration of the surprising phenomena that can arise in highly entangled quantum systems," says H. Jeff Kimble, the William L. Valentine Professor and professor of physics at Caltech, who will direct the IQIM. "The IQIM will provide a sustaining base for our efforts to discover new principles and phenomena at this entanglement frontier."

In addition to Kimble, the Institute for Quantum Information and Matter will be led by three codirectors: Jim Eisenstein, the current director of CEQS and the Frank J. Roshek Professor of Physics and Applied Physics; Oskar Painter, professor of applied physics and executive officer for applied physics and materials science; and John Preskill, the current director of the IQI and the Richard P. Feynman Professor of Theoretical Physics.

Studies of quantum entanglement and its applications are necessarily multidisciplinary in nature. Therefore, the 16 Caltech faculty members who will make up the core of the new center are drawn from such disciplines as physics, applied physics, and computer science. The newly renovated historic Norman Bridge Laboratory of Physics and the IQI's home base in the Annenberg Center for Information Science and Technology will serve as two central hubs for IQIM faculty on campus.

"When you bring innovative scientists and engineers together and provide them with the facilities and collaborative spaces they need, magic happens. The magic involves transforming the way we think about and impact our world," says Ares Rosakis, chair of the Division of Engineering and Applied Science (EAS) at Caltech. "I am delighted that an initial collaboration beginning in 2000 between the Division of Engineering and Applied Science (EAS) and the Division of Physics, Mathematics and Astronomy (PMA)—the Institute of Quantum Information (IQI)—planted the seeds for this new NSF institute at Caltech."

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Kimm Fesenmaier
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Caltech Named World's Top University in New Times Higher Education Global Ranking

PASADENA, Calif.—The California Institute of Technology (Caltech) has been rated the world's number one university in the 2011–2012 Times Higher Education global ranking of the top 200 universities, displacing Harvard University from the top spot for the first time in the survey's eight-year history.

Caltech was number two in the 2010–2011 ranking; Harvard and Stanford University share the second spot in the 2011–2012 survey, while the University of Oxford and Princeton University round out the top five.

"It's gratifying to be recognized for the work we do here and the impact it has—both on our students and on the global community," says Caltech president Jean-Lou Chameau. "Today's announcement reinforces Caltech's legacy of innovation, and our unwavering dedication to giving our extraordinary people the environment and resources with which to pursue their best ideas. It's also truly gratifying to see three California schools—including my alma mater, Stanford—in the top ten."

Thirteen performance indicators representing research (worth 30% of a school's overall ranking score), teaching (30%), citations (30%), international outlook (which includes the total numbers of international students and faculty and the ratio of scholarly papers with international collaborators; 7.5%), and industry income (a measure of innovation; 2.5%) are included in the data. Among the measures included are a reputation survey of 17,500 academics; institutional, industry, and faculty research income; and an analysis of 50 million scholarly papers to determine the average number of citations per scholarly paper, a measure of research impact.

"We know that innovation is the driver of the global economy, and is especially important during times of economic volatility," says Kent Kresa, chairman of the Caltech Board of Trustees. "I am pleased that Caltech is being recognized for its leadership and impact; this just confirms what many of us have known for a long time about this extraordinary place."

"Caltech has been one of California's best-kept secrets for a long time," says Caltech trustee Narendra Gupta. "But I think the secret is out!"

Times Higher Education, which compiled the listing using data supplied by Thomson Reuters, reports that this year's methodology was refined to ensure that universities with particular strength in the arts, humanities, and social sciences are placed on a more equal footing with those with a specialty in science subjects. Caltech—described in a Times Higher Education press release as "much younger, smaller, and specialised" than Harvard—was nevertheless ranked the highest based on their metrics.

According to Phil Baty, editor of the Times Higher Education World University Rankings, "the differences at the top of the university rankings are miniscule, but Caltech just pips Harvard with marginally better scores for 'research—volume, income, and reputation,' research influence, and the income it attracts from industry. With differentials so slight, a simple factor plays a decisive role in determining rank order: money."

"Harvard reported funding increases similar in proportion to other institutions, whereas Caltech reported a steep rise (16%) in research funding and an increase in total institutional income," Baty says.

Data for the Times Higher Education's World University Rankings was provided by Thomson Reuters from its Global Institutional Profiles Project (http://science.thomsonreuters.com/globalprofilesproject/), an ongoing, multistage process to collect and validate factual data about academic institutional performance across a variety of aspects and multiple disciplines.

For a full list of the world's top 200 schools and all of the performance indicators, go to http://www.timeshighereducation.co.uk/world-university-rankings/.

# # # 

The California Institute of Technology (Caltech) is a small, private university in Pasadena that conducts instruction and research in science and engineering, with a student body of about 900 undergraduates and 1,200 graduate students. Recognized for its outstanding faculty, including several Nobel laureates, and such renowned off-campus facilities as the Jet Propulsion Laboratory, the W. M. Keck Observatory, and the Palomar Observatory, Caltech is one of the world's preeminent research centers.

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Astronomers Discover a Black Hole Ripping a Star Apart

Astronomers have discovered a supermassive black hole tearing a star to shreds. In late March, NASA's Swift satellite detected flares of X rays and gamma rays from a mysterious source about 3.9 billion light years away. To follow up on the strange signal, astronomers used the 40-meter dish at Caltech's Owens Valley Radio Observatory (OVRO), the Combined Array for Research in Millimeter-wave Astronomy (CARMA)—of which Caltech is a member institution—and other telescopes that observe in centimeter, millimeter, and radio wavelengths. The subsequent data showed that the source is most likely a star being ripped apart by a black hole millions of times more massive than the sun.

"This is a remarkable discovery," says John Carpenter, a senior research associate in astronomy at Caltech and executive director of OVRO. "We are likely witnessing the birth of a jet as a stray star is ripped apart by a massive black hole." The astronomers describe their results in the August 25 issue of the journal Nature.

When the stellar shreds spiral in toward the black hole, which sits at the center of a galaxy, they heat up and produce powerful jets of particles that stream out at nearly the speed of light. Astronomers have predicted that these violent events could happen, and they've seen them before, but only as bright flares in optical, ultraviolet, and X-ray wavelengths.

"When I first saw the CARMA detection, I literally fell out of my chair," says Ashley Zauderer, an astronomer at the Harvard-Smithsonian Center for Astrophysics who led the team. The astronomers say that this is the first time such a scenario—called a tidal disruption event—has been observed at radio wavelengths, suggesting that scanning the skies for similar radio signals could be a fruitful way to find more stars being devoured by a black hole.

In addition to Carpenter, the Caltech researchers on the team are Shri Kulkarni, John D. and Catherine T. MacArthur Professor of Astronomy and Planetary Sciences; graduate students Kunal Mooley, Walter Max-Moerbeck, and Joseph Richards; Nikolaus Volgenau, CARMA assistant director of operations; Tony Readhead, Barbara and Stanley Rawn, Jr., Professor of Astronomy and director of OVRO; and staff scientist Martin Shepherd.

To read more and to watch an animated video, click here.

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Marcus Woo
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New LIGO Executive Director Named

PASADENA, Calif.—David Reitze has been named executive director of the Laser Interferometer Gravitational-Wave Observatory (LIGO), designed and operated by the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT), with funding from the National Science Foundation (NSF). Reitze has also been named a senior research associate at Caltech.

A professor of physics at the University of Florida, Gainesville, and a visiting associate at Caltech since 2007, Reitze will succeed the retiring Jay Marx. Marx, a senior research associate in physics at Caltech, served as executive director since 2006 and will continue to work on LIGO part-time.

"I'm really excited about joining the LIGO laboratory and Caltech and serving in the role of executive director," says Reitze, who received his PhD from the University of Texas at Austin in 1990 and has been involved in the LIGO project since 1996. His early research focused on ultrafast optics and the development of high-power optical components and ultrafast lasers. More recently, he led the design effort for the input optics of Advanced LIGO, a more sensitive incarnation of the detector slated to begin operation in 2014. "In addition to the incredible science that LIGO will do, one of the main reasons I accepted the position was the outstanding quality and commitment of the LIGO laboratory staff," he says.

LIGO was originally proposed decades ago as a means of detecting gravitational waves. Gravitational waves are ripples in the fabric of space and time—produced by massive accelerating objects such as black-hole and neutron-star collisions—which propagate outward through the universe. They were first predicted in 1916 as a consequence of Albert Einstein's general theory of relativity.

Each of the L-shaped LIGO interferometers (including 4-km detectors in Hanford, Washington, and Livingston, Louisiana) use a laser split into two beams that travel back and forth down long arms (which are beam tubes from which the air has been evacuated). The beams are used to monitor the distance between precisely configured mirrors. According to Einstein's theory, the relative distance between the mirrors will change very slightly when a gravitational wave passes by. 

LIGO research is carried out by the LIGO Scientific Collaboration (LSC), a group of 840 scientists at universities around the United States and in 13 other countries; Reitze served as the LSC spokesperson from 2007 to 2011.

The LSC network includes the LIGO interferometers and the GEO600 interferometer, a project located near Hannover, Germany, and designed and operated by scientists from the Max Planck Institute for Gravitational Physics, along with partners in the United Kingdom funded by the Science and Technology Facilities Council (STFC). The LSC works jointly with the Virgo Collaboration—which designed and constructed the 3-km long Virgo interferometer located in Cascina, Italy—to analyze data from the LIGO, GEO, and Virgo interferometers.

The next major milestone for LIGO is Advanced LIGO, which will incorporate upgraded designs and technologies that have been developed by the LSC. The original configuration of LIGO was sensitive enough to detect a change in the lengths of the 4-km arms by a distance one-thousandth the size of a proton; Advanced LIGO, which will utilize the infrastructure of LIGO, will be 10 times more sensitive.

The increased sensitivity will be important because it will allow scientists to detect cataclysmic events such as black-hole and neutron-star collisions at 10-times-greater distances. And because LIGO can "see" in all directions, Advanced LIGO will be 1,000 times more likely to detect gravitational waves and will make important contributions to astronomy and physics.

"This is a great time in LIGO's history," Reitze says. "Over the past decade, we've demonstrated that we can build and operate the LIGO interferometers with truly exquisite sensitivity and use them to conduct scientifically interesting searches for gravitational waves. It's also an exciting time for worldwide gravitational-wave scientific community," he adds.

"We're really delighted to have Dr. Reitze take over the leadership of LIGO. He knows the project, the science, and the challenges, and is superbly qualified to lead the team in bringing the Advanced LIGO detector on line," says Tom Soifer, professor of physics, director of the Spitzer Science Center, and chair of the Division of Physics, Mathematics and Astronomy at Caltech. "Jay Marx set a high standard," he adds, "and Dave is fully ready to match that in leading LIGO in this most exciting time. We're looking forward to the first detections of gravitational waves from astronomical sources, and the new window on the universe it will provide."

"Once Advanced LIGO is running, we'll continue to work closely with our European colleagues at GEO600 and Virgo as part of the new and growing global gravitational-wave network," Reitze says. "The Large Cryogenic Gravitational Wave Telescope in Japan is scheduled to begin operation soon after Advanced LIGO, adding a fourth detector to the network. The global network will allow us to look at the underlying sources of gravitational waves in tandem with other types of astronomical telescopes—optical, radio, X-ray, gamma ray—to give a much better picture of the astrophysics of the most violent events in the universe."

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Caltech Researcher Granted Precious Observation Time at NASA's Hubble Space Telescope

For many astronomers, NASA's Hubble Space Telescope (HST) is considered the crème de la crème of research tools—one of the best observatories available for their studies. This being the case, competition for time with the telescope can be fierce.

But Heather A. Knutson, a recent addition to the Division of Geological and Planetary Sciences at Caltech, will soon get the chance to spend some quality time with the telescope. She is part of an international research team, lead by scientists at the University of Exeter in the UK, which has secured nearly 200 hours of observation time on HST. Knutson will study the atmospheres of two exoplanets—planets outside of our solar system—over 15 orbits, which roughly translates to 23 hours of observation time.

"We have very little idea of what to expect, as these planets are very different than anything we have in our own solar system," says Knutson, assistant professor of planetary science. "The really exciting thing about this project is that it is an opportunity to study a large sample of planets. Most of the time, we get to look at one, maybe two things at a time, so you don't really get the context of whether or not what you are looking at is typical of the planets that you study, or if it's an oddball."

A full press release on the project can be read here.

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Neutrino Experiment Starts Taking Data

A new experiment that will answer fundamental questions about neutrinos, aiming to solve some of the biggest mysteries about the universe—why there's so much more matter than antimatter, for example—is now open for business. About two weeks ago, the Daya Bay Reactor Neutrino Experiment, lying underground in the mountains of southern China near Hong Kong, began taking data with its first set of twin detectors.

The start of the experiment is a culmination of six years of planning and construction, involving more than 200 scientists from around the world. "It's taken some time, but it's all coming together quite well," says Bob McKeown, professor of physics and the leader of the Caltech team involved in the project. "The detectors are performing extremely well. Everyone's very excited."

Neutrinos are uncharged particles, created in nuclear reactions such as those in the sun and in nuclear-power plants. Neutrinos zip through space at near the speed of light, hardly interacting with anything. In fact, billions of neutrinos are streaming through your body at this very second. About a dozen years ago, physicists discovered that neutrinos changed from one type, or "flavor," to another. Previously, physicists thought neutrinos are massless, but these transformations, called oscillations, mean that they actually do have a tiny amount of mass—they're about a million times less massive than an electron.

There are three flavors of neutrinos—muon, electron, and tau—and the way they transform into one another depends on three parameters called mixing angles. The Daya Neutrino Experiment will make the most precise measurement yet of the mixing angle called θ13, which describes how the electron neutrino transforms into the tau neutrino. The experiment will measure the electron antineutrinos—the antimatter counterpart of a neutrino—that are produced by the nuclear reactors in the nearby China Guangdong Nuclear Power Group.

Only two detectors are completed, but within the next year, McKeown says, the remaining six will be finished. Each detector is a 100-ton transparent cylinder filled with liquid, which will flash when antineutrinos strike and interact. Sitting below hundreds of feet of rock, the detectors are shielded from cosmic rays, which are a primary source of background noise. The detectors are also submerged in water in order to block out the radioactivity from the rock walls. Two miles of underground tunnels connect the detectors.

The Caltech team was in charge of designing and building the 24 calibration devices (three for each detector) that enable physicists to understand what the detectors will observe.

"Caltech has quite an important history working in this field," McKeown says. Nobel laureate Willy Fowler did some of the first calculations of solar neutrinos in the 1950s. In the 1980s, Felix Boehm studied antineutrinos produced in nuclear reactors. McKeown started his own research group after Boehm retired, working on the KamLAND experiment in Japan, which was one of the first experiments to conclusively observe neutrino oscillations. 

Read more about the startup of the Daya Bay Reactor Neutrino Experiment here. Click through a slideshow of the facility here.

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Marcus Woo
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Caltech Astronomer Nominated to National Science Board

President Barack Obama has nominated Anneila Sargent, vice president for student affairs and the Rosen Professor of Astronomy, to the National Science Board, the governing body of the National Science Foundation.

As an astronomer, Sargent studies disks of gas and dust that form stars and planets. She first arrived at Caltech more than 40 years ago as a graduate student. Since then, she has worked as a research fellow, a member of the professional staff, a senior research fellow, and a senior research associate, becoming a professor in 1998. Sargent has served as the director of the Owens Valley Radio Observatory and the Combined Array for Research in Millimeter-Wave Astronomy. She has also been president of the American Astronomical Society, chair of NASA's Space Science Advisory Committee, and chair of the National Research Council's Board of Physics and Astronomy. A former member of the National Science Foundation's Mathematical and Physical Sciences Advisory Committee, she is a fellow of the American Academy of Arts and Sciences.

The National Science Board consists of 25 members who serve six-year appointments. Eight members are nominated every two years and must be confirmed by the Senate. Previous members from Caltech include Barry Barish, the Linde Professor of Physics, Emeritus; the late Lee DuBridge, physicist, former Caltech president, and science advisor to Presidents Harry Truman and Richard Nixon; and the late William Fowler, astrophysicist and Nobel laureate.

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Caltech-Led Astronomers Discover the Largest and Most Distant Reservoir of Water Yet

PASADENA, Calif.—Water really is everywhere. Two teams of astronomers, each led by scientists at the California Institute of Technology (Caltech), have discovered the largest and farthest reservoir of water ever detected in the universe. Looking from a distance of 30 billion trillion miles away into a quasar—one of the brightest and most violent objects in the cosmos—the researchers have found a mass of water vapor that's at least 140 trillion times that of all the water in the world's oceans combined, and 100,000 times more massive than the sun.

Because the quasar is so far away, its light has taken 12 billion years to reach Earth. The observations therefore reveal a time when the universe was just 1.6 billion years old. "The environment around this quasar is unique in that it's producing this huge mass of water," says Matt Bradford, a scientist at NASA's Jet Propulsion Laboratory (JPL), and a visiting associate at Caltech. "It's another demonstration that water is pervasive throughout the universe, even at the very earliest times." Bradford leads one of two international teams of astronomers that have described their quasar findings in separate papers that have been accepted for publication in the Astrophysical Journal Letters.

A quasar is powered by an enormous black hole that is steadily consuming a surrounding disk of gas and dust; as it eats, the quasar spews out huge amounts of energy. Both groups of astronomers studied a particular quasar called APM 08279+5255, which harbors a black hole 20 billion times more massive than the sun and produces as much energy as a thousand trillion suns.

Since astronomers expected water vapor to be present even in the early universe, the discovery of water is not itself a surprise, Bradford says. There's water vapor in the Milky Way, although the total amount is 4,000 times less massive than in the quasar, as most of the Milky Way’s water is frozen in the form of ice.

Nevertheless, water vapor is an important trace gas that reveals the nature of the quasar. In this particular quasar, the water vapor is distributed around the black hole in a gaseous region spanning hundreds of light-years (a light-year is about six trillion miles), and its presence indicates that the gas is unusually warm and dense by astronomical standards. Although the gas is a chilly –53 degrees Celsius (–63 degrees Fahrenheit) and is 300 trillion times less dense than Earth's atmosphere, it's still five times hotter and 10 to 100 times denser than what's typical in galaxies like the Milky Way.

The water vapor is just one of many kinds of gas that surround the quasar, and its presence indicates that the quasar is bathing the gas in both X-rays and infrared radiation. The interaction between the radiation and water vapor reveals properties of the gas and how the quasar influences it. For example, analyzing the water vapor shows how the radiation heats the rest of the gas. Furthermore, measurements of the water vapor and of other molecules, such as carbon monoxide, suggest that there is enough gas to feed the black hole until it grows to about six times its size. Whether this will happen is not clear, the astronomers say, since some of the gas may end up condensing into stars or may be ejected from the quasar.

Bradford's team made their observations starting in 2008, using an instrument called Z-Spec at the Caltech Submillimeter Observatory (CSO), a 10-meter telescope near the summit of Mauna Kea in Hawaii. Z-Spec is an extremely sensitive spectrograph, requiring temperatures cooled to within 0.06 degrees Celsius above absolute zero. The instrument measures light in a region of the electromagnetic spectrum called the millimeter band, which lies between infrared and microwave wavelengths. The researchers' discovery of water was possible only because Z-Spec’s spectral coverage is 10 times larger than that of previous spectrometers operating at these wavelengths. The astronomers made follow-up observations with the Combined Array for Research in Millimeter-Wave Astronomy (CARMA), an array of radio dishes in the Inyo Mountains of Southern California.

This discovery highlights the benefits of observing in the millimeter and submillimeter wavelengths, the astronomers say. The field has developed rapidly over the last two to three decades, and to reach the full potential of this line of research, the astronomers—including the study authors—are now designing CCAT, a 25-meter telescope to be built in the Atacama Desert in Chile. CCAT will allow astronomers to discover some of the earliest galaxies in the universe. By measuring the presence of water and other important trace gases, astronomers can study the composition of these primordial galaxies.

The second group, led by Dariusz Lis, senior research associate in physics at Caltech and deputy director of the CSO, used the Plateau de Bure Interferometer in the French Alps to find water. In 2010, Lis's team was looking for traces of hydrogen fluoride in the spectrum of APM 08279+5255, but serendipitously detected a signal in the quasar's spectrum that indicated the presence of water. The signal was at a frequency corresponding to radiation that is emitted when water transitions from a higher energy state to a lower one. While Lis's team found just one signal at a single frequency, the wide bandwidth of Z-Spec enabled Bradford and his colleagues to discover water emission at many frequencies. These multiple water transitions allowed Bradford's team to determine the physical characteristics of the quasar's gas and the water's mass.

The other authors on Lis's paper, "Discovery of water vapor in the high-redshift quasar APM 08279+5255 at Z=3.91," are Tom Phillips, Caltech's John D. MacArthur Professor of Physics and director of the CSO; David Neufeld of Johns Hopkins University; Maryvonne Gerin of the Paris Observatory and the French National Center for Scientific Research; and Roberto Neri of the Institute of Millimeter Radio Astronomy in France. Funding was provided by the National Science Foundation (NSF).

The authors on Bradford's paper, "The water vapor spectrum of APM 08279+5255: X-ray heating and infrared pumping over hundreds of parsecs," include Caltech's Hien Nguyen, a visiting associate and lecturer in physics; Jamie Bock, senior faculty associate in physics and scientist at JPL; and Jonas Zmuidzinas, the Merle Kingsley Professor of Physics and chief technologist at JPL. The other authors are Alberto Bolatto of the University of Maryland, College Park; Philip Maloney, Jason Glenn, and Julia Kamenetzky of the University of Colorado, Boulder; James Aguirre, Roxana Lupu, and Kimberly Scott of the University of Pennsylvania; Hideo Matsuhara of the Institute of Space and Astronautical Science in Japan; Eric Murphy of the Carnegie Institution for Science; and Bret Naylor of JPL.

Funding for Z-Spec was provided by the NSF, NASA, the Research Corporation, and partner institutions. The CSO is operated by Caltech under contract from the NSF. CARMA was built and is operated by Caltech, UC Berkeley, the University of Maryland, College Park, the University of Illinois at Urbana-Champaign, and the University of Chicago. CARMA is funded by a combination of state and private sources, as well as the NSF and its University Radio Observatories program.

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Marcus Woo
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Bring In the (Nano) Noise

At the forefront of nanotechnology, researchers design miniature machines to do big jobs, from treating diseases to harnessing sunlight for energy. But as they push the limits of this technology, devices are becoming so small and sensitive that the behavior of individual atoms starts to get in the way. Now Caltech researchers have, for the first time, measured and characterized these atomic fluctuations—which cause statistical noise—in a nanoscale device.

Physicist Michael Roukes and his colleagues specialize in building devices called nanoelectromechanical systems—NEMS for short—which have a myriad of applications. For example, by detecting the presence of proteins that are markers of disease, the devices can serve as cheap and portable diagnostic tools—useful for keeping people healthy in poor and rural parts of the world. Similar gadgets can measure toxic gases in an enclosed room, providing a warning for the inhabitants.

Two years ago, Roukes's group created the world's first nanomechanical mass spectrometer, enabling the researchers to measure the mass of a single biological molecule. The device, a resonator that resembles a tiny bridge, consists of a thin strip of material 2 microns long and 100 nanometers wide that vibrates at a resonant frequency of several hundred megahertz. When an atom is placed on the bridge, the frequency shifts in proportion to the atom's mass. 

But with increasingly sensitive devices, the random motions of the atoms come into play, generating statistical noise. "It's like fog or smoke that obscures what you're trying to measure," says Roukes, who's a professor of physics, applied physics, and bioengineering. In order to distinguish signal from noise, researchers have to understand what's causing the ruckus.

So Roukes—along with former graduate student and staff scientist Philip X. L. Feng, former graduate student Ya-Tang (Jack) Yang, and former postdoc Carlo Callegari—set out to measure this noise in a NEMS resonator. They described their results in the April issue of the journal Nano Letters.

In their experiment, the researchers sprayed xenon gas onto a bridgelike resonator that's similar to the one they used to weigh biological molecules. The xenon can accumulate in a one-atom-thick layer on the surface, like marbles covering a table. In such an arrangement—a so-called monolayer—the atoms are packed so tightly together that they don't have much room to move. But to study noise, the researchers created a submonolayer, which doesn't have enough atoms to completely cover the surface of the resonator. Because of the extra space, the atoms have more freedom to move around, which generates more noise in the system.

The atoms in the submonolayer do one of three things: they stick to the surface, become unstuck and fly off, or slide off. Or in physics speak, the atoms adsorb, desorb, or diffuse. Previous theories had predicted that the noise is most likely due to atoms sticking and unsticking. But now that the researchers were able to observe what actually happens in such a device, they discovered that diffusion dominates the noise. What's noteworthy, the researchers say, is that they found that when an atom slides along the surface of the resonator, it causes the device's vibrating frequency to fluctuate. This is the first time anyone has measured this effect, since previous devices were not sensitive to this sort of diffusion. They also found new power laws in the spectra of noise frequencies—quantitative descriptions of the frequencies at which the atoms vibrate.

There's still a lot more to learn about the physics of this noise, the researchers say. Ultimately, they will need to figure out how to get rid of it or suppress it to build better NEMS devices. But understanding this noise—by measuring the random movement of individual atoms—is itself fascinating science, Roukes says. "It's a new window into how things work in the nanoscale world."

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Marcus Woo
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Stone Awarded Goddard Astronautics Award

Ed Stone, the David Morrisroe Professor of Physics at Caltech and lead scientist on the Voyager 1 and Voyager deep-space probe missions since 1972, was awarded the Goddard Astronautics Award from the American Institute of Aeronautics and Astronautics (AIAA) at a gala ceremony on May 11 in Washington D.C.

The Goddard Award, which honors rocketry pioneer Robert H. Goddard, is the highest honor bestowed by the AIAA; previous winners include Theodore von Karman, James van Allen, Werner von Braun, and Charles Elachi.

Stone joined Caltech's faculty as a research fellow in 1964, the same year he received his PhD from the University of Chicago, and achieved the rank of full professor in 1976. A principal investigator on nine NASA spacecraft missions and coinvestigator on five others, he was formerly director of the Jet Propulsion Laboratory.

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Kathy Svitil
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