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Sankar Das Sarma and Ian Spielman Named 2018 Highly Cited Researchers

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Category: Department News
Published: Wednesday, December 05 2018 11:53

Sankar Das Sarma and Ian Spielman join six other faculty members in the University of Maryland’s College of Computer, Mathematical, and Natural Sciences included on Clarivate Analytics’ 2018 list of Highly Cited Researchers, a compilation of influential names in science.

Sankar Das Sarma is a Richard E. Prange Chair and Distinguished University Professor in Physics, Joint Quantum Institute Fellow, and Condensed Matter Theory Center Director. Das Sarma was included in all previous compilations of this list in 2017, 2016, 2015, 2014 and 2001.

Ian Spielman is an Adjunct Professor of Physics, JQI Fellow and National Institute of Standards and Technology (NIST) Fellow. Spielman was also included in the 2017 compilation.

Four New Gravitational Wave Events Detected from Black Hole Mergers

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Category: Research News
Published: Monday, December 03 2018 12:20

GWTC 1 masses.croppedThe Virgo Collaboration and the LIGO Scientific Collaboration, which includes UMD Physics Professors Peter Shawhan and Alessandra Buonanno, announced the detection of four new gravitational wave events from black hole mergers. (Image: LIGO-Virgo/Frank Elavsky/Northwestern) 

 University of Maryland physicists contribute to identification of events that now total 10 black hole mergers and one neutron star merger

Scientists announced four new observations of gravitational waves—ripples in the fabric of spacetime—from the final moments of black hole mergers.

The twin Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors—located in Livingston, Louisiana, and Hanford, Washington—and the Virgo detector located near Pisa, Italy detected the gravitational wave events. The Virgo Collaboration and the LIGO Scientific Collaboration (LSC) announced the discoveries on December 1, 2018, at the Joint Space-Science Institute’s  Gravitational Wave Physics and Astronomy Workshop hosted by the University of Maryland in College Park, Maryland. Two scientific papers describing these new findings have been initially published on the arXiv repository of electronic preprints and include a catalog of all gravitational wave detections and candidate events observed to date.

“These results mark an evolution in the way we are thinking about binary black hole mergers detected by LIGO and Virgo,” said Peter Shawhan, a UMD professor of physics and an LSC principal investigator who serves as the LSC’s data analysis committee chair. “While we carefully determine the properties of the individual events, such as the masses and spins of the black holes, we are also looking at the big picture: the distribution of these properties and what that can tell us about how massive stars live and die.”

Gravitational waves carry information about their origins and about the nature of gravity that cannot otherwise be obtained. During a two-year span, physicists on the LIGO and Virgo teams detected gravitational waves from 10 black hole mergers and one merger of neutron stars, which are the dense, spherical remains of stellar explosions. The four new observations—named GW170729, GW170809, GW170818 and GW170823 for the dates they were detected—include some record breakers.

One of the new events, GW170729, is the most massive and distant gravitational wave source ever observed. This black hole merger, which happened roughly 5 billion years ago, transformed an equivalent energy of almost five solar masses into gravitational energy.

Another new event, GW170818, was triangulated well in the sky by the LIGO and Virgo detectors, making it the second-best localized gravitational wave source after the neutron star merger. The position of the binary black holes, located 2.5 billion light-years from Earth, was identified in the sky with a precision of 39 square degrees.

A major contributor to this accomplishment was Alessandra Buonanno—a UMD College Park Professor of Physics and LSC principal investigator who also has an appointment as director at the Max Planck Institute for Gravitational Physics in Potsdam, Germany. Buonanno has led the effort to develop highly accurate models of gravitational waves that black holes generate in the final process of orbiting and colliding with each other. The scientists use these waveform models to localize the source in the sky and identify it as a pair of orbiting black holes.

“State-of-the-art waveform models, advanced data processing and better calibration of the instruments have allowed us to infer astrophysical parameters of previously announced events more accurately and discover four new gravitational wave transients from black hole mergers,” Buonanno said. “I look forward to the next observing run in spring 2019, where we expect to detect more than two black hole mergers per month of collected data.” 

The scientific papers describing the new findings include a catalog of all gravitational wave detections and candidate events observed from September 12, 2015 to August 25, 2017.

Scientists observed GW170817—the merger of two neutron stars—in both gravitational waves and light. Shawhan and his students at UMD worked with other LIGO and Virgo team members to establish a program to quickly share information about each gravitational wave event candidate, including sky location, with astronomers. This enabled astronomers to look for the event with their telescopes and other instruments, marking an exciting new chapter in multi-messenger astronomy, a field in which cosmic objects are observed simultaneously in different forms of radiation.

“The one neutron star merger in the catalog, GW170817, may look a bit lonely, but we have learned so many things about it by looking at the gravitational wave data together with the incredibly rich range of follow-up observations,” said Shawhan, who is also a fellow of the Joint Space-Science Institute. “Still, we have a lot of unanswered questions about the population of binary neutron stars that future data should fill in for us.”

In one of the two new papers, the scientists carefully investigate the characteristics of the merging black hole population. Most notably, the researchers found that almost all black holes formed from stars are lighter than 45 times the mass of the sun.

“The LIGO and Virgo collaborations have worked hard to release the event properties and also the data in which these signals were found so that other scientists can analyze them with their own tools and compare them with theories of stellar evolution and gravitational wave emission,” Shawhan added.

The first detection of gravitational waves, observed on September 14, 2015, was a milestone in physics and astronomy. It confirmed a major prediction of Albert Einstein’s 1915 general theory of relativity and marked the beginning of the new field of gravitational wave astronomy.

###

This press release was adapted from text provided by the LIGO and Virgo Collaborations.

The research paper, “GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs,” by the LIGO Scientific Collaboration and the Virgo Collaboration, was presented December 1, 2018 at the Joint Space-Science Institute–Gravitational Wave Physics and Astronomy Workshop and is available on the arXiv.

The research paper, “Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo,” by the LIGO Scientific Collaboration and the Virgo Collaboration, was presented December 1, 2018 at the Joint Space-Science Institute–Gravitational Wave Physics and Astronomy Workshop and is available on the arXiv.

Media Relations Contact: Abby Robinson, 301-405-5845, This email address is being protected from spambots. You need JavaScript enabled to view it.

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About LIGO and Virgo
LIGO is funded by the National Science Foundation (NSF) and operated by Caltech and MIT, which conceived of LIGO and led the Initial and Advanced LIGO projects. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council-OzGrav) making significant commitments and contributions to the project. More than 1,200 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. A list of additional partners is available at https://my.ligo.org/census.php.

The Virgo collaboration consists of more than 300 physicists and engineers belonging to 28 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; 11 from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in the Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with IFAE and the Universities of Valencia and Barcelona; two in Belgium with the Universities of Liege and Louvain; Jena University in Germany; and the European Gravitational Observatory (EGO), the laboratory hosting the Virgo detector near Pisa in Italy, funded by CNRS, INFN, and Nikhef. A list of the Virgo Collaboration can be found at http://public.virgo-gw.eu/the-virgo-collaboration/. More information is available on the Virgo website at www.virgo-gw.eu.

About the College of Computer, Mathematical, and Natural Sciences
The College of Computer, Mathematical, and Natural Sciences at the University of Maryland educates more than 9,000 future scientific leaders in its undergraduate and graduate programs each year. The college's 10 departments and more than a dozen interdisciplinary research centers foster scientific discovery with annual sponsored research funding exceeding $175 million.

 
 
 

Sundrum Win APS Sakurai Prize

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Category: Department News
Published: Tuesday, November 06 2018 09:56

Sundrum 2018 levineRaman Sundrum. Photo: Faye Levine

The American Physical Society awarded its 2019 J.J. Sakurai Prize for Theoretical Particle Physics to Raman Sundrum, a Distinguished University Professor of Physics at the University of Maryland. Sundrum’s collaborator on two key papers, Harvard University Physics Professor Lisa Randall, also received the award. 

Sundrum and Randall were honored for making a number of theoretical predictions that set off a wave of experiments searching for theoretical subatomic particles—experiments that are still active today, almost two decades later.

“As a theoretical physicist, I always hope my ideas are ultimately connected to experiments that examine the nature of reality,” said Sundrum, who also holds the John S. Toll Chair in Physics and directs the Maryland Center for Fundamental Physics. “It’s very meaningful to me that this prize was awarded for motivating experimental searches for new particles.”

Sundrum studies theoretical particle physics, which seeks to understand the subatomic particles that make up the world around us. The laws of physics—the laws of quantum mechanics, in particular—strongly suggest that such particles should be far heavier than physicists have observed them to be. This disparity is nicknamed the “hierarchy puzzle.”

In 1999, Sundrum and Randall published two papers in the journal Physical Review Letters that have been cited nearly 20,000 times in all. Their work proposed an extra dimension of space that is capable of distorting, or warping, space and time as a solution to the puzzle. People do not experience this dimension because unlike the three dimensions of space, which go on forever, this dimension is highly limited: it is more like an extradimensional, subatomic “bubble.” 

However, this dimension can affect particles. In particular, it can dramatically change the mass of particles, making the “true” mass of the particle match the mass predicted by quantum mechanics.

Sundrum and Randall’s work, which became known as the Randall-Sundrum models, makes a number of other predictions. In particular, it predicts the existence of new types of gravitons, which are theoretical particles that carry the force of gravity. This prediction inspired experiments to look for gravitons using the Large Hadron Collider (LHC), the world’s largest particle accelerator located at CERN near Geneva, Switzerland.

“These gravitons would be microscopic gravitational waves bouncing around the extra dimension, so you need a big magnifying glass, which is what the LHC is,” Sundrum said. “Our work has also inspired experiments to search for all kinds of other particles that might exist in the extra dimension. It continues to be an active area of study.”

Sundrum learned about theoretical particle physics as an undergraduate student at the University of Sydney in Australia.

“One day, I came upon a Scientific American article about particle physics,” Sundrum said. “I didn’t even know there was such a thing until I saw that article, but I found the subject so interesting that I decided to study it.”

After receiving his B.S. in mathematics and physics from the University of Sydney in 1984, Sundrum studied elementary particle theory at Yale University, where he received his Ph.D. in 1990. He then took several postdoctoral positions, including one at Boston University from 1996 to 1999. 

At Boston University, he studied “dark energy,” a theoretical form of energy that permeates the universe. Sundrum published a number of papers that tackled the topic using extra dimensions. These papers caught the attention of Randall, who invited Sundrum to collaborate. While they did not solve the mysteries of dark energy, their results turned out to be applicable to the hierarchy problem. 

“Our finding was completely unexpected,” Sundrum said. “I threw myself at the problem of dark energy and failed, but my failure spun off into a solution for the hierarchy problem.”

After taking a faculty position at the Johns Hopkins University, Sundrum came to UMD in 2010, where he continues to study particle physics in extra dimensions and other topics. Today, he is especially interested in warped extra dimensions as a source of macroscopic gravitational waves—such as those detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO).

In 2018, Sundrum and three colleagues from the Maryland Center for Fundamental Physics—Michael Geller, Anson Hook and Yuhsin Tsai—wrote a paper that is accepted for publication in the journal Physical Review Letters proposing to study the gravitational wave background. Unlike gravitational wave signals from black hole or neutron star mergers, signals from the gravitational wave background can originate from collisions between extradimensional bubbles in the very early universe. These extradimensional bubbles are related to the “bubbles” that make it possible to theoretically solve the hierarchy problem and can potentially teach scientists about the early universe. 

“Our study showed that gravitational wave background signals should not be evenly spread across the entire universe, but would rather have hot spots and cold spots,” Sundrum said. “Importantly, the pattern of the hot spots could tell us about how the universe was operating at the very beginning, possibly even before the Big Bang.” 

###

The paper, “Primordial Anisotropies in the Gravitational Wave Background from Cosmological Phase Transitions,” Michael Geller, Anson Hook, Raman Sundrum and Yuhsin Tsai, is forthcoming in the journal Physical Review Letters.

The paper, “An Alternative to Compactification,” Lisa Randall and Raman Sundrum, was published in the journal Physical Review Letters on December 6, 1999.

The paper, “Large Mass Hierarchy from a Small Extra Dimension,” Lisa Randall and Raman Sundrum, was published in the journal Physical Review Letters on October 25, 1999.

Media Relations Contact: Irene Ying, 301-405-5204, This email address is being protected from spambots. You need JavaScript enabled to view it.

For a full listing of 2019 APS Award Recipients visit: http://www.aps.org/programs/honors/new-recipients.cfm

 

 

 

 

Jarzynski Wins APS Onsager Prize

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Category: Department News
Published: Tuesday, November 06 2018 05:56

jarzynski by levine 23Christopher Jarzynski. Photo: Faye Levine The American Physical Society awarded its 2019 Lars Onsager Prize in Theoretical Statistical Physics, to Chris Jarzynski,  a Distinguished University Professor in the University of Maryland’s Department of Chemistry and Biochemistry, Department of Physics, and Institute for Physical Science and Technology (IPST). Jarzynski will receive the prize, which recognizes outstanding research in theoretical statistical physics, at the society’s March Meeting 2019 in Boston.

“This particular award is very special to me because it’s named after Onsager, who was a real giant in theoretical statistical physics and is viewed as a founder of nonequilibrium statistical physics—the field that I work in,” Jarzynski said.

The award also demonstrates UMD’s strength in statistical physics, as the first Lars Onsager Prize was awarded in 1995 to Michael Fisher, a Distinguished University Professor Emeritus in IPST.

Statistical physicists use the tools of mathematics and statistics to investigate how atoms and molecules physically behave at extremely small scales, such as in quantum systems. More specifically, Jarzynski analyzes artificial molecular machines, develops efficient ways to compute the thermodynamic properties of complex systems and applies statistical physics to problems in biophysics.

“Because my work lies on the border of chemistry and physics, it’s been really helpful for me to be at an institute where there are other people with interdisciplinary interests,” said Jarzynski, who is also director of IPST. “IPST brings together really wonderful colleagues who are generous with their time and effort.”

In May 2018, Jarzynski co-authored a study published in the journal Nature Physics that devised and demonstrated a new way to measure “free energy”—the energy available to any system to perform useful work—in extremely small systems. By using microscopy to track and analyze the fluctuating motion or configuration of single molecules or other small objects, the new method can be applied to a greater variety of systems than previous techniques.

Going forward, Jarzynski plans to conduct research at the intersection of statistical mechanics—using probability and statistics to model the behavior of particles—and quantum physics. He will examine the fundamental constraints that the laws of thermodynamics place on information processing in quantum systems as well as investigate how to control and manipulate quantum systems.

Of the nearly 100 papers that Jarzynski has published, the most cited is a 1997 paper published in the journal Physical Review Letters. In this paper, Jarzynski described a method of expressing the second law of thermodynamics—which states that the level of disorder in the universe can only increase—for systems at the molecular scale.

“That was my very first paper in statistical physics,” said Jarzynski, who wrote and submitted the sole-author paper while a research associate at the Institute for Nuclear Theory based at the University of Washington. “After I published that result, I came up with further questions and I’ve stayed in that field for the last 20 years.”

The paper proved influential for the field of statistical physics: thousands of papers cite it and an equation in the paper became known as the Jarzynski equality.

“At first, there was some question of whether my paper was just a theoretical prediction,” Jarzynski said. “But a few years later, experiments started verifying my work.”

Then, when the 2018 Nobel Prize in physics was awarded for inventions in laser physics, the Nobel Committee for Physics specifically cited testing the Jarzynski equality as an application of one of the winning inventions—optical tweezers. Optical tweezers use laser beams to manipulate extremely small objects such as biological molecules.

The equality has now been verified in many systems, including quantum mechanical systems. In 2014, scientists helped verify the Jarzynski equality with a trapped ion system and published the results in the journal Nature Physics. The study’s authors included two former UMD postdocs—Kihwan Kim, an associate professor in the Institute for Interdisciplinary Information Sciences at Tsinghua University in Beijing, and Haitao Quan, an assistant professor of physics at Beijing’s Peking University.

The opportunity to recruit postdocs like Quan and promising graduate students to his lab was a key reason that Jarzynski moved to UMD in 2006 from the Los Alamos National Laboratory, where he worked for the preceding decade.

“The thing I’m most proud of here at Maryland is having built my own research group,” Jarzynski said. “I’ve been very fortunate in having terrific students and postdocs, many of whom are now in academic positions.”

One of those students will also be honored at the March Meeting alongside Jarzynski. Jordan Horowitz (Ph.D. ’10, physics), who is now a postdoctoral fellow in physics at the Massachusetts Institute of Technology and will soon start a position as an assistant professor at the University of Michigan, will receive the Irwin Oppenheim Award, which recognizes outstanding contributions to physics by early career scientists who publish in the journal Physical Review E.

###

The paper, “Equilibrium free energies from non-equilibrium trajectories with relaxation fluctuation spectroscopy,” David Ross, Elizabeth Strychalski, Christopher Jarzynski and Samuel Stavis, was published in the journal Nature Physics on May 28, 2018.

The paper, “Experimental test of the quantum Jarzynski equality with a trapped-ion system,” Shuoming An, Jing-Ning Zhang, Mark Um, Dingshun Lv, Yao Lu, Junhua Zhang, Zhang-Qi Yin, Haitao Quan and Kihwan Kim, was published in the journal Nature Physics on December 22, 2014.

The paper, “Nonequilibrium equality for free energy differences,” Christopher Jarzynski, was published in the journal Physical Review Letters on April 7, 1997.

Media Relations Contact: Irene Ying, 301-405-5204, This email address is being protected from spambots. You need JavaScript enabled to view it.

For a full listing of 2019 APS Award Recipients visit: http://www.aps.org/programs/honors/new-recipients.cfm

 

 

 

 

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