Eric Sembrat's Test Bonanza

When NASA launches a new telescope this Wednesday that will look at black holes in ways never seen before, Georgia Tech astrophysicist David Ballantyne will be more than a curious bystander. He helped plan the mission.

Ballantyne, one of the Institute’s black hole experts, is on the science team of NASA's Nuclear Spectroscopic Telescope Array (NuSTAR), which is scheduled for launch Wednesday morning. He’s one of a handful of people who decided where the high-energy X-ray telescope will point while in orbit. NuSTAR’s technology will allow it to image areas of the universe in never-before-seen ways. Ballantyne will be among the first scientists to see the images and examine the data when it becomes available this later this summer.  

“NuSTAR will provide a window to the murky world of black holes,” said Ballantyne, an assistant professor in the School of Physics. “The high-energy X-ray technology will allow us to see black holes that are buried deep inside their galaxies, hidden behind thick clouds of dust and gas. The goal is to unmask these black holes, study their host galaxies, and figure out how the black holes affect galaxy formation and evolution.”

Ballantyne has worked on the project, which is overseen by Fiona Harrison, a professor at the California Institute of Technology, since 2007. He and his peers have plotted three areas in the sky to survey, the largest of which spans approximately five full moons. Together, the surveys will uncover about 500 black holes, some of which have never been detected by any other telescope.

Seeing more means learning more, according to Ballantyne. He compares the study of black holes with learning about mankind.

“If you knew nothing about humans and looked at one person, you would quickly discover that we have two eyes, a nose and a mouth,” said Ballantyne. “But the deeper knowledge – traits such as aging, cultures – is only discovered by looking at a wide range of people. The more black holes we discover and study, the more we will understand about their roles in the cosmos.”

NuSTAR is the first telescope capable of focusing high-energy X-rays. It will also map supernova explosions and microflares on the surface of the sun. It is the first American high-energy telescope launched since 2008 and the last one for the foreseeable future. There are no other planned projects. 

NuSTAR will lift off aboard an airplane in the South Pacific. The plane will then launch a Pegasus rocket, which will carry the telescope into orbit. Images and data should be available for Ballantyne and his colleagues about a month after liftoff. Selected images and science stories will be made available for the public throughout the mission.

NuSTAR is a Small Explorer mission led by the California Institute of Technology and managed by NASA's Jet Propulsion Laboratory, both in Pasadena, Calif., for NASA's Science Mission Directorate. The spacecraft was built by Orbital Sciences Corporation, Dulles, Va. Its instrument was built by a consortium including Caltech; JPL; the University of California, Berkeley; Columbia University, New York; NASA's Goddard Space Flight Center in Greenbelt, Md.; the Danish Technical University in Denmark; Lawrence Livermore National Laboratory, Calif.; and ATK Aerospace Systems, Goleta, Calif. NuSTAR will be operated by UC Berkeley, with the Italian Space Agency providing its equatorial ground station located at Malindi, Kenya. The mission's outreach program is based at Sonoma State University, Calif. NASA's Explorer Program is managed by Goddard. JPL is managed by Caltech for NASA.

A new study shows that the availability of hydrogen plays a significant role in determining the chemical and structural makeup of graphene oxide, a material that has potential uses in nano-electronics, nano-electromechanical systems, sensing, composites, optics, catalysis and energy storage.

The study also found that after the material is produced, its structural and chemical properties continue to evolve for more than a month as a result of continuing chemical reactions with hydrogen.

Understanding the properties of graphene oxide – and how to control them – is important to realizing potential applications for the material. To make it useful for nano-electronics, for instance, researchers must induce both an electronic band gap and structural order in the material. Controlling the amount of hydrogen in graphene oxide may be the key to manipulating the material properties.

“Graphene oxide is a very interesting material because its mechanical, optical and electronic properties can be controlled using thermal or chemical treatments to alter its structure,” said Elisa Riedo, an associate professor in the School of Physics at the Georgia Institute of Technology. “But before we can get the properties we want, we need to understand the factors that control the material’s structure. This study provides information about the role of hydrogen in the reduction of graphene oxide at room temperature.”

The research, which studied graphene oxide produced from epitaxial graphene, was reported on May 6 in the journal Nature Materials. The research was sponsored by the National Science Foundation, the Materials Research Science and Engineering Center (MRSEC) at Georgia Tech, and by the U.S. Department of Energy.

(For the full article, please visit this page)

A new study shows that the availability of hydrogen plays a significant role in determining the chemical and structural makeup of graphene oxide, a material that has potential uses in nano-electronics, nano-electromechanical systems, sensing, composites, optics, catalysis and energy storage.

The study also found that after the material is produced, its structural and chemical properties continue to evolve for more than a month as a result of continuing chemical reactions with hydrogen.

Understanding the properties of graphene oxide – and how to control them – is important to realizing potential applications for the material. To make it useful for nano-electronics, for instance, researchers must induce both an electronic band gap and structural order in the material. Controlling the amount of hydrogen in graphene oxide may be the key to manipulating the material properties.

“Graphene oxide is a very interesting material because its mechanical, optical and electronic properties can be controlled using thermal or chemical treatments to alter its structure,” said Elisa Riedo, an associate professor in the School of Physics at the Georgia Institute of Technology. “But before we can get the properties we want, we need to understand the factors that control the material’s structure. This study provides information about the role of hydrogen in the reduction of graphene oxide at room temperature.”

The research, which studied graphene oxide produced from epitaxial graphene, was reported on May 6 in the journal Nature Materials. The research was sponsored by the National Science Foundation, the Materials Research Science and Engineering Center (MRSEC) at Georgia Tech, and by the U.S. Department of Energy.

Graphene oxide is formed through the use of chemical and thermal processes that mainly add two oxygen-containing functional groups to the lattice of carbon atoms that make up graphene: epoxide and hydroxyl species. The Georgia Tech researchers began their studies with multilayer expitaxial graphene grown atop a silicon carbide wafer, a technique pioneered by Walt de Heer and his research group at Georgia Tech. Their samples included an average of ten layers of graphene.

After oxidizing the thin films of graphene using the established Hummers method, the researchers examined their samples using X-ray photo-emission spectroscopy (XPS). Over about 35 days, they noticed the number of epoxide functional groups declining while the number of hydroxyl groups increased slightly. After about three months, the ratio of the two groups finally reached equilibrium.

“We found that the material changed by itself at room temperature without any external stimulation,” said Suenne Kim, a postdoctoral fellow in Riedo’s laboratory. “The degree to which it was unstable at room temperature was surprising.”

Curious about what might be causing the changes, Riedo and Kim took their measurements to Angelo Bongiorno, an assistant professor who studies computational materials chemistry in Georgia Tech’s School of Chemistry and Biochemistry. Bongiorno and graduate student Si Zhou studied the changes using density functional theory, which suggested that hydrogen could be combining with oxygen in the functional groups to form water. That would favor a reduction in the epoxide groups, which is what Riedo and Kim were seeing experimentally.

“Elisa’s group was doing experimental measurements, while we were doing theoretical calculations,” Bongiorno said. “We combined our information to come up with the idea that maybe there was hydrogen involved.”

The suspicions were confirmed experimentally, both by the Georgia Tech group and by a research team at the University of Texas at Dallas. This information about the role of hydrogen in determining the structure of graphene oxide suggests a new way to control its properties, Bongiorno noted.

“During synthesis of the material, we could potentially use this as a tool to change the structure,” he said. “By understanding how to use hydrogen, we could add it or take it out, allowing us to adjust the relative distribution and concentration of the epoxide and hydroxyl species which control the properties of the material.”

Riedo and Bongiorno acknowledge that their material – based on epitaxial graphene – may be different from the oxide produced from exfoliated graphene. Producing graphene oxide from flakes of the material involves additional processing, including dissolving in an aqueous solution and then filtering and depositing the material onto a substrate. But they believe hydrogen plays a similar role in determining the properties of exfoliated graphene oxide.

“We probably have a new new form of graphene oxide, one that may be more useful commercially, although the same processes should also be happening within the other form of graphene oxide,” said Bongiorno.

The next steps are to understand how to control the amount of hydrogen in epitaxial graphene oxide, and what conditions may be necessary to affect reactions with the two functional groups. Ultimately, that may provide a way to open an electronic band gap and simultaneously obtain a graphene-based material with electron transport characteristics comparable to those of pristine graphene.

“By controlling the properties of graphene oxide through this chemical and thermal reduction, we may arrive at a material that remains close enough to graphene in structure to maintain the order necessary for the excellent electronic properties, while having the band gap needed to create transistors,” Riedo said. “It could be that graphene oxide is the way to arrive at that type of material.”

Beyond those already mentioned, the paper’s authors included Yike Hu, Claire Berger and Walt de Heer from the School of Physics at Georgia Tech, and Muge Acik and Yves Chabal from the Department of Materials Science and Engineering at the University of Texas at Dallas.

This research was supported by the National Science Foundation under grants CMMI-1100290, DMR-0820382 and DMR-0706031, and by the U.S. Department of Energy’s Office of Basic Energy Sciences under grants DE-FG02-06ER46293 and DE-SC001951. The content is solely the responsibility of the principal investigators and does not necessarily represent the official views of the National Science Foundation or the Department of Energy.

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Writer: John Toon

Every year, Georgia Tech's Center for Enhanced Teaching and Learning (CETL) invites a small, multidisciplinary group of associate professors to become Hesburgh Award Teaching Fellows. These faculty members are nominated for this honor by their college and meet throughout spring semester to discuss innovative ways to improve student learning and to strengthen teaching on the Georgia Tech campus. Teaching Fellows receive a small stipend ($1000) to implement a project to improve student learning in a course during the following summer or fall semester.

Physics Professor Deirdre Shoemaker will use the funds toward the creation of a Relativity Virtual Lab in the Center for Relativistic Astrophyics.  The idea of the lab is to give visual and mathematical support to some of the more challenging topics in Special and General Relativity (like black holes and curved spacetime).  Just as we use labs in introductory physics to demonstrate important physical concepts, these labs will reinforce the student's understanding of gravity albeit virtually. Funds will support a student in helping write the software for the virtual lab.

Dr. Daniel Goldman, Assistant Professor in the School of Physics, has received the Young Faculty Award from the Defense Advanced Research Projects Agency (DARPA), an agency of the Department of Defense. Goldman received his DARPA award for his proposal, “Towards a Terramechanics of Heterogeneous Granular Substrates.”

The DARPA Young Faculty Award program identifies and engages rising research stars in junior faculty positions at U.S. academic institutions and exposes them to Department of Defense needs as well as DARPA’s program development process.

Goldman, who joined the Georgia Tech faculty in 2007, has made marked contributions to the discovery of the principles of locomotion on granular media and the biomechanics of locomotion of organisms and robots to address problems in nonequilibrium systems that involve interaction of matter with complex media.

Using lasers to excite just one atom from a cloud of ultra-cold rubidium gas, physicists have developed a new way to rapidly and efficiently create single photons for potential use in optical quantum information processing – and in the study of dynamics and disorder in certain physical systems.

The technique takes advantage of the unique properties of atoms that have one or more electrons excited to a condition of near-ionization known as the Rydberg state. Atoms in this highly excited state – with a principal quantum number greater than 70 – have exaggerated electromagnetic properties and interact strongly with one another. That allows one Rydberg atom to block the formation of additional excited atoms within an area of 10 to 20 microns.

That single Rydberg atom can then be converted to a photon, ensuring that – on average – only one photon is produced from a rubidium cloud containing hundreds of densely-packed atoms. Reliably producing a single photon with well known properties is important to several research areas, including quantum information systems.

The new technique was reported April 19 in Science Express, the rapid online publication of the journal Science. The research was supported by the National Science Foundation (NSF), and by the Air Force Office of Scientific Research (AFOSR).

“We are able to convert Rydberg excitations to single photons with very substantial efficiency, which allows us to prepare the state we want every time,” explained Alex Kuzmich, a professor in the School of Physics at the Georgia Institute of Technology. “This new system offers a fertile area for investigating entangled states of atoms, spin waves and photons. We hope this will be a first step toward doing a lot more with this system.”

For the full article, please visit this page.

Scientists have been squeezing the spin states of atoms for 15 years, but only for atoms that have just two relevant quantum states – known as spin ½ systems. In collections of those atoms, the spin states of the individual atoms can be added together to get a collective angular momentum that describes the entire system of atoms.

In the Bose-Einstein condensate atoms being studied by School of Physics Professor Michael Chapman’s group, the atoms have three quantum states, and their collective spin totals zero – not very helpful for describing systems. So Chapman and graduate students Chris Hamley, Corey Gerving, Thai Hoang and Eva Bookjans learned to squeeze a more complex measure that describes their system of spin 1 atoms: nematic tensor, also known as quadrupole.

For the full article, go here.

Using lasers to excite just one atom from a cloud of ultra-cold rubidium gas, physicists have developed a new way to rapidly and efficiently create single photons for potential use in optical quantum information processing – and in the study of dynamics and disorder in certain physical systems.

The technique takes advantage of the unique properties of atoms that have one or more electrons excited to a condition of near-ionization known as the Rydberg state. Atoms in this highly excited state – with a principal quantum number greater than 70 – have exaggerated electromagnetic properties and interact strongly with one another. That allows one Rydberg atom to block the formation of additional excited atoms within an area of 10 to 20 microns.

That single Rydberg atom can then be converted to a photon, ensuring that – on average – only one photon is produced from a rubidium cloud containing hundreds of densely-packed atoms. Reliably producing a single photon with well known properties is important to several research areas, including quantum information systems.

The new technique was reported April 19 in Science Express, the rapid online publication of the journal Science. The research was supported by the National Science Foundation (NSF), and by the Air Force Office of Scientific Research (AFOSR).

“We are able to convert Rydberg excitations to single photons with very substantial efficiency, which allows us to prepare the state we want every time,” explained Alex Kuzmich, a professor in the School of Physics at the Georgia Institute of Technology. “This new system offers a fertile area for investigating entangled states of atoms, spin waves and photons. We hope this will be a first step toward doing a lot more with this system.”

Kuzmich and co-author Yaroslav Dudin, a graduate research assistant, have been studying quantum information systems that rely on mapping information from atoms onto entangled pairs of photons. But the Raman scattering technique they have been using to create the photons was inefficient and unable to provide the number of entangled photons needed for complex systems.

“This new photon source is about a thousand times faster than existing systems,” Dudin said. “The numbers are very good for our first experimental implementation.”

To create a Rydberg atom, the researchers used lasers to illuminate a dense ensemble of several hundred rubidium 87 atoms that had been laser-cooled and confined in an optical lattice. The illumination boosted a single atom from the entire cloud into the Rydberg state. Atoms excited to the Rydberg state strongly interact with other Rydberg atoms, and under suitable conditions, modify the atomic level energies and prevent more than one atom from being transferred into this state – a phenomenon known as the Rydberg blockade.

Rydberg atoms show this strong interaction within a range of 10 to 20 microns. By limiting their starting ensemble of rubidium atoms to approximately that distance, Kuzmich and Dudin were able to ensure that no more than one such atom could form.

“The excited Rydberg atom needs space around it and doesn’t allow any other Rydberg atoms to come nearby,” Dudin explained. “Our ensemble has a limited volume, so we couldn’t fit more than one of these atoms into the space available.”

Kuzmich and Dudin have been using Rydberg atoms with a principal quantum number of approximately 100. These excited atoms are much larger – as much as a half-micron in diameter – than ground state rubidium atoms, which have a quantum number of 5 and a diameter of a few Angstroms.

Once a highly excited atom was created, the researchers used an additional laser field to convert the excitation into a quantum light field that has the same statistical properties as the excitation. Because the field was produced by a single Rydberg atom, it contained just one photon, which can be used in a variety of protocols.

For the Georgia Tech group, the next goal may be development of a quantum gate between light fields. The quantum gating of photons has been proposed and pursued by many research groups, so far unsuccessfully.

“If this can be realized, such quantum gates would allow us to deterministically create complex entangled states of atoms and light, which would add valuable capabilities to the fields of quantum networks and computing,” Kuzmich said. “Our works points in this direction.”

Beyond quantum information systems, the new single-photon system could also help scientists investigating other areas of physics.

“Our results also hold promise for studies of dynamics and disorder in many-body systems with tunable interactions,” Kuzmich explained. “In particular, translational symmetry breaking, phase transitions and non-equilibrium many-body physics could be investigated in the future using strongly-coupled Rydberg excitations of an atomic gas.”

The single-photon work complements research being done in the Kuzmich lab on long-lived quantum memories. A new Air Force Office of Scientific Research Multidisciplinary University Research Initiative (MURI) was recently awarded to a consortium of seven U.S. universities that will work together to determine the best approach for generating quantum memories based on interaction between light and matter. Georgia Tech leads the MURI.

“With this new work, we have demonstrated a new, deterministic source of single photons,” Kuzmich said. “In its first experimental realization, it already out-performs other types of single photons that have been pursued during the past decade around the world, including in our group. With further increases in efficiency and generation rate – and integration with long-lived quantum memories being developed in related work – such a single-photon source may make possible optical quantum information processing.”

Research News & Publications Office
Georgia Institute of Technology
75 Fifth Street, N.W., Suite 314
Atlanta, Georgia 30308 USA

Media Relations Contacts: John Toon (404-894-6986)(jtoon@gatech.edu) or Abby Robinson (404-385-3364)(abby@innovate.gatech.edu).

Writer: John Toon

It's awards season! Congratulations to the following Physics undergraduate students for their outstanding academic achievements:

H. Fukuyo Outstanding Physics Undergraduate Award to Luis Saldana: award of $3,000 given to the most outstanding undergraduate academic student in the School of Physics.

H. Fukuyo Memorial Scholarship Award in Physics to James Andrews and Zachary Taylor: this award consists of $3,000 and the engraving of the recipient's name on a plaque in the School of Physics.

The Joyce M. and Glenn A. Burdick Award to Alexander Tarr: recognizes rising seniors in the School of Physics who demonstrate scholastic achievement and leadership, and possess characteristics that embody the mission of Georgia Tech. Award of $2,000.

Although cosmic rays were discovered 100 years ago, their origin remains one of the most enduring mysteries in physics. Now, the IceCube Neutrino Observatory, a massive detector in Antarctica, is honing in on how the highest energy cosmic rays are produced.

Cosmic rays are electrically charged particles, such as protons, that strike Earth from all directions, with energies up to one hundred million times higher than those created in man-made accelerators. The intense conditions needed to generate such energetic particles have focused physicists’ interest on two potential sources: the massive black holes at the centers of active galaxies, and the exploding fireballs observed by astronomers as gamma ray bursts (GRBs).

IceCube is using neutrinos, which are believed to accompany cosmic ray production, to explore these theories. In a paper published in the April 19 issue of the journal Nature, the IceCube collaboration – which includes a Georgia Institute of Technology scientist -- describes a search for neutrinos emitted from 300 gamma ray bursts observed, most recently in coincidence with the SWIFT and Fermi satellites, between May 2008 and April 2010. Surprisingly, they found none - a result that contradicts 15 years of predictions and challenges one of the two leading theories for the origin of the highest energy cosmic rays.

“The result of this neutrino search is significant because for the first time we have an instrument with sufficient sensitivity to open a new window on cosmic ray production and the interior processes of GRBs,” said IceCube spokesperson and University of Maryland physics professor Greg Sullivan. “The unexpected absence of neutrinos from GRBs has forced a re-evaluation of the theory for production of cosmic rays and neutrinos in a GRB fireball and possibly the theory that high energy cosmic rays are generated in fireballs.”

IceCube is a high energy neutrino telescope at the geographical South Pole in Antarctica, operated by a collaboration of 250 physicists and engineers from the United States, Germany, Sweden, Belgium, Switzerland, Japan, Canada, New Zealand, Australia and Barbados. The IceCube Neutrino Observatory was built under a National Science Foundation (NSF) Major Research Equipment and Facilities Construction grant, with assistance from partner funding agencies around the world. The NSF Office of Polar Programs continues to support the project with a maintenance and operations grant. Construction was finished in December 2010.

“One of the main objectives of IceCube is to search for the sources of the highest energy cosmic rays,” explained Ignacio Taboada, an assistant professor in the Georgia Tech School of Physics who has been involved in IceCube since its planning stages. “Gamma ray bursts have always been high on the list of potential sources for cosmic rays. Though not completely ruled out, the mechanisms by which GRBs could produce these cosmic rays are now significantly constrained by these results. We will keep looking for the sources, and our chances of finding them will increase as we accumulate more data to improve our sensitivity.”

IceCube observes neutrinos by detecting the faint blue light produced in neutrino interactions in ice. Neutrinos are of a ghostly nature; they can easily travel through people, walls, or the planet Earth. To compensate for the antisocial nature of neutrinos and detect their rare interactions, IceCube is built on an enormous scale. One cubic kilometer of glacial ice, enough to fit the great pyramid of Giza 400 times, is instrumented with 5,160 optical sensors embedded up to 2.5 kilometers deep in the ice.

GRBs, the universe’s most powerful explosions, are usually first observed by satellites using X-rays and/or gamma rays. GRBs are seen about once per day, and are so bright that they can be seen from half way across the visible universe. The explosions usually last only a few seconds, and during this brief time they can outshine everything else in the universe.

“Although we have not discovered where cosmic rays come from, we have taken a major step towards ruling out one of the leading predictions,” said IceCube principal investigator and University of Wisconsin - Madison physics professor Francis Halzen.

Improved theoretical understanding and more data from the compete IceCube detector will help scientists better understand the mystery of cosmic ray production. IceCube is currently collecting more data with the finalized, better calibrated, and better understood detector.

For more information about IceCube, visit www.icecube.wisc.edu.