Tag: UC Berkeley

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Founded in the wake of the gold rush by leaders of the newly established 31st state, the University of California’s flagship campus at Berkeley has become one of the preeminent universities in the world. Its early guiding lights, charged with providing education (both “practical” and “classical”) for the state’s people, gradually established a distinguished faculty (with 22 Nobel laureates to date), a stellar research library, and more than 350 academic programs.

From “Physics”: “New Electron Trap Might Help Quantum Computers”

About Physics

From “Physics”

January 29, 2021
Philip Ball

Long-time trapping of a single electron could allow the particle to be used as an efficient quantum bit.

The eye of the trap. Theory predicts the potential energy surface for a slice through the three layers of circuit boards that make up the trap, showing a deep valley (central blue region, about a millimeter wide) to hold the electron. Gray hashed areas are the board cross sections, and yellow lines represent metal electrodes.

Quantum computers use quantum bits (qubits) that, in addition to encoding the states 1 and 0, can be placed in combinations of the two. Several types of qubits are currently used, and now a research team has demonstrated that single electrons can be trapped effectively enough to potentially serve as a new, more efficient type of qubit [1]. The researchers trapped electrons for a record time of 1 s. They say their results imply that electron qubits could be used to make faster quantum computers.

Qubits made from superconducting circuits or from single trapped ions—today’s most practical qubit types—have inherent limitations, such as limits on the speed with which they can be switched from 1 to 0. A trapped electron could act as a simple qubit based on its spin state—up or down. Hartmut Häffner of the University of California at Berkeley says that electrons should be able to switch 100 times faster than trapped-ion qubits and should be less susceptible to the environmental noise that degrades the performance of superconducting qubits. So, in principle, trapped electrons could yield fast and high-fidelity quantum computers.

However, trapping single electrons for long times isn’t easy. It has been achieved before in configurations that would not be good for a qubit [2, 3]—for example, using strong magnetic fields that would interfere with the qubit’s operation. Single ion qubits, meanwhile, have usually been held in Paul traps, which use oscillating electric fields that can be generated by electrodes in a chip-based circuit [4].

To trap electrons this way, Häffner and colleagues created a microwave-frequency Paul trap that fits onto a three-layer, 5- by 10-cm circuit board containing a 1-mm-wide slot where the trapped electron floats. Starting with a low-energy electron helps to increase its lifetime in the trap. To generate such slow-moving (cold) electrons, the researchers adapted a procedure previously used to produce ions efficiently. The team hit a beam of calcium atoms with two lasers, one tuned to promote an electron to a highly excited state and the second tuned to provide just enough energy to exceed the atom’s ionization threshold.

Electrons in the void. This credit-card-sized circuit board, shown in the experiment’s vacuum chamber, houses an electric quadrupole trap that can hold individual electrons for more than a second. By entangling them and encoding quantum information in their spins, the electrons might eventually be used for quantum computing. Credit: C. Matthiesen/UC Berkeley.

The researchers found that some electrons could be kept in their trap for more than a second at room temperature; they should last even longer at the low temperatures at which a quantum computer is likely to operate. On the other hand, around three-quarters of the electrons were lost within 0.1 s. The researchers hope to improve the trapping efficiency once they have a better understanding of the loss mechanisms.

With a trapped electron qubit, readout of quantum information could be done using magnetic fields to sense the spins. Häffner and co-workers have already proposed a procedure of this sort, using oscillating magnetic fields to separate spin-up and spin-down electrons into streams that could be sensed by electrodes [5]. Putting that idea into practice will be one of the next steps, Häffner says, along with demonstrating a logic operation for a simple two-qubit quantum gate, also using magnetic fields to manipulate the spins.

“Nothing was really much more difficult than [using] a standard Paul trap,” says Häffner. Team member Clemens Matthiesen admits that he shared some of the skepticism of others about whether electrons could be trapped for long enough. “But you can’t know until actually trying the experiment,” he says, “and I was somewhat shocked by how well it worked.” One key to the success was using the calcium ionization technique to create electrons having sufficiently low energy, Häffner says.

“I like the results very much,” says Ferdinand Schmidt-Kaler of the University of Mainz (DE), who has been working with other kinds of electron traps. He agrees that electrons’ high switching speed is an advantage over trapped ions and that using a chip-based trap—the next step in miniaturization of the new trap’s circuitry—could make practical implementation easier.

Chris Monroe of the University of Maryland, College Park, who has worked with ion-based qubits in quantum-computing devices, says that the work is “compelling” but stresses that there are “lots of remaining challenges ahead” before it becomes a viable technology. Electrons have just one internal “knob”—their spin—which can’t be manipulated simply with laser beams for read and write operations, as ion states can be. However, Häffner says that using chip-based magnetic operations for this, rather than lasers, could actually simplify the technology. Monroe adds that combining elements of electronic systems with those of trapped ions means that electron qubits “can hopefully adopt the best of both worlds.”

References

C. Matthiesen et al., “Trapping electrons in a room-temperature microwave Paul trap,” Phys. Rev. X 11, 011019 (2021).
D. Wineland et al., “Monoelectron oscillator,” Phys. Rev. Lett. 31, 1279 (1973).
G. Koolstra et al., “Coupling a single electron on superfluid helium to a superconducting resonator,” Nat. Commun. 10, 5323 (2019).
K. R. Brown et al., “Co-designing a scalable quantum computer with trapped atomic ions,” npj Quantum Inf. 2, 1 (2016).
P. Peng et al., “Spin readout of trapped electron qubits,” Phys. Rev. A 95, 012312 (2017).

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From NASA/ESA Hubble Telescope

Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries. Physics provides a much-needed guide to the best in physics, and we welcome your comments (physics@aps.org).

From NASA/ESA Hubble Telescope: “Hubble Pins Down Weird Exoplanet with Far-Flung Orbit”

December 10, 2020

Media Contacts:
Ann Jenkins
Space Telescope Science Institute, Baltimore, Maryland
410-338-4488
jenkins@stsci.edu

Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514
villard@stsci.edu

Science Contacts:
Meiji Nguyen
University of California, Berkeley, California
meiji274@berkeley.edu

Robert De Rosa
European Southern Observatory, Santiago, Chile
rderosa@eso.org

Paul Kalas
University of California, Berkeley, California
kalas@berkeley.edu

About This Image
This Hubble Space Telescope image shows one possible orbit (dashed ellipse) of the 11-Jupiter-mass exoplanet HD 106906 b. This remote world is widely separated from its host stars, whose brilliant light is masked here to allow the planet to be seen. The planet resides outside its system’s circumstellar debris disk, which is akin to our own Kuiper Belt of small, icy bodies beyond Neptune. The disk itself is asymmetric and distorted, perhaps due to the gravitational tug of the wayward planet. Other points of light in the image are background stars.
Credit: NASA, ESA, M. Nguyen (University of California, Berkeley), R. De Rosa (European Southern Observatory), and P. Kalas (University of California, Berkeley and SETI Institute)

About This Image
The 11-Jupiter-mass exoplanet called HD 106906 b, shown in this artist’s illustration, occupies an unlikely orbit around a double star 336 light-years away. It may be offering clues to something that might be much closer to home: a hypothesized distant member of our solar system dubbed “Planet Nine.” This is the first time that astronomers have been able to measure the motion of a massive Jupiter-like planet that is orbiting very far away from its host stars and visible debris disk. Credit: NASA, ESA, M. Kornmesser (ESA/Hubble).

About This Image
This graphic shows how the exoplanet HD 106906 b may have evolved over time, arriving at its current, widely separated, eccentric and highly misaligned orbit. (1) The planet formed much closer to its stars, inside a circumstellar disk of gas and dust. Drag from the disk caused the planet’s orbit to decay, forcing it to spiral inward toward its stellar pair. (2) The gravitational effects from the host stars then kicked the planet out onto an unstable orbit that almost threw it out of the system and into the void of interstellar space. (3) A passing star from outside the system stabilized HD 106906 b’s orbit and prevented the planet from leaving its home system. Credit: NASA,ESA, and L. Hustak STSCI.

About This Image
This Hubble Space Telescope image shows the environment around double star HD 106906. The brilliant light from these stars is masked here to allow fainter features in the system to be seen. The stars’ circumstellar disk is asymmetric and distorted, perhaps due to the gravitational tug of the wayward planet HD 106906 b, which is in a very large and elongated orbit. Credit:
NASA, ESA, M. Nguyen (University of California, Berkeley), R. De Rosa (European Southern Observatory), and P. Kalas (University of California, Berkeley and SETI Institute).

About This Video
This video shows the possible orbit of exoplanet HD 106906 b. The light from the twin stars has been masked to block their bright glare, allowing the Hubble Space Telescope to see the circumstellar disk and exoplanet. The planet resides outside its system’s circumstellar debris disk, which is akin to our own Kuiper Belt. The second part of the video shows a simulation of how the planet orbits counterclockwise around the entire system as seen from Earth. Credit: NASA, ESA, P. Kalas (University of California, Berkeley and SETI Institute), and J. DePasquale (STScI).

A planet in an unlikely orbit around a double star 336 light-years away may offer a clue to a mystery much closer to home: a hypothesized, distant body in our solar system dubbed “Planet Nine.”

This is the first time that astronomers have been able to measure the motion of a massive Jupiter-like planet that is orbiting very far away from its host stars and visible debris disk. This disk is similar to our Kuiper Belt of small, icy bodies beyond Neptune. In our own solar system, the suspected Planet Nine would also lie far outside of the Kuiper Belt on a similarly strange orbit. Though the search for a Planet Nine continues, this exoplanet discovery is evidence that such oddball orbits are possible.

“This system draws a potentially unique comparison with our solar system,” explained the paper’s lead author, Meiji Nguyen of the University of California, Berkeley. “It’s very widely separated from its host stars on an eccentric and highly misaligned orbit, just like the prediction for Planet Nine. This begs the question of how these planets formed and evolved to end up in their current configuration.”

The system where this gas giant resides is only 15 million years old. This suggests that our Planet Nine—if it does exist—could have formed very early on in the evolution of our 4.6-billion-year-old solar system.

An Extreme Orbit

The 11-Jupiter-mass exoplanet called HD 106906 b was discovered in 2013 with the Magellan Telescopes at the Las Campanas Observatory in the Atacama Desert of Chile.

Carnegie 6.5 meter Magellan Baade and Clay Telescopes located at Carnegie’s Las Campanas Observatory, Chile. over 2,500 m (8,200 ft) high.

However, astronomers did not know anything about the planet’s orbit. This required something only the Hubble Space Telescope could do: collect very accurate measurements of the vagabond’s motion over 14 years with extraordinary precision. The team used data from the Hubble archive that provided evidence for this motion.

The exoplanet resides extremely far from its host pair of bright, young stars—more than 730 times the distance of the Earth from the Sun, or nearly 6.8 billion miles. This wide separation made it enormously challenging to determine the 15,000-year-long orbit in such a relatively short time span of Hubble observations. The planet is creeping very slowly along its orbit, given the weak gravitational pull of its very distant parent stars.

The Hubble team was surprised to find that the remote world has an extreme orbit that is very misaligned, elongated and external to the debris disk that surrounds the exoplanet’s twin host stars. The debris disk itself is very unusual-looking, perhaps due to the gravitational tug of the wayward planet.

How Did It Get There?

So how did the exoplanet arrive at such a distant and strangely inclined orbit? The prevailing theory is that it formed much closer to its stars, about three times the distance that the Earth is from the Sun. But drag within the system’s gas disk caused the planet’s orbit to decay, forcing it to migrate inward toward its stellar pair. The gravitational effects from the whirling twin stars then kicked it out onto an eccentric orbit that almost threw it out of the system and into the void of interstellar space. Then a passing star from outside the system stabilized the exoplanet’s orbit and prevented it from leaving its home system.

Using precise distance and motion measurements from the European Space Agency’s Gaia survey satellite, candidate passing stars were identified in 2019 by team members Robert De Rosa of the European Southern Observatory in Santiago, Chile and Paul Kalas of the University of California.

A Messy Disk

In a study published in 2015, Kalas led a team that found circumstantial evidence for the runaway planet’s behavior: the system’s debris disk is strongly asymmetric, rather than being a circular “pizza pie” distribution of material. One side of the disk is truncated relative to the opposite side, and it is also disturbed vertically rather than being restricted to a narrow plane as seen on the opposite side of the stars.

“The idea is that every time the planet comes to its closest approach to the binary star, it stirs up the material in the disk,” explains De Rosa. “So every time the planet comes through, it truncates the disk and pushes it up on one side. This scenario has been tested with simulations of this system with the planet on a similar orbit—this was before we knew what the orbit of the planet was.”

“It’s like arriving at the scene of a car crash, and you’re trying to reconstruct what happened,” explained Kalas. “Is it passing stars that perturbed the planet, then the planet perturbed the disk? Is it the binary in the middle that first perturbed the planet, and then it perturbed the disk? Or did passing stars disturb both the planet and disk at the same time? This is astronomy detective work, gathering the evidence we need to come up with some plausible storylines about what happened here.”

A Planet Nine Proxy?

This scenario for HD 106906 b’s bizarre orbit is similar in some ways to what may have caused the hypothetical Planet Nine to end up in the outer reaches of our own solar system, well beyond the orbit of the other planets and beyond the Kuiper Belt.

Planet Nine could have formed in the inner solar system and been kicked out by interactions with Jupiter. However, Jupiter—the proverbial 800-pound gorilla in our solar system—would very likely have flung Planet Nine far beyond Pluto. Passing stars may have stabilized the orbit of the kicked-out planet by pushing the orbit path away from Jupiter and the other planets in the inner solar system.

“It’s as if we have a time machine for our own planetary system going back 4.6 billion years to see what may have happened when our young solar system was dynamically active and everything was being jostled around and rearranged,” said Kalas.

To date, astronomers only have circumstantial evidence for Planet Nine. They’ve found a cluster of small celestial bodies beyond Neptune that move in unusual orbits compared with the rest of the solar system. This configuration, some astronomers say, suggests these objects were shepherded together by the gravitational pull of a huge, unseen planet. An alternative theory is that there is not one giant perturbing planet, but instead the imbalance is due to the combined gravitational influence of multiple, much smaller objects. Another theory is that Planet Nine does not exist at all and the clustering of smaller bodies may be just a statistical anomaly.

A Target for the Webb Telescope

Scientists using NASA’s upcoming James Webb Space Telescope plan to get data on HD 106906 b to understand the planet in detail.

NASA James Webb Space Telescope annotated.

“One question you could ask is: Does the planet have its own debris system around it? Does it capture material every time it goes close to the host stars? And you’d be able to measure that with the thermal infrared data from Webb,” said De Rosa. “Also, in terms of helping to understand the orbit, I think Webb would be useful for helping to confirm our result.”

Because Webb is sensitive to smaller, Saturn-mass planets, it may be able to detect other exoplanets that have been ejected from this and other inner planetary systems. “With Webb, we can start to look for planets that are both a little bit older and a little bit fainter,” explained Nguyen. The unique sensitivity and imaging capabilities of Webb will open up new possibilities for detecting and studying these unconventional planets and systems.

The team’s findings appear in the December 10, 2020 edition of The Astronomical Journal.

See the full article here .

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Major Instrumentation

Wide Field Camera 3 [WFC3]

Advanced Camera for Surveys [ACS]

NASA Hubble Advanced Camera for Surveys.

Cosmic Origins Spectrograph [COS]

NASA Hubble Cosmic Origins Spectrograph.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

From UC Berkeley: “Active volcanoes feed Io’s sulfurous atmosphere”

October 21, 2020
Robert Sanders
rlsanders@berkeley.edu

A composite image of Io in front of a Hubble Space Telescope photo of Jupiter. The observations for the first time show plumes of sulfur dioxide (yellow) rising up from Io’s volcanoes. Credit: ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello; NASA/ESA.

The atmosphere on Jupiter’s moon Io is a witches’ brew, composed primarily of the sulfurous exhalations of more than 400 volcanoes that dot the surface.

Until now, however, it has been unclear whether volcanoes spewing hot sulfur dioxide (SO2) are the main contributors to the atmosphere, or whether the main component is the accumulated cold SO2, much of which is frozen on the surface, but in sunlight evaporates or sublimates into the atmosphere.

New observations with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, led by astronomer Imke de Pater of the University of California, Berkeley, partially resolve that question.

ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres.

“It was not known which process drives the dynamics in Io’s atmosphere,” said de Pater, who is a Professor of the Graduate School in the departments of astronomy and of earth and planetary science at UC Berkeley. “Is it volcanic activity, or gas that sublimates from the icy surface when Io is in sunlight? What we show is that, actually, volcanoes do have a large impact on the atmosphere.“

As the most volcanically active moon in our solar system, Io (“EYE oh”) provides a laboratory for exotic environments unlike anything on Earth. And since we’re unable to probe inside Io, the atmosphere — about a billion times thinner than Earth’s atmosphere — provides a window into the moon’s roiling interior and the internal magma reservoirs feeding the volcanoes.

With no nearby satellite currently observing the moon — NASA’s Juno mission focuses primarily on Jupiter and will end next July — astronomers like de Pater must rely on Earth-based telescopes to probe the atmosphere.

She has been observing Io’s atmosphere for 30 years with radio telescopes like ALMA and optical and infrared telescopes, primarily the Keck telescopes in Hawaii.

Keck Observatory, operated by Caltech and the University of California, Maunakea Hawaii USA, altitude 4,207 m (13,802 ft).

One surprise from the new observations is that the atmosphere becomes dramatically unstable when Io passes through Jupiter’s shadow every 42 hours as it orbits the planet. In a paper accepted for publication in the Planetary Science Journal, de Pater and her colleagues report that the radio emissions from sulfur dioxide (SO2) gas dropped exponentially as Io was eclipsed by Jupiter on March 20, 2018, indicating that the lower atmosphere — below 10 to 20 kilometers in altitude — essentially collapsed, quickly freezing out onto the surface.

This video shows images of Jupiter’s moon Io in radio (obtained by ALMA) and optical light (from the Voyager 1 and Galileo missions) as Io is eclipsed by Jupiter and comes out of eclipse. These radio images for the first time show plumes of sulfur dioxide (in yellow) rise up from the volcanoes on Io. [Video courtesy of ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello; NASA]

Although Io’s surface is always cold — about 150 degrees Celsius below freezing, or -230 F — a further drop in temperature by a few tens of degrees, down to -270 F, brings the temperature below the freezing point of SO2.

As the moon reemerged from Jupiter’s shadow during observations on Sept. 2 and 11 in 2018, the cold sulfur dioxide emissions returned within about 10 minutes.

“As soon as Io gets into sunlight, the temperature increases, and you get all this SO2 ice subliming into gas, and you reform the atmosphere in about 10 minutes’ time, faster than what models had predicted,” said de Pater.

She noted that not all the cold SO2 froze out as the temperature dropped in Jupiter’s shadow. During the eclipse, in addition to abundant SO2 gas over some volcanoes, ALMA also detected low levels of SO2 globally in Io’s atmosphere, suggesting that many unseen volcanoes — so-called stealth volcanoes, because they emit no smoke or other particulates that can be easily seen — are constantly spewing SO2 into the atmosphere that remains too warm to condense.

There were also hints of stealth volcanism in observations reported by de Pater and her colleagues in July, based on Keck observations. They saw widespread sulfur monoxide (SO) gas in the atmosphere — not, as expected, only over active volcanoes. As de Pater shows in her new paper, SO is likely produced when sunlight breaks the sulfur-oxygen bond in SO2 that has been ejected hundreds of kilometers above the surface.

“The SO2 that we see with ALMA when Io is in eclipse is at a very low level, and we can’t say if that is stealth volcanism or caused by SO2 not completely condensing out,” she said. “But then, when we looked at the SO with Keck, we can only explain the SO emissions, which are widespread on the surface, through this stealth volcanism, because excitation of the SO requires a very high temperature.”

Io in eclipse

With such a thin atmosphere, Io is exposed to the cold of space, as well as to the hot plasma around Jupiter. The tidal tug that Jupiter and two of its largest moons, Ganymede and Europa, exert on Io heats the moon’s interior, creating the volcanoes that bathe the surface in hot sulfur dioxide fumes. Io’s largest volcano, Loki Patera, spans more than 200 kilometers (124 miles).

The volcanic SO2 eventually condenses on the surface to form a thick frozen layer of sulfur dioxide ice, recently mapped globally by de Pater and her colleagues. This frozen SO2, often overlain by a layer of volcanic dust, is what gives Io its characteristic yellow, white, orange and red colors.

Though the dominance of SO2 in Io’s atmosphere was well known — de Pater was a member of the first team to observe global SO2 in 1990 — it was still unclear whether recently emitted hot SO2 or sublimation from the accumulated SO2 ice (referred to as cold SO2) dominated the atmosphere.

To disentangle the contributions of hot and cold SO2, de Pater and her colleagues, including Statia Luszcz-Cook from Columbia University in New York and Katherine de Kleer of the California Institute of Technology, chose to observe Io during its transition from sunlight into darkness during an eclipse and again when it reemerged into the light from eclipse. Because of the alignment of Io and Earth relative to Jupiter, it’s impossible to observe both entry and exit of Jupiter’s moon from the same eclipse, so the two observations took place six months apart.

“When Io passes into Jupiter’s shadow, and is out of direct sunlight, it is too cold for sulfur dioxide gas, and it condenses onto Io’s surface. During that time, we can only see volcanically-sourced sulfur dioxide. We can, therefore, see exactly how much of the atmosphere is impacted by volcanic activity,” Luszcz-Cook said.

Thanks to ALMA’s exquisite resolution and sensitivity, the astronomers could, for the first time, clearly see the plumes of SO2 and SO rise up from the volcanoes, two of which — Karei Patera and Daedalus Patera — were erupting in March, while a third volcano was active in September. Based on the snapshots, they calculated that active volcanoes directly produce 30% to 50% of Io’s atmosphere.

The ALMA images also showed a third gas coming out of volcanoes: potassium chloride (KCl). Both KCl and sodium chloride — NaCl, or common table salt — are common components of magma.

“We see KCl in volcanic regions where we do not see SO2 or SO,” said Luszcz-Cook. “This is strong evidence that the magma reservoirs are different under different volcanoes.”

“By studying Io’s atmosphere and volcanic activity, we can understand more about the volcanoes, the tidal heating process and Io’s interior,” added de Kleer.

De Pater and her colleagues also hope to observe Io at other radio wavelengths that can probe several inches below the surface, potentially revealing the content and temperature of the magma underlying the volcanoes.

A big unknown remains the temperature in Io’s lower atmosphere. In future research, the astronomers hope to measure this with ALMA.

“To measure the temperature of Io’s atmosphere, we need to obtain a higher resolution in our observations, which requires that we observe the moon for a longer period of time. We can only do this when Io is in sunlight, since it does not spend much time in eclipse,” said de Pater. “During such an observation, Io will rotate by tens of degrees. We will need to apply software that helps us make unsmeared images. We have done this previously with radio images of Jupiter made with ALMA and the Very Large Array.”

Other co-authors of the paper reporting ALMA observations are Patricio Rojo of the Universidad de Chile in Santiago, Erin Redwing of UC Berkeley and Arielle Moullet of the NASA Ames Research Center in Moffett Field, California.

The research was funded by the National Science Foundation (AST-1313485). The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities Inc.

RELATED INFORMATION

ALMA Observations of Io Going into and Coming out of Eclipse
The Planetary Science Journal

High Spatial and Spectral Resolution Observations of the Forbidden 1.707 μm Rovibronic SO Emissions on Io: Evidence for Widespread Stealth Volcanism
The Planetary Science Journal

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From UC Berkeley and Lawrence Berkeley National Laboratory: “Jennifer Doudna Wins 2020 Nobel Prize in Chemistry”

From Lawrence Berkeley National Laboratory

and

October 7, 2020
Theresa Duque
media@lbl.gov

Jennifer Doudna (Credit: UC Berkeley)

Biochemist Jennifer Doudna, a professor at UC Berkeley and faculty scientist at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), is co-winner of the 2020 Nobel Prize in Chemistry for “the development of a method for genome editing.” [She now gets her own parking spot in the parking lot reserved for Nobel Prize winners.]

UC Berkeley parking lot for Nobel Prize winners.

The bacterial enzyme Cas9 is the engine of RNA-programmed genome engineering in human cells. Credit: Graphic by Jennifer Doudna/UC Berkeley.

UC Berkeley 2020 Nobel Press Conference

She shares the Nobel Prize with co-discoverer Emmanuelle Charpentier, who currently serves as the scientific and managing director of the Max Planck Unit for the Science of Pathogens in Berlin. Together, they form the first all-woman research team to win a Nobel Prize.

“On behalf of the Berkeley Lab community, I extend my warmest congratulations to Jennifer Doudna for receiving the Nobel Prize in Chemistry. She is an exceptional scientist, and her groundbreaking research will inspire the next generation of scientists to take on challenges that both push the boundaries of knowledge and benefit humanity,” said Berkeley Lab Director Mike Witherell.

The discovery of the CRISPR-Cas9 genetic engineering technology has radically changed genomics research. This genome-editing technology enables scientists to change or remove genes quickly, with a precision only dreamed of just a few years ago. Labs worldwide have redirected the course of their research to incorporate this new tool, with huge implications across biology, agriculture, and medicine.

Doudna is a faculty scientist in Berkeley Lab’s Molecular Biophysics and Integrated Bioimaging Division; a professor of molecular and cell biology, and chemistry, at UC Berkeley; and an investigator at the Howard Hughes Medical Institute.

Foundational Berkeley Lab research

Doudna’s interest in gene editing can be traced to her research as a doctoral student at Harvard Medical School, when she designed a self-replicating RNA. As a research fellow at the University of Colorado at Boulder, she began crystallizing RNA so that she could study its structure and understand the physical basis of catalysis. While on the faculty at Yale University, she continued her study of catalytic RNA. When she joined UC Berkeley and Berkeley Lab in 2002, she pursued her interest in how RNA molecules decide what genetic information gets disseminated in cells.

In 2008, Doudna’s nascent research on CRISPR RNA strands and the Cas1 protein was funded by a U.S. Department of Energy (DOE) Laboratory Directed Research and Development (LDRD) Program through her Berkeley Lab affiliation. Established by Congress in 1991, the LDRD program has helped the U.S. remain at the forefront of technology through the innovative, multidisciplinary research of the DOE national labs.

Building upon findings from this early work and other investigations, in 2012, Doudna and Charpentier’s research team detailed the underlying mechanisms of the CRISPR-Cas9 system – a component of the bacterial immune system that defends against invading viruses – and explained how it can be programmed to cut DNA at a target sequence. This seminal work was published in the journal Science.

Today, Doudna and Charpentier’s Nobel Prize-winning CRISPR-Cas9 technology is the basis of many promising medical technologies, including tools to diagnose and treat disease, and has many applications for the development of improved crops, biofuels, and bioproducts.

With Doudna’s award, Berkeley Lab scientists and research have now been recognized with 14 Nobel Prizes.

See the full article here .

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Bringing Science Solutions to the World
In the world of science, Lawrence Berkeley National Laboratory (Berkeley Lab) is synonymous with “excellence.” Thirteen Nobel prizes are associated with Berkeley Lab. Seventy Lab scientists are members of the National Academy of Sciences (NAS), one of the highest honors for a scientist in the United States. Thirteen of our scientists have won the National Medal of Science, our nation’s highest award for lifetime achievement in fields of scientific research. Eighteen of our engineers have been elected to the National Academy of Engineering, and three of our scientists have been elected into the Institute of Medicine. In addition, Berkeley Lab has trained thousands of university science and engineering students who are advancing technological innovations across the nation and around the world.

Berkeley Lab is a member of the national laboratory system supported by the U.S. Department of Energy through its Office of Science. It is managed by the University of California (UC) and is charged with conducting unclassified research across a wide range of scientific disciplines. Located on a 202-acre site in the hills above the UC Berkeley campus that offers spectacular views of the San Francisco Bay, Berkeley Lab employs approximately 3,232 scientists, engineers and support staff. The Lab’s total costs for FY 2014 were $785 million. A recent study estimates the Laboratory’s overall economic impact through direct, indirect and induced spending on the nine counties that make up the San Francisco Bay Area to be nearly $700 million annually. The Lab was also responsible for creating 5,600 jobs locally and 12,000 nationally. The overall economic impact on the national economy is estimated at $1.6 billion a year. Technologies developed at Berkeley Lab have generated billions of dollars in revenues, and thousands of jobs. Savings as a result of Berkeley Lab developments in lighting and windows, and other energy-efficient technologies, have also been in the billions of dollars.

Berkeley Lab was founded in 1931 by Ernest Orlando Lawrence, a UC Berkeley physicist who won the 1939 Nobel Prize in physics for his invention of the cyclotron, a circular particle accelerator that opened the door to high-energy physics. It was Lawrence’s belief that scientific research is best done through teams of individuals with different fields of expertise, working together. His teamwork concept is a Berkeley Lab legacy that continues today.

A U.S. Department of Energy National Laboratory Operated by the University of California.

From UC Berkeley and Lawrence Berkeley National Laboratory: “Metal wires of carbon complete toolbox for carbon-based computers”

Lawrence Berkeley National Laboratory

and

September 24, 2020
Robert Sanders
rlsanders@berkeley.edu

Scanning tunneling microscope image of wide-band metallic graphene nanoribbon (GNR). Each cluster of protrusions corresponds to a singly-occupied electron orbital. The formation of a pentagonal ring near each cluster leads to a more than tenfold increase in the conductivity of metallic GNRs. The GNR backbone has a width of 1.6 nanometers. (UC Berkeley image by Daniel Rizzo)

Transistors based on carbon rather than silicon could potentially boost computers’ speed and cut their power consumption more than a thousandfold — think of a mobile phone that holds its charge for months — but the set of tools needed to build working carbon circuits has remained incomplete until now.

A team of chemists and physicists at the University of California, Berkeley, has finally created the last tool in the toolbox, a metallic wire made entirely of carbon, setting the stage for a ramp-up in research to build carbon-based transistors and, ultimately, computers.

“Staying within the same material, within the realm of carbon-based materials, is what brings this technology together now,” said Felix Fischer, UC Berkeley professor of chemistry, noting that the ability to make all circuit elements from the same material makes fabrication easier. “That has been one of the key things that has been missing in the big picture of an all-carbon-based integrated circuit architecture.”

Metal wires — like the metallic channels used to connect transistors in a computer chip — carry electricity from device to device and interconnect the semiconducting elements within transistors, the building blocks of computers.

The UC Berkeley group has been working for several years on how to make semiconductors and insulators from graphene nanoribbons, which are narrow, one-dimensional strips of atom-thick graphene, a structure composed entirely of carbon atoms arranged in an interconnected hexagonal pattern resembling chicken wire.

The new carbon-based metal is also a graphene nanoribbon, but designed with an eye toward conducting electrons between semiconducting nanoribbons in all-carbon transistors. The metallic nanoribbons were built by assembling them from smaller identical building blocks: a bottom-up approach, said Fischer’s colleague, Michael Crommie, a UC Berkeley professor of physics. Each building block contributes an electron that can flow freely along the nanoribbon.

While other carbon-based materials — like extended 2D sheets of graphene and carbon nanotubes — can be metallic, they have their problems. Reshaping a 2D sheet of graphene into nanometer scale strips, for example, spontaneously turns them into semiconductors, or even insulators. Carbon nanotubes, which are excellent conductors, cannot be prepared with the same precision and reproducibility in large quantities as nanoribbons.

“Nanoribbons allow us to chemically access a wide range of structures using bottom-up fabrication, something not yet possible with nanotubes,” Crommie said. “This has allowed us to basically stitch electrons together to create a metallic nanoribbon, something not done before. This is one of the grand challenges in the area of graphene nanoribbon technology and why we are so excited about it.”

Metallic graphene nanoribbons — which feature a wide, partially-filled electronic band characteristic of metals — should be comparable in conductance to 2D graphene itself.

“We think that the metallic wires are really a breakthrough; it is the first time that we can intentionally create an ultra-narrow metallic conductor — a good, intrinsic conductor — out of carbon-based materials, without the need for external doping,” Fischer added.

Crommie, Fischer and their colleagues at UC Berkeley and Lawrence Berkeley National Laboratory (Berkeley Lab) will publish their findings in the Sept. 25 issue of the journal Science.

Tweaking the topology

Silicon-based integrated circuits have powered computers for decades with ever increasing speed and performance, per Moore’s Law, but they are reaching their speed limit — that is, how fast they can switch between zeros and ones. It’s also becoming harder to reduce power consumption; computers already use a substantial fraction of the world’s energy production. Carbon-based computers could potentially switch many times times faster than silicon computers and use only fractions of the power, Fischer said.

Graphene, which is pure carbon, is a leading contender for these next-generation, carbon-based computers. Narrow strips of graphene are primarily semiconductors, however, and the challenge has been to make them also work as insulators and metals — opposite extremes, totally nonconducting and fully conducting, respectively — so as to construct transistors and processors entirely from carbon.

Several years ago, Fischer and Crommie teamed up with theoretical materials scientist Steven Louie, a UC Berkeley professor of physics, to discover new ways of connecting small lengths of nanoribbon to reliably create the full gamut of conducting properties.

Two years ago, the team demonstrated that by connecting short segments of nanoribbon in the right way, electrons in each segment could be arranged to create a new topological state — a special quantum wave function — leading to tunable semiconducting properties.

In the new work, they use a similar technique to stitch together short segments of nanoribbons to create a conducting metal wire tens of nanometers long and barely a nanometer wide.

The nanoribbons were created chemically and imaged on very flat surfaces using a scanning tunneling microscope. Simple heat was used to induce the molecules to chemically react and join together in just the right way. Fischer compares the assembly of daisy-chained building blocks to a set of Legos, but Legos designed to fit at the atomic scale.

“They are all precisely engineered so that there is only one way they can fit together. It’s as if you take a bag of Legos, and you shake it, and out comes a fully assembled car,” he said. “That is the magic of controlling the self-assembly with chemistry.”

Once assembled, the new nanoribbon’s electronic state was a metal — just as Louie predicted — with each segment contributing a single conducting electron.

The final breakthrough can be attributed to a minute change in the nanoribbon structure.

“Using chemistry, we created a tiny change, a change in just one chemical bond per about every 100 atoms, but which increased the metallicity of the nanoribbon by a factor of 20, and that is important, from a practical point of view, to make this a good metal,” Crommie said.

The two researchers are working with electrical engineers at UC Berkeley to assemble their toolbox of semiconducting, insulating and metallic graphene nanoribbons into working transistors.

“I believe this technology will revolutionize how we build integrated circuits in the future,” Fischer said. “It should take us a big step up from the best performance that can be expected from silicon right now. We now have a path to access faster switching speeds at much lower power consumption. That is what is driving the push toward a carbon-based electronics semiconductor industry in the future.”

Co-lead authors of the paper are Daniel Rizzo and Jingwei Jiang from UC Berkeley’s Department of Physics and Gregory Veber from the Department of Chemistry. Other co-authors are Steven Louie, Ryan McCurdy, Ting Cao, Christopher Bronner and Ting Chen of UC Berkeley. Jiang, Cao, Louie, Fischer and Crommie are affiliated with Berkeley Lab, while Fischer and Crommie are members of the Kavli Energy NanoSciences Institute.

The research was supported by the Office of Naval Research, the Department of Energy, the Center for Energy Efficient Electronics Science and the National Science Foundation.

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A U.S. Department of Energy National Laboratory Operated by the University of California.

From UC Berkeley: “Can ripples on the sun help predict solar flares?”

September 21, 2020
Robert Sanders
rlsanders@berkeley.edu

An X-class solar flare (X9.3) emitted on September 6, 2017, and captured by NASA’s Solar Dynamics Observatory in extreme ultraviolet light. (Image courtesy of NASA/GSFC/SDO.)

Solar flares are violent explosions on the sun that fling out high-energy charged particles, sometimes toward Earth, where they disrupt communications and endanger satellites and astronauts.

But as scientists discovered in 1996, flares can also create seismic activity — sunquakes — releasing impulsive acoustic waves that penetrate deep into the sun’s interior.

While the relationship between solar flares and sunquakes is still a mystery, new findings suggest that these “acoustic transients” — and the surface ripples they generate — can tell us a lot about flares and may someday help us forecast their size and severity.

A team of physicists from the United States, Colombia and Australia has found that part of the acoustic energy released from a flare in 2011 emanated from about 1,000 kilometers beneath the solar surface — the photosphere — and, thus, far beneath the solar flare that triggered the quake.

The results, reported today in The Astrophysical Journal Letters, come from a diagnostic technique called helioseismic holography, introduced in the late 1900s by French scientist Franoise Roddier and extensively developed by U.S. scientists Charles Lindsey and Douglas Braun, now at NorthWest Research Associates in Boulder, Colorado, and co-authors of the paper.

Helioseismic holography allows scientists to analyze acoustic waves triggered by flares to probe their sources, much as seismic waves from megaquakes on Earth allow seismologists to locate their epicenters. The technique was first applied to acoustic transients released from flares by a graduate student in Romania, Alina-Catalina Donea, under the supervision of Lindsey and Braun. Donea is now at Monash University in Melbourne, Australia.

NASA’s Solar Dynamics Observatory captured this image of a medium-class (M8.1) solar flare (bright area at right) on September 8, 2017. The image blends two different wavelengths of extreme ultraviolet light. (Image courtesy of NASA/GSFC/SDO.)

“It‘s the first helioseismic diagnostic specifically designed to directly discriminate the depths of the sources it reconstructs, as well as their horizontal locations,” Braun said.

“We can’t see the sun’s inside directly. It is opaque to the photons that show us the sun’s outer atmosphere, from where they can escape to reach our telescopes,” said co-author Juan Camilo Buitrago-Casas, a University of California, Berkeley, doctoral student in physics from Colombia. “The way we can know what happens inside of the sun is via seismic waves that make ripples on the solar surface similar to those caused by earthquakes on our planet. A big explosion, such as a flare, can inject a powerful acoustic pulse into the sun, whose subsequent signature we can use to map its source in some detail. The big message of this paper is that the source of at least some of this noise is deeply submerged. We are reporting the deepest source of acoustic waves so far known in the sun.”

How sunquakes produce ripples on the sun’s surface

Solar flares trigger acoustic waves (sunquakes) that travel downward but, because of increasing temperatures, are bent or refracted back to the surface, where they produce ripples that can be seen from Earth-orbiting observatories. Solar physicists have discovered a sunquake generated by an impulsive explosion 1,000 kilometers below the flare (top), suggesting that the link between sunquakes and flares is not simple. (UC Berkeley cartoon by Juan Camilo Buitrago-Casas.)

“The ripples, then, are not just a surface phenomenon, but the surface signature of waves that have gone deep beneath the active region and then back up to the outlying surface in the succeeding hour,” Lindsey said. Analyzing the surface ripples can pinpoint the source of the explosion.

“It has been widely supposed that the waves released by acoustically active flares are injected into the solar interior from above. What we are finding is the strong indication that some of the source is far beneath the photosphere,” said Juan Carlos Martínez Oliveros, a solar physics researcher at UC Berkeley’s Space Sciences Laboratory and a native of Colombia. “It seems like the flares are the precursor, or trigger, to the acoustic transient released. There is something else happening inside the sun that is generating at least some part of the seismic waves.”

“Using an analogy from medicine, what we (solar physicists) were doing before is like using X-rays to look at one snapshot of the interior of the sun. Now, we are trying to do a CAT scan, to view the solar interior in three dimensions,” added Martínez Oliveros.

The Colombians, including students Ángel Martínez and Valeria Quintero Ortega at Universidad Nacional de Colombia, in Bogotá, are co-authors of the ApJ Letters paper with their supervisor, Benjamín Calvo-Mozo, associate professor of astronomy.

“We have known about acoustic waves from flares for a little over 20 years now, and we have been imaging their sources horizontally since that time. But we have only recently discovered that some of those sources are submerged below the solar surface,” said Lindsey. “This may help explain a great mystery: Some of these acoustic waves have emanated from locations that are devoid of local surface disturbances that we can directly see in electromagnetic radiation. We have wondered for a long time how this can happen.”

A seismically active sun

For more than 50 years, astronomers have known that the sun reverberates with seismic waves, much like the Earth and its steady hum of seismic activity. This activity, which can be detected by the Doppler shift of light emanating from the surface, is understood to be driven by convective storms that form a patchwork of granules about the size of Texas, covering the sun’s surface and continually rumbling.

July 30, 2011 Sunquake – surface ripplesDr. Credit: Juan Carlos Martínez Oliveros PhD.
Time-lapse sequence of the July 30, 2011, solar flare observed by NASA’s SolarDynamics Observatory. The left frame shows visible light emissions in amber and excess extreme ultraviolet emissions in red. The right frame shows the line-of-sight Doppler velocity of the solar surface emissions. Between 20 to 40 minutes following the impulsive phase of the flare (IP on timeline), a strong acoustic disturbance released downward into the underlying solar interior has refracted back to the outlying surface, tens of thousands of kilometers from the site of the flare, to elicit outwardly propagating surface ripples (right frame). The movie is 200 times faster than real time; the ripples are amplified by a factor of three in the right frame compared to the left. (Video courtesy of Charles Lindsey.)

Amid this background noise, magnetic regions can set off violent explosions releasing waves that make the spectacular ripples that then appear on the sun’s surface in the succeeding hour, as discovered 24 years ago by astronomers Valentina Zharkova and Alexander Kosovichev.

As more sunquakes have been discovered, flare seismology has blossomed, as have the techniques to explore their mechanics and their possible relationship to the architecture of magnetic flux underlying active regions.

Among the open questions: Which flares do and don’t produce sunquakes? Can sunquakes occur without a flare? Why do sunquakes emanate primarily from the edges of sunspots, or penumbrae? Do the weakest flares produce quakes? What is the lower limit?

Until now, most solar flares have been studied as one-offs, since strong flares, even during times of maximum solar activity, may occur only a few times a year. The initial focus was on the largest, or X-class, flares, classified by the intensity of the soft X-rays they emit. Buitrago-Casas, who obtained his bachelor’s and master’s degrees from Universidad Nacional de Colombia, teamed up with Lindsey and Martínez Oliveros to conduct a systematic survey of relatively weak solar flares to increase their database, for a better understanding of the mechanics of sunquakes.

Of the 75 flares captured between 2010 and 2015 by the RHESSI satellite — a NASA X-ray satellite designed, built and operated by the Space Sciences Laboratory and retired in 2018 — 18 produced sunquakes.

Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI, originally High Energy Solar Spectroscopic Imager or HESSI) was a NASA solar flare observatory. It was the sixth mission in the Small Explorer program, selected in October 1997 and launched on 5 February 2002. Its primary mission was to explore the physics of particle acceleration and energy release in solar flares.

One of Buitrago-Casas’s acoustic transients, the one released by the flare of July 30, 2011, caught the eyes of undergraduate students Martínez, now a graduate student, and Quintero Ortega.

“We gave our student collaborators at the National University the list of flares from our survey. They were the first ones who said, ‘Look at this one. It’s different! What happened here?’” Buitrago-Casas said. “And so, we found out. It was super exciting!”

Martínez and Quintero Ortega are the first authors on a paper describing the extreme impulsivity of the waves released by that flare of July 30, 2011, that appeared in the May 20, 2020, issue of The Astrophysical Journal Letters. These waves had spectral components that gave the researchers unprecedented spatial resolution of their source distributions.

Thanks to superb data from NASA’s Solar Dynamics Observatory satellite, the team was able to pinpoint the source of the explosion that generated the seismic waves 1,000 kilometers below the photosphere. This is shallow, relative to the sun’s radius of nearly 700,000 kilometers, but deeper than any previously known acoustic source in the sun.

A source submerged below the sun’s photosphere with its own morphology and no conspicuous directly overlying disturbance in the outer atmosphere suggests that the mechanism that drives the acoustic transient is itself submerged.

“It may work by triggering a compact explosion with its own energy source, like a remotely triggered earthquake,” Lindsey said. “The flare above shakes something beneath the surface, and then a very compact unit of submerged energy gets released as acoustic sound,” he said. “There is no doubt that the flare is involved, it’s just that the existence of this deep compact source suggests the possibility of a separate, distinctive, compact, submerged energy source driving the emission.”

About half of the medium-sized solar flares that Buitrago-Casas and Martínez Oliveros have catalogued have been associated with sunquakes, showing that they commonly occur together. The team has since found other submerged sources associated with even weaker flares.

The discovery of submerged acoustic sources opens the question of whether there are instances of acoustic transients being released spontaneously, with no surface disturbance, or no flare, at all.

“If sunquakes can be generated spontaneously in the sun, this might lead us to a forecasting tool, if the transient can come from magnetic flux that has yet to break the sun’s surface,” Martínez Oliveros said. “We could then anticipate the inevitable subsequent emergence of that magnetic flux. We may even forecast some details about how large an active region is about to appear and what type — even, possibly, what kinds of flares — it might produce. This is a long shot, but well worth looking into.”

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From UC Berkeley and Los Alamos National Laboratory via phys.org: “The Hall effect links superconductivity and quantum criticality in a strange metal”

Los Alamos National Laboratory

and

via

phys.org

September 14, 2020
Ingrid Fadelli

The amplitude of the strange metal contribution in the Hall effect as a function of composition x and temperature T, estimated from the field dependence of R_H. The white dotted line is a guide to the eye, emphasizing the boundary of the region where the strange metal R_H is independent of x. Above the line the strange metal Hall depends only on temperature and independent of composition x, below the line these contributions persist to zero temperature, suggesting a direct connection to the superconducting ground state. Credit: Nature Physics (2020). Hayes et al.

Over the past few decades, researchers have identified a number of superconducting materials with atypical properties, known as unconventional superconductors. Many of these superconductors share the same anomalous charge transport properties and are thus collectively characterized as “strange metals.”

Researchers at the University of California, Berkeley (UC Berkeley) and Los Alamos National Laboratory have been investigating the anomalous transport properties of strange metals, along with several other teams worldwide. In a recent paper published in Nature Physics, they showed that in one of these materials, BaFe2(As1−xPx)2, superconductivity and quantum criticality are linked by what is known as the Hall effect.

For decades, physicists have been unable to fully understand T-linear resistivity, a signature of strange metals that has often been observed in many unconventional superconductors. In 2016, the team at UC Berkeley and Los Alamos National Lab observed an unusual scaling relationship between the magnetic field and temperature in superconductor BaFe2(As1−xPx)2 [Nature Physics].

Scaling phenomena are typically observed just before a system transitions from one phase to another (e.g. from liquid to gas), moments called critical points. This inspired the researchers to investigate whether a similar phenomenon also occurred in the Hall effect, a related charge transport phenomenon.

“The scaling behavior arises because near a critical point, some properties become scale invariant,” James G. Analytis, one of the researchers who carried out the study, told Phys.org. “This is because there are phase fluctuations at the critical point that occur at all length and time scales. The same basic phenomenon leads to critical opalescence in a liquid-gas transition, but in the present case, the fluctuations have their origin in the Heisenberg uncertainty principle. In our recent study, we did not observe the scaling behavior as clearly as we did before, but we found something we did not expect.”

To conduct their experiments, Analytis and their colleagues synthesized BaFe2(As1−xPx)2 crystals at the Lawrence Berkeley National Laboratory (LBNL) and then placed them under high magnetic fields at Los Alamos National Lab’s high field facility, which is managed by the NSF-funded National High Magnetic Field Lab (NHMFL). At this field facility, researchers can collect measurements for a significant amount of magnet time.

“It is highly competitive to get this magnet time, which allows you to measure up to 65 T,” Analytis explained. “Each material needs to be measured separately, with multiple samples to ensure reproducibility. In all, we probably spent about four weeks of magnet time to gather our data.”

The experiments carried out by Analytis and his colleagues yielded a number of interesting results. First, the researchers found that the Hall effect appears to be composed of two different ‘terms’: a conventional one that is simply related to the number of electrons in the system, and a strange-metal term that peaks when BaFe2(As1−xPx)2 is approaching its quantum critical point.

“Separating the Hall effect into two contributions is quite natural in ferromagnetic metals because the system has two clear contributions; the carriers in the metal and the magnetically ordered spins,” Analytis explained. “The second contribution is called the anomalous Hall effect. What we see appears to be analogous to an anomalous Hall effect, but I emphasize that there is no ferromagnetism. Here, the anomalous contribution appears to arise from magnetic fluctuations near the critical point.”

Two key facts illustrate the link between quantum criticality and superconductivity unveiled by Analytis and his colleagues: The first is that in strange metals, superconductivity occurs in a whole phase diagram; the second is that the Hall effect is essentially a measure of the number of particles (i.e., electrons or holes) in a system.

The researchers observed that the anomalous effect observed in BaFe2(As1−xPx)2 as it approaches its quantum critical point only ceases when superconductivity does. Moreover, they found that the zero-temperature magnitude of the Hall effect’s anomalous term were correlated to the magnitude of the superconducting Tc. This suggests that the strange metal’s contribution to the Hall effect is, in fact, a measure of the emergent entities that are responsible for superconductivity.

“There was a second observation connected to the scale invariance observed before,” Analytis said. “In a region of the phase diagram known as the ‘critical fan’ (the region thought to be dominated by fluctuations), the strange metal contribution depends only on the temperature, as if temperature sets the scale of the fluctuations in the system. Most importantly, the strange metal contribution was independent of composition X, even though the conventional contribution changed by a factor of three or more; which means that the strange metal Hall effect is not simply an additional source of charge, but that it arises from the collective motion of all the electrons as they approach a quantum critical phase transition.”

When studying high Tc, researchers typically try to understand the emergent excitations that are responsible for superconductivity in a material. In conventional superconductors, these excitations are now known to be characterized as simple electrons or holes.

The recent study by Analytis and his colleagues could ultimately illuminate the nature of the excitations responsible for superconductivity in strange metals, which has so far remained elusive. Moreover, the researchers have identified a strategy that can be used to measure whether these excitations are present in a material or not.

“It would be very exciting to see whether the properties we unveiled extend to other superconductors,” Analytis said. “Right now, we would like to extend these measurements to different parts of the phase diagram and to different compounds. These are all long and complicated experiments requiring extensive synthesis and time in high field labs (like the NHMFL), but at least we know exactly what we are looking for, now.”

In their next studies, the researchers would also like to start looking for strategies and tools that could be used to probe the spin degrees of freedom in unconventional superconductors directly. In fact, most existing methods tend to examine a material’s charge degrees of freedom, which considerably limits their generalizability across different materials.

“The Hall effect will always mix these up, and we got lucky that in these materials, they separate into ‘conventional’ and ‘strange metal’ contributions,” Analytis said. “But in order to see universalities across different materials classes, it will be important to develop new probes with more direct sensitivity to the ‘strange metal’ part of the system.”

See the full article here .

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Los Alamos National Laboratory’s mission is to solve national security challenges through scientific excellence.

Los Alamos National Laboratory, a multidisciplinary research institution engaged in strategic science on behalf of national security, is operated by Los Alamos National Security, LLC, a team composed of Bechtel National, the University of California, The Babcock & Wilcox Company, and URS for the Department of Energy’s National Nuclear Security Administration.
Los Alamos enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health, and global security concerns.

Operated by Los Alamos National Security, LLC for the U.S. Dept. of Energy’s NNSA

From UC Berkeley: “Breakthrough Listen scans Milky Way Galaxy for beacons of civilization”

Breakthrough Listen Project

Artist’s concept of a nearby civilization signaling Earth after observing our planet crossing in front of the sun. Astronomers have now scanned 20 nearby stars in the Earth transit zone in search of such signals. (UC Berkeley image courtesy of Breakthrough Listen).

The Breakthrough Listen Initiative today (Friday, Feb. 14) released data from the most comprehensive survey yet of radio emissions from the plane of the Milky Way Galaxy and the region around its central black hole, and it is inviting the public to search the data for signals from intelligent civilizations.

UC Observatories Lick Autmated Planet Finder, fully robotic 2.4-meter optical telescope at Lick Observatory, situated on the summit of Mount Hamilton, east of San Jose, California, USA

GBO radio telescope, Green Bank, West Virginia, USA

CSIRO/Parkes Observatory, located 20 kilometres north of the town of Parkes, New South Wales, Australia

SKA Meerkat telescope, 90 km outside the small Northern Cape town of Carnarvon, SA

Newly added

CfA/VERITAS, a major ground-based gamma-ray observatory with an array of four Čerenkov Telescopes for gamma-ray astronomy in the GeV – TeV energy range. Located at Fred Lawrence Whipple Observatory,Mount Hopkins, Arizona, US in AZ, USA, Altitude 2,606 m (8,550 ft)

At a media briefing today in Seattle as part of the annual meeting of the American Association for the Advancement of Science (AAAS), Breakthrough Listen principal investigator Andrew Siemion of the University of California, Berkeley, announced the release of nearly 2 petabytes of data, the second data dump from the four-year old search for extraterrestrial intelligence (SETI). A petabyte of radio and optical telescope data was released last June, the largest release of SETI data in the history of the field.

The data, most of it fresh from the telescope prior to detailed study from astronomers, comes from a survey of the radio spectrum between 1 and 12 gigahertz (GHz). About half of the data comes via the Parkes radio telescope in New South Wales, Australia, which, because of its location in the Southern Hemisphere, is perfectly situated and instrumented to scan the entire galactic disk and galactic center. The telescope is part of the Australia Telescope National Facility, owned and managed by the country’s national science agency, CSIRO.

The remainder of the data was recorded by the Green Bank Observatory in West Virginia, the world’s largest steerable radio dish, and an optical telescope called the Automated Planet Finder, built and operated by UC Berkeley and located at Lick Observatory outside San Jose, California.

“Since Breakthrough Listen’s initial data release last year, we have doubled what is available to the public,” said Breakthrough Listen’s lead system administrator, Matt Lebofsky. “It is our hope that these data sets will reveal something new and interesting, be it other intelligent life in the universe or an as-yet-undiscovered natural astronomical phenomenon.”

“For the whole of human history, we had a limited amount of data to search for life beyond Earth. So, all we could do was speculate. Now, as we are getting a lot of data, we can do real science and, with making this data available to general public, so can anyone who wants to know the answer to this deep question,” said Yuri Milner, the founder of Breakthrough Listen.

NRAO/Karl V Jansky Expanded Very Large Array, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

The VLA is teaming up with the SETI Institute to capture data that can be searched for intelligent signals.

The National Radio Astronomy Observatory (NRAO) and the privately-funded SETI Institute in Mountain View, California, also announced today an agreement to collaborate on new systems to add SETI capabilities to radio telescopes operated by NRAO. The first project will develop a system to piggyback on the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) in New Mexico and provide data to state-of-the-art digital backend equipment built by the SETI Institute.

“The SETI Institute will develop and install an interface on the VLA, permitting unprecedented access to the rich data stream continuously produced by the telescope as it scans the sky,“ said Siemion, who, in addition to his UC Berkeley position, is the Bernard M. Oliver Chair for SETI at the SETI Institute. “This interface will allow us to conduct a powerful, wide-area SETI survey that will be vastly more complete than any previous such search.”

“As the VLA conducts its usual scientific observations, this new system will allow for an additional and important use for the data we’re already collecting,” said NRAO Director Tony Beasley. “Determining whether we are alone in the universe as technologically capable life is among the most compelling questions in science, and NRAO telescopes can play a major role in answering it.”

Earth transit zone survey

In releasing the new radio and optical data, Siemion highlighted a new analysis of a small subset of the data: radio emissions from 20 nearby stars that are aligned with the plane of Earth’s orbit such that an advanced civilization around those stars could see Earth pass in front of the sun (a “transit” like those focused on by NASA’s Kepler space telescope). Conducted by the Green Bank Telescope, the Earth transit zone survey observed in the radio frequency range between 4 and 8 gigahertz, the so-called C-band. The data were then analyzed by former UC Berkeley undergraduate Sofia Sheikh, now a graduate student at Pennsylvania State University, who looked for bright emissions at a single radio wavelength or a narrow band around a single wavelength. She has submitted the paper to The Astrophysical Journal.

“This is a unique geometry,” Sheikh said. “It is how we discovered other exoplanets, so it kind of makes sense to extrapolate and say that that might be how other intelligent species find planets, as well. This region has been talked about before, but there has never been a targeted search of that region of the sky.”

While Sheikh and her team found no technosignatures of civilization, the analysis and other detailed studies the Breakthrough Listen group has conducted are gradually putting limits on the location and capabilities of advanced civilizations that may exist in our galaxy.

“We didn’t find any aliens, but we are setting very rigorous limits on the presence of a technologically capable species, with data for the first time in the part of the radio spectrum between 4 and 8 gigahertz,” Siemion said. “These results put another rung on the ladder for the next person who comes along and wants to improve on the experiment.”

Sheikh noted that her mentor, Jason Wright at Penn State, estimated that if the world’s oceans represented every place and wavelength we could search for intelligent signals, we have, to date, explored only a hot tub’s worth of it.

“My search was sensitive enough to see a transmitter basically the same as the strongest transmitters we have on Earth, because I looked at nearby targets on purpose,” Sheikh said. “So, we know that there isn’t anything as strong as our Arecibo telescope beaming something at us. Even though this is a very small project, we are starting to get at new frequencies and new areas of the sky.”
Beacons in the galactic center?

The so-far unanalyzed observations from the galactic disk and galactic center survey were a priority for Breakthrough Listen because of the higher likelihood of observing an artificial signal from that region of dense stars. If artificial transmitters are not common in the galaxy, then searching for a strong transmitter among the billions of stars in the disk of our galaxy is the best strategy, Simeon said.

Breakthrough Listen, based at UC Berkeley, collects petabytes of data from the Green Bank Telescope in West Virginia (right) and the Parkes radio telescope in Australia (left) and makes it available to the science community to analyze in search of signals from intelligent civilizations. (Graphic courtesy of Breakthrough Listen)

On the other hand, putting a powerful, intergalactic transmitter in the core of our galaxy, perhaps powered by the 4 million-solar-mass black hole there, might not be beyond the capabilities of a very advanced civilization. Galactic centers may be so-called Schelling points: likely places for civilizations to meet up or place beacons, given that they cannot communicate among themselves to agree on a location.

“The galactic center is the subject of a very specific and concerted campaign with all of our facilities because we are in unanimous agreement that that region is the most interesting part of the Milky Way galaxy,” Siemion said. “If an advanced civilization anywhere in the Milky Way wanted to put a beacon somewhere, getting back to the Schelling point idea, the galactic center would be a good place to do it. It is extraordinarily energetic, so one could imagine that if an advanced civilization wanted to harness a lot of energy, they might somehow use the supermassive black hole that is at the center of the Milky Way galaxy.”

Visit from an interstellar comet

Breakthrough Listen also released observations of the interstellar comet 2I/Borisov, which had a close encounter with the sun in December and is now on its way out of the solar system. The group had earlier scanned the interstellar rock ‘Oumuamua, which passed through the center of our solar system in 2017. Neither exhibited technosignatures.

NASA’s Hubble Space Telescope took this photo of the interstellar comet 2I/Borisov in October 2019, two months before its closest approach to the sun. (Photo courtesy of NASA, ESA and D. Jewitt, UCLA))

“If interstellar travel is possible, which we don’t know, and if other civilizations are out there, which we don’t know, and if they are motivated to build an interstellar probe, then some fraction greater than zero of the objects that are out there are artificial interstellar devices,” said Steve Croft, a research astronomer with the Berkeley SETI Research Center and Breakthrough Listen. “Just as we do with our measurements of transmitters on extrasolar planets, we want to put a limit on what that number is.”

Regardless of the kind of SETI search, Siemion said, Breakthrough Listen looks for electromagnetic radiation that is consistent with a signal that we know technology produces, or some anticipated signal that technology could produce, and inconsistent with the background noise from natural astrophysical events. This also requires eliminating signals from cellphones, satellites, GPS, internet, Wi-fi and myriad other human sources.

In Sheikh’s case, she turned the Green Bank telescope on each star for five minutes, pointed away for another five minutes and repeated that twice more. She then threw out any signal that didn’t disappear when the telescope pointed away from the star. Ultimately, she whittled an initial 1 million radio spikes down to a couple hundred, which she was able to eliminate as Earth-based human interference. The last four unexplained signals turned out to be from passing satellites.

Siemion emphasized that the Breakthrough Listen team intends to analyze all the data released to date and to do it systematically and often.

“Of all the observations we have done, probably 20% or 30% have been included in a data analysis paper,” Siemion said. “Our goal is not just to analyze it 100%, but 1000% or 2000%. We want to analyze it iteratively.”

Breakthrough Listen, based at UC Berkeley, is supported by a $100 million, 10-year commitment from the Breakthrough Initiatives, founded in 2015 by Yuri and Julia Milner to explore the universe, seek scientific evidence of life beyond Earth and encourage public debate from a planetary perspective.

RELATED INFORMATION

Data Release 2 portal
SETI Institute and National Radio Astronomy Observatory Team Up for SETI Science at the Very Large Array (SETI Institute press release)
New Technologies, Strategies Expanding Search for Extraterrestrial Life (NRAO press release)
Berkeley SETI Research Center
Breakthrough Initiatives
Sofia Sheikh’s website

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From UC Berkeley: “Blue diode illustrates limitations, promise of perovskite semiconductors”

January 24, 2020
Robert Sanders
rlsanders@berkeley.edu

UC Berkeley chemists created a type of halide perovskite crystal that emits blue light, something that has been hard to achieve with the trendy new material. But the researchers also found that these materials are inherently unstable, requiring careful control of temperature and chemical environment to maintain their precise color. (UC Berkeley photo courtesy of Peidong Yang)

University of California, Berkeley, scientists have created a blue light-emitting diode (LED) from a trendy new semiconductor material, halide perovskite, overcoming a major barrier to employing these cheap, easy-to-make materials in electronic devices.

In the process, however, the researchers discovered a fundamental property of halide perovskites that may prove a barrier to their widespread use as solar cells and transistors.

Alternatively, this unique property may open up a whole new world for perovskites far beyond that of today’s standard semiconductors.

In a paper appearing Jan. 24 in the journal Science Advances, UC Berkeley chemist Peidong Yang and his colleagues show that the crystal structure of the halide perovskites changes with temperature, humidity and the chemical environment, disrupting their optical and electronic properties. Without close control of the physical and chemical environment, perovskite devices are inherently unstable. This is not a major problem for traditional semiconductors.

“Some people may say this is a limitation. For me, this is a great opportunity,” said Yang, the S. K. and Angela Chan Distinguished Chair in Energy in the College of Chemistry and director of the Kavli Energy NanoSciences Institute. “This is new physics: a new class of semiconductors that can be readily reconfigured, depending on what sort of environment you put them in. They could be a really good sensor, maybe a really good photoconductor, because they will be very sensitive in their response to light and chemicals.”

Current semiconductors made of silicon or gallium nitride are very stable over a range of temperatures, primarily because their crystal structures are held together by strong covalent bonds. Halide perovskite crystals are held together by weaker ionic bonds, like those in a salt crystal. This means they’re easier to make — they can be evaporated out of a simple solution — but also susceptible to humidity, heat and other environmental conditions.

“This paper is not just about showing off that we made this blue LED,” said Yang, who is a senior faculty scientist at Lawrence Berkeley National Laboratory (Berkeley Lab) and a UC Berkeley professor of materials science and engineering. “We are also telling people that we really need to pay attention to the structural evolution of perovskites during the device operation, any time you drive these perovskites with an electrical current, whether it is an LED, a solar cell or a transistor. This is an intrinsic property of this new class of semiconductor and affects any potential optoelectronic device in the future using this class of material.”

The blue diode blues

Making semiconductor diodes that emit blue light has always been a challenge, Yang said. The 2014 Nobel Prize for Physics was awarded for the breakthrough creation of efficient blue light-emitting diodes from gallium nitride. Diodes, which emit light when an electric current flows through them, are optoelectronic components in fiber optic circuits as well as general purpose LED lights.

The crystal structure of the blue-emitting halide perovskite changes with heating from room temperature, 300 Kelvin, to 450 Kelvin, the typical operating temperature of an electronic device. The structural change alters the wavelength of light, changing it from blue to blue-green, an unacceptable instability in electronics. (UC Berkeley photo courtesy of Peidong Yang)

Since halide perovskites first drew wide attention in 2009, when Japanese scientists discovered that they make highly efficient solar cells, these easily made, inexpensive crystals have excited researchers. So far, red- and green-emitting diodes have been demonstrated, but not blue. Halide perovskite blue-emitting diodes have been unstable — that is, their color shifts to longer, redder wavelengths with use.

As Yang and his colleagues discovered, this is due to the unique nature of perovskites’ crystal structure. Halide perovskites are composed of a metal, such as lead or tin, equal numbers of larger atoms, such as cesium, and three times the number of halide atoms, such as chlorine, bromine or iodine.

When these elements are mixed together in solution and then dried, the atoms assemble into a crystal, just as salt crystalizes from sea water. Using a new technique and the ingredients cesium, lead and bromine, the UC Berkeley and Berkeley Lab chemists created perovskite crystals that emit blue light and then bombarded them with X-rays at the Stanford Linear Accelerator Center (SLAC) to determine their crystalline structure at various temperatures. They found that, when heated from room temperature (about 300 Kelvin) to around 450 Kelvin, a common operating temperature for semiconductors, the crystal’s squashed structure expanded and eventually sprang into a new orthorhombic or tetragonal configuration.

Since the light emitted by these crystals depends on the arrangement of and distances between atoms, the color changed with temperature, as well. A perovskite crystal that emitted blue light (450 nanometers wavelength) at 300 Kelvin suddenly emitted blue-green light at 450 Kelvin.

Yang attributes perovskites’ flexible crystal structure to the weaker ionic bonds typical of halide atoms. Naturally occurring mineral perovskite incorporates oxygen instead of halides, producing a very stable mineral. Silicon-based and gallium nitride semiconductors are similarly stable because the atoms are linked by strong covalent bonds.

Making blue-emitting perovskites

According to Yang, blue-emitting perovskite diodes have been hard to create because the standard technique of growing the crystals as a thin film encourages formation of mixed crystal structures, each of which emits at a different wavelength. Electrons get funneled down to those crystals with the smallest bandgap — that is, the smallest range of unallowed energies — before emitting light, which tends to be red.

Two different types of blue light-emitting perovskite crystal. On the left, perovskite with two layers of the octahedral perovskite structure produces a shorter wavelength of blue light than a crystal with three octahedral layers, right. (UC Berkeley photos courtesy of Peidong Yang)

To avoid this, Yang’s postdoctoral fellows and co-first authors — Hong Chen, Jia Lin and Joohoon Kang — grew single, layered crystals of perovskite and, adapting a low-tech method for creating graphene, used tape to peel off a single layer of uniform perovskite. When incorporated into a circuit and zapped with electricity, the perovskite glowed blue. The actual blue wavelength varied with the number of layers of octahedral perovskite crystals, which are separated from one another by a layer of organic molecules that allows easy separation of perovskite layers and also protects the surface.

Nevertheless, the SLAC experiments showed that the blue-emitting perovskites changed their emission colors with temperature. This property can have interesting applications, Yang said. Two years ago, he demonstrated a window made of halide perovskite that becomes dark in the sun and transparent when the sun goes down and also produces photovoltaic energy.

We need to think in different ways of using this class of semiconductor,” he said. “We should not put halide perovskites into the same application environment as a traditional covalent semiconductor, like silicon. We need to realize that this class of material has intrinsic structural properties that make it ready to reconfigure. We should utilize that.”

The work was supported by the U.S. Department of Energy’s Basic Energy Sciences program. Other co-authors of the paper are Qiao Kong, Dylan Lu, Minliang Lai, Li Na Quan and Jianbo Jin of UC Berkeley; Jun Kang, Zhenni Lin and Lin-wang Wang of Berkeley Lab; and Michael Toney of SLAC. Chen is currently at Southern University of Science and Technology in Shenzhen, China; Lin is at Shanghai University of Electric Power; and Joohoon Kang is at Sungkyunkwan University in Seoul, South Korea.

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