JPL News: Black Hole Has Major Flare

The baffling and strange behaviors of black holes have become somewhat less mysterious recently, with new observations from NASA's Explorer missions Swift and the Nuclear Spectroscopic Telescope Array, or NuSTAR. The two space telescopes caught a supermassive black hole in the midst of a giant eruption of X-ray light, helping astronomers address an ongoing puzzle: How do supermassive black holes flare?

Read more at JPL News

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Two space telescopes have caught a supermassive black hole in the midst of a giant eruption of X-ray light.

Caltech Physicists Uncover Novel Phase of Matter

Finding could have implications for high-temperature superconductivity

A team of physicists led by Caltech's David Hsieh has discovered an unusual form of matter—not a conventional metal, insulator, or magnet, for example, but something entirely different. This phase, characterized by an unusual ordering of electrons, offers possibilities for new electronic device functionalities and could hold the solution to a long-standing mystery in condensed matter physics having to do with high-temperature superconductivity—the ability for some materials to conduct electricity without resistance, even at "high" temperatures approaching  –100 degrees Celsius.

"The discovery of this phase was completely unexpected and not based on any prior theoretical prediction," says Hsieh, an assistant professor of physics, who previously was on a team that discovered another form of matter called a topological insulator. "The whole field of electronic materials is driven by the discovery of new phases, which provide the playgrounds in which to search for new macroscopic physical properties."

Hsieh and his colleagues describe their findings in the November issue of Nature Physics, and the paper is now available online. Liuyan Zhao, a postdoctoral scholar in Hsieh's group, is lead author on the paper.

The physicists made the discovery while testing a laser-based measurement technique that they recently developed to look for what is called multipolar order. To understand multipolar order, first consider a crystal with electrons moving around throughout its interior. Under certain conditions, it can be energetically favorable for these electrical charges to pile up in a regular, repeating fashion inside the crystal, forming what is called a charge-ordered phase. The building block of this type of order, namely charge, is simply a scalar quantity—that is, it can be described by just a numerical value, or magnitude.

In addition to charge, electrons also have a degree of freedom known as spin. When spins line up parallel to each other (in a crystal, for example), they form a ferromagnet—the type of magnet you might use on your refrigerator and that is used in the strip on your credit card. Because spin has both a magnitude and a direction, a spin-ordered phase is described by a vector.

Over the last several decades, physicists have developed sophisticated techniques to look for both of these types of phases. But what if the electrons in a material are not ordered in one of those ways? In other words, what if the order were described not by a scalar or vector but by something with more dimensionality, like a matrix? This could happen, for example, if the building block of the ordered phase was a pair of oppositely pointing spins—one pointing north and one pointing south—described by what is known as a magnetic quadrupole. Such examples of multipolar-ordered phases of matter are difficult to detect using traditional experimental probes.

As it turns out, the new phase that the Hsieh group identified is precisely this type of multipolar order.  

To detect multipolar order, Hsieh's group utilized an effect called optical harmonic generation, which is exhibited by all solids but is usually extremely weak. Typically, when you look at an object illuminated by a single frequency of light, all of the light that you see reflected from the object is at that frequency. When you shine a red laser pointer at a wall, for example, your eye detects red light. However, for all materials, there is a tiny amount of light bouncing off at integer multiples of the incoming frequency. So with the red laser pointer, there will also be some blue light bouncing off of the wall. You just do not see it because it is such a small percentage of the total light. These multiples are called optical harmonics.

The Hsieh group's experiment exploited the fact that changes in the symmetry of a crystal will affect the strength of each harmonic differently. Since the emergence of multipolar ordering changes the symmetry of the crystal in a very specific way—a way that can be largely invisible to conventional probes—their idea was that the optical harmonic response of a crystal could serve as a fingerprint of multipolar order.   

"We found that light reflected at the second harmonic frequency revealed a set of symmetries completely different from those of the known crystal structure, whereas this effect was completely absent for light reflected at the fundamental frequency," says Hsieh. "This is a very clear fingerprint of a specific type of multipolar order."

The specific compound that the researchers studied was strontium-iridium oxide (Sr2IrO4), a member of the class of synthetic compounds broadly known as iridates. Over the past few years, there has been a lot of interest in Sr2IrO4 owing to certain features it shares with copper-oxide-based compounds, or cuprates. Cuprates are the only family of materials known to exhibit superconductivity at high temperatures—exceeding 100 Kelvin (–173 degrees Celsius). Structurally, iridates and cuprates are very similar. And like the cuprates, iridates are electrically insulating antiferromagnets that become increasingly metallic as electrons are added to or removed from them through a process called chemical doping. A high enough level of doping will transform cuprates into high-temperature superconductors, and as cuprates evolve from being insulators to superconductors, they first transition through a mysterious phase known as the pseudogap, where an additional amount of energy is required to strip electrons out of the material. For decades, scientists have debated the origin of the pseudogap and its relationship to superconductivity—whether it is a necessary precursor to superconductivity or a competing phase with a distinct set of symmetry properties. If that relationship were better understood, scientists believe, it might be possible to develop materials that superconduct at temperatures approaching room temperature.

Recently, a pseudogap phase also has been observed in Sr2IrO4—and Hsieh's group has found that the multipolar order they have identified exists over a doping and temperature window where the pseudogap is present. The researchers are still investigating whether the two overlap exactly, but Hsieh says the work suggests a connection between multipolar order and pseudogap phenomena.

"There is also very recent work by other groups showing signatures of superconductivity in Sr2IrO4 of the same variety as that found in cuprates," he says. "Given the highly similar phenomenology of the iridates and cuprates, perhaps iridates will help us resolve some of the longstanding debates about the relationship between the pseudogap and high-temperature superconductivity."

Hsieh says the finding emphasizes the importance of developing new tools to try to uncover new phenomena. "This was really enabled by a simultaneous technique advancement," he says.

Furthermore, he adds, these multipolar orders might exist in many more materials. "Sr2IrO4 is the first thing we looked at, so these orders could very well be lurking in other materials as well, and that's exactly what we are pursuing next."

Additional Caltech authors on the paper, "Evidence of an odd-parity hidden order in a spin–orbit coupled correlated iridate," are Darius H. Torchinsky, Hao Chu, and Vsevolod Ivanov. Ron Lifshitz of Tel Aviv University, Rebecca Flint of Iowa State University, and Tongfei Qi and Gang Cao of the University of Kentucky are also coauthors. The work was supported by funding from the Army Research Office, the National Science Foundation (NSF), and the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center with support from the Gordon and Betty Moore Foundation.

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Physicists Uncover Novel Phase of Matter
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Not a conventional metal, insulator, or magnet, it could hold the solution to a long-standing mystery related to high-temperature superconductivity.
Friday, October 30, 2015
Beckman Institute Auditorium – Beckman Institute

Teaching Statement Workshop

Feynman's Nobel Year

A Milestone in Physics

Fifty years ago on October 21, 1965, Caltech's Richard Feynman shared the Nobel Prize in Physics with Julian Schwinger and Sin-Itiro Tomonaga. The three independently brokered workable marriages between 20th-century quantum mechanics and 19th-century electromagnetic field theory.

Quantum electrodynamics, as this previously reluctant partnership is known, treats the behavior of electromagnetic fields in the same manner as it treats the behavior of the electrons producing them—as particles, whose interactions can be described using probability theory. (In this case, the particles are little packages of electromagnetic energy called photons, which we usually think of as particles of light.) The so-called probability amplitude for anything more elaborate than an isolated hydrogen atom is far too complex to solve directly, so the standard quantum-mechanics approach is to start with a solvable, relatively simple equation and keep adding smaller and smaller corrections to it according to well-defined rules. The solution gets closer and closer to the actual answer as the corrections diminish in size, so you simply decide how accurate you need to be for the task at hand. However, describing an electromagnetic field in such a manner means allowing the photons to carry infinite momentum, and it had become clear by the late 1930s that such equations did not converge on the correct answer—adding corrections merely piled infinities upon infinities.

While Schwinger and Tomonaga used highly mathematical approaches to the problem, Feynman characteristically took a different point of view. He drew pictures of every possible interaction between photons and electrons, including those involving "virtual" particles undetectable by the outside world. For example, an electron can spontaneously emit and reabsorb a photon—a self-interaction that contributes appreciably to the electron's mass. And a photon can transmute into an electron and its antimatter twin, the positron, with the two immediately annihilating each another to produce a new photon and helping to create the so-called vacuum energy that pervades empty space. Far more complex pictures are possible—and usually necessary. These iconic doodles, now called Feynman diagrams, allowed him to calculate each scenario's probability amplitude independently and add them all up to get the correct answer.

Back in the 1960s, Nobel laureates got a congratulatory 9:00 a.m. telegram from Stockholm rather than a 3:00 a.m. phone call. Even so, Feynman was awakened at 3:45 a.m. by a reporter who broke the news to him, then asked, "Aren't you pleased to hear that you've won the prize?" "I could have found out later this morning," the groggy Feynman replied. "Well, how do you feel, now that you've won it?" the reporter persisted.

At the customary press conference held at a more reasonable hour at Caltech's faculty club, the Athenaeum, a reporter asked, "Is there any way your work can be explained in layman's terms?" "There certainly must be," Feynman replied. "But I don't know what it is."

Feynman was a master teacher with a flair for showmanship, and for him to be at a loss for words—even in jest—may have been a first. The final installment of his textbook The Feynman Lectures on Physics had come out that June. Distilled from the Physics 1 and 2 course sequence he had taught to 180 Caltech freshmen in 1961–62 and to the same group as sophomores the following year, the work's three volumes appeared in 1963, 1964, and 1965. The lectures, a complete reimagining of introductory physics, had been motivated by the rapid pace of discoveries in the field in the 1950s and by the improvements in high-school mathematics instruction brought on by the space race—which the Soviets were winning in 1961 by a score of three to nothing, having successively put the first satellite, the first animal (Laika the dog), and the first human (Yuri Gagarin) into orbit.

"A substantial number" of Caltech's physics faculty had proffered outlines of topics the two-year course should cover, wrote professor Robert Leighton (BS '41, MS '44, PhD '47) in the foreword to the series. He noted that the hundred-plus lectures were envisioned as "a cooperative effort by N staff members who would share the total burden symmetrically and equally: each man would take responsibility for 1/N of the material, deliver the lectures, and write text material for his part." This unworkable scheme was quickly abandoned after physics professor Matthew Sands volunteered Feynman for the entire job. Feynman agreed—on the condition that he did not have to write anything. Instead, each lecture was audiotaped and transcribed, and every diagram was photographed. "It was expected that the necessary editing would be minor . . . to be done by one or two graduate students on a part-time basis. Unfortunately, this expectation was short-lived," Leighton wrote. In fact, it "required the close attention of a professional physicist for from ten to twenty hours per lecture!" Leighton and Sands worked on it by turn, with Feynman doing the final edit himself.

In the end, however, it was all worth the effort. More than 1.5 million sets of the iconic, bright red volumes have been sold in English alone, and at least a dozen translations into other languages exist. The book has gone through three editions and remains in print to this day; on September 13, 2013 Caltech posted a freely available electronic version whose equations and graphics scale automatically to the reader's device. In the 25 months since then, the site has been accessed more than eight million times by nearly 1.7 million individuals.

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Richard Feynman had a banner year in 1965, sharing the Nobel Prize in Physics and seeing the final volume of "The Feynman Lectures on Physics" published.

Astronomers Peer Inside Stars, Finding Giant Magnets

Astronomers have for the first time probed the magnetic fields in the mysterious inner regions of stars, finding they are strongly magnetized.

Using a technique called asteroseismology, the scientists were able to calculate the magnetic field strengths in the fusion-powered hearts of dozens of red giants, stars that are evolved versions of our sun.

"In the same way medical ultrasound uses sound waves to image the interior of the human body, asteroseismology uses sound waves generated by turbulence on the surface of stars to probe their inner properties," says Caltech postdoctoral researcher Jim Fuller, who co-led a new study detailing the research.

The findings, published in the October 23 issue of Science, will help astronomers better understand the life and death of stars. Magnetic fields likely determine the interior rotation rates of stars; such rates have dramatic effects on how the stars evolve.

Until now, astronomers have been able to study the magnetic fields of stars only on their surfaces, and have had to use supercomputer models to simulate the fields near the cores, where the nuclear-fusion process takes place. "We still don't know what the center of our own sun looks like," Fuller says.

Red giants have a different physical makeup from so-called main-sequence stars such as our sun—one that makes them ideal for asteroseismology (a field that was born at Caltech in 1962, when the late physicist and astronomer Robert Leighton discovered the solar oscillations using the solar telescopes at Mount Wilson). The cores of red-giant stars are much denser than those of younger stars. As a consequence, sound waves do not reflect off the cores, as they do in stars like our sun. Instead, the sound waves are transformed into another class of waves, called gravity waves.

"It turns out the gravity waves that we see in the red giants do propagate all the way to the center of these stars," says co-lead author Matteo Cantiello, a specialist in stellar astrophysics from UC Santa Barbara's Kavli Institute for Theoretical Physics (KITP).

This conversion from sound waves to gravity waves has major consequences for the tiny shape changes, or oscillations, that red giants undergo. "Depending on their size and internal structure, stars oscillate in different patterns," Fuller says. In one form of oscillation pattern, known as the dipole mode, one hemisphere of the star becomes brighter while the other becomes dimmer. Astronomers observe these oscillations in a star by measuring how its light varies over time.

When strong magnetic fields are present in a star's core, the fields can disrupt the propagation of gravity waves, causing some of the waves to lose energy and become trapped within the core. Fuller and his coauthors have coined the term "magnetic greenhouse effect" to describe this phenomenon because it works similarly to the greenhouse effect on Earth, in which greenhouse gases in the atmosphere help trap heat from the sun. The trapping of gravity waves inside a red giant causes some of the energy of the star's oscillation to be lost, and the result is a smaller than expected dipole mode.

In 2013, NASA's Kepler space telescope, which can measure stellar brightness variations with incredibly high precision, detected dipole-mode damping in several red giants. Dennis Stello, an astronomer at the University of Sydney, brought the Kepler data to the attention of Fuller and Cantiello. Working in collaboration with KITP director Lars Bildsten and Rafael Garcia of France's Alternative Energies and Atomic Energy Commission, the scientists showed that the magnetic greenhouse effect was the most likely explanation for dipole-mode damping in the red giants. Their calculations revealed that the internal magnetic fields of the red giants were as much as 10 million times stronger than Earth's magnetic field.

"This is exciting, as internal magnetic fields play an important role for the evolution and ultimate fate of stars," says Professor of Theoretical Astrophysics Sterl Phinney, Caltech's executive officer for astronomy, who was not involved in the study.

A better understanding of the interior magnetic fields of stars could also help settle a debate about the origin of powerful magnetic fields on the surfaces of certain neutron stars and white dwarfs, two classes of stellar corpses that form when stars die.

"The magnetic fields that they find in the red-giant cores are comparable to those of the strongly magnetized white dwarfs," Phinney says. "The fact that only some of the red giants show the dipole suppression, which indicates strong core fields, may well be related to why only some stars leave behind remnants with strong magnetic fields after they die."

The asteroseismology technique the team used to probe red giants probably will not work with our sun. "However," Fuller says, "stellar oscillations are our best probe of the interiors of stars, so more surprises are likely."

The paper is entitled "Asteroseismology can reveal strong internal magnetic fields in red giant stars." In addition to Fuller, Cantiello, Garcia, and Bildsten, the other coauthor is Dennis Stello from the University of Sydney. Jim Fuller was supported by the National Science Foundation and a Lee A. DuBridge Postdoctoral Fellowship at Caltech.

This work was written collaboratively on the web. An Open Science version of the published paper can be found on Authorea, including a layperson's summary.

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Hitlin Awarded Prestigious Prize for Particle Physics

Professor of Physics David Hitlin has been awarded the 2016 W.K.H. Panofsky Prize in Experimental Particle Physics from the American Physical Society. The $10,000 prize, established in 1985, is given annually to recognize achievements in high energy particle physics. The 2016 prize is shared with Jonathan Dorfan, Stephen Olsen, and Fumihiko Takasaki "for leadership in the BABAR and Belle experiments, which established the violation of CP symmetry in B meson decay, and furthered our understanding of quark mixing and quantum chromodynamics," according to the prize citation.

Hitlin was the founding spokesperson of the BABAR collaboration, and Dorfan directed the construction of the PEP-II asymmetric B factory and was also the technical coordinator during construction of BABAR. Dorfan is the director emeritus of the SLAC National Accelerator Laboratory and president of the Okinawa Institute of Science and Technology. BABAR is a particle detector designed to study unstable elementary particles called neutral B mesons, composed of a third-generation bottom quark and a down quark.

BABAR, and a similar experiment called Belle, carried out simultaneously at the High Energy Accelerator Research Organization in Tsukuba, Japan, led by Stephen Olsen and his colleague Fumihiko Takasaki, made the first measurements of the time-dependent Charge-Parity (CP)-violating asymmetry in the rare decay of neutral B mesons to a J/psi meson and a short-lived neutral K meson. These results established the validity of the model of Makoto Kobayashi and Toshihide Maskawa, who showed that if there were three families of quarks, there would be a CP-violating phase. This phase could cause a difference in the decay rate of neutral B mesons and their antiparticles to this final state. This CP-violating phase could help explain why our universe is dominated by matter, while at the time of the Big Bang there were equal amounts of matter and antimatter.

In 2001, BABAR and Belle convincingly measured this CP-violating phase, finding its value to be consistent with the predictions of the model. Kobayashi and Maskawa subsequently shared the Nobel Prize in Physics in 2008 for "the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature."

"This is an award that is long overdue," says Mark Wise, Caltech's John A. McCone Professor of High Energy Physics. "The measurements by BABAR and Belle of CP non-conservation in B decays showed that the CP non-conservation observed in weak decays is intimately connected with the generation of mass for the quarks. It didn't have to be that way, and this discovery was a milestone achievement in particle physics."

While BABAR ended data taking in 2008, the analysis of the data set continues and so far has led to 550 published papers. BABAR has subsequently refined and extended its measurements to many other B meson decays as well as charm meson and tau lepton decays, that have provided compelling evidence for the validity of the Standard Model of elementary particle physics, which unifies into a single theory the smallest building blocks of matter and three of nature's four forces.

"This award recognizes the contributions of more than 600 physicists and engineers from 75 institutions in 13 countries," Hitlin says. "I was fortunate to have the opportunity to lead this extraordinary collaboration."

Hitlin arrived at Caltech in 1979 as an associate professor and became a full professor in 1986. He was the principal investigator of the Caltech High Energy Physics group from 1994 to 2010 and is a Fellow of the American Physical Society.

The name BABAR is not an acronym, as are the names of most high energy physics experiments. Rather, it is derived from the name of the elephant Babar, the main character of a set of children's books, and refers to the B and anti-B (Bbar) mesons, which are at the heart of the experiment. 

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Physicist David Hsieh Wins Packard Fellowship

Caltech physicist David Hsieh, who devises and builds new laser-based instruments in order to identify, understand, and manipulate novel phases of matter, has been awarded a Packard Fellowship for Science and Engineering. These fellowships, awarded annually by the David and Lucile Packard Foundation, "provide early-career scientists with flexible funding and the freedom to take risks and explore new frontiers in their fields," according to the foundation.

Hsieh, an assistant professor of physics, is one of 18 new Packard Fellows who will receive individual grants of $875,000 distributed over five years.

Hsieh received the news that he had been selected as a fellow at a casual meeting with Fiona Harrison, the new chair of the Division of Physics, Mathematics, and Astronomy, at the Red Door Café on campus. He was completely caught off guard. "I thought we were just meeting to talk about how things were going," he says. "Then partway through our conversation, Fiona's phone rang, and I asked if I should leave to give her some privacy. She said, 'No, you should stay. This person wants to talk to you.'"

On the other end was Xiao-Wei Wang, Packard Fellows program manager at the Foundation. Hsieh recounts that Wang asked if he was sitting in a comfortable place and then told him the good news.

Hsieh says he is honored by the recognition and excited about the freedom that the grant will provide. "Both the sum and the flexibility with which these funds can be used gives me a very unique opportunity to pursue the riskiest branches of physics that I'm interested in," he says.

He plans to explore the possibility of using light to alter the electronic phase of materials in order to manipulate their macroscopic properties. For example, he says, "Can I use electromagnetic radiation to change something from a metal to an insulator, or from a magnet to a nonmagnet?" If such tailoring of materials properties with light is possible, it could open the door to the creation of more powerful and more versatile electronic devices, potentially at a lower energy cost.

"I'm thrilled that David has won this prestigious award. It will give him the flexibility to pursue high-risk, high-reward projects," says Fiona Harrison, the Kent and Joyce Kresa Leadership Chair of the Division of Physics, Mathematics, and Astronomy and the Benjamin M. Rosen Professor of Physics. "Being there when he heard the news was definitely a highlight of my job as division chair so far."

Hsieh earned his BS in physics and mathematics in 2003 from Stanford University and his PhD from Princeton University in 2009. He was a Pappalardo Fellow at MIT before joining the Caltech faculty in 2012.

He joins 23 other current Caltech researchers who have been named Packard Fellows since the program's inception in 1988. To date, the Packard Foundation, a private family foundation created in 1964 by Hewlett-Packard Company cofounder David Packard and his wife, Lucile, has awarded $362 million to support 541 scientists and engineers from 52 national universities. Each year, participating universities are invited to nominate two faculty members for consideration by the 12-member Fellowship Advisory Panel of internationally recognized scientists and engineers, which recommends nominees for approval by the Packard Foundation Board of Trustees. 

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Robotic Astronomer Finds New Home

When it comes to telescopes, bigger is almost always better. Larger telescopes collect more light, enabling them to see the farthest and faintest objects in the sky. But older and smaller telescopes can still do important science—and, when a less-in-demand, smaller telescope is equipped with an autonomous, robotic, state-of-the-art laser adaptive optics system to erase the atmosphere's blurring effect, the data that can be obtained give us a unique window on the universe around us.

For the last three years, the world's only robotic adaptive optics system, Robo-AO, has been making new discoveries with the 60-inch telescope at Caltech's Palomar Observatory north of San Diego. One of the major projects that Robo-AO undertook was a comprehensive study of stars that were identified by NASA's Kepler space telescope as likely to host planets. Now, the instrument, developed at Caltech, is moving to a new home: the 2.1-meter telescope at Kitt Peak National Observatory in Arizona.

The hallmark of Robo-AO is its efficiency. Whereas other adaptive optics systems must be monitored and set up by several people, Robo-AO is fully robotic, which makes it 10 times more efficient than any other adaptive optics system in the world. Robo-AO is a joint project of the Caltech Optical Observatories (COO) and the Inter-University Center for Astronomy and Astrophysics (ICUAA) in Pune, India, guided by principal investigator Christoph Baranec (BS '01), a former Caltech postdoc (now a professor and Sloan Research Fellow at the University of Hawaii), and co-principal investigator Professor A. N. Ramaprakash of the IUCAA.

Budget cuts forced the National Optical Astronomy Observatory, which operates the Kitt Peak Observatory for the National Science Foundation, to seek new operators for the observatory's 2.1-meter telescope. "We immediately sent a proposal," says Shri Kulkarni, Caltech's John D. and Catherine T. MacArthur Professor of Astronomy and Planetary Science and director of the COO. "The larger size of the telescope and the excellent site made for a perfect match between Robo-AO and the 2.1-m telescope." The proposal won. Funding for three years of operation was provided through a $1 million dollar donation from Rohan Murty—an entrepreneur based in Boston and Bangalore—and his family. "Automating the discovery of the universe impacts one of mankind's oldest activities: to look up at the heavens and wonder about our place in the universe," says Murty. "This activity has been the source of inspiration for religion, poetry, literature, science, and culture in general. Hence, I am pleased to support a dedicated telescopic facility for Robo-AO, which will serve as a new frontier for what computer science can do for astronomy and for mankind, in general."

"What Robo-AO is best in the world at doing is large surveys at high angular resolution," says Reed Riddle, the project scientist for Robo-AO's Kitt Peak operation. This makes it ideal for follow-up observations of the candidate planetary systems that Kepler continues to find. Kepler detects exoplanets when they pass in front of, or transit, their stars, causing a slight dip in starlight. This allows astronomers to both discover and measure the sizes of thousands of exoplanets. "However, if another star is close to the target star, it dilutes the depth of the transit dip, which means we measure incorrect sizes for the planet candidates," says Nicholas Law, a former Caltech postdoc who is now a professor at the University of North Carolina, Chapel Hill, and a Robo-AO team member. Astronomers must study these planets in more detail to confirm that they are real and not a spurious reading caused by nearby stars. To date, Robo-AO has evaluated about 90 percent of Kepler's targets—some 3,300 potential planetary systems. In comparison, astronomers using all other adaptive optics systems in the world put together have investigated far fewer of the Kepler planet candidates.

But Robo-AO can do much more than evaluate exoplanets, Kulkarni notes. "As a dedicated facility, Robo-AO on the 2.1-m telescope can undertake other long-term studies, such as monitoring weather on Neptune, and large surveys, such as tracking and resolving asteroids. Furthermore, it is an excellent opportunity for young people to have hands-on experience with a state-of-the-art facility," he says. Indeed, Caltech graduate student Rebecca Jensen-Clem will be using Robo-AO for her thesis project to study weather on brown dwarfs, and postdoctoral fellow Dmitry Duev, though trained in radio astronomy, plans to use the facility for an ambitious study of binarity in asteroids—whether an asteroid is part of a single or double system (observing a binary orbit allows for a measurement of the masses of both members of the pair).

Over the past two decades, adaptive optics has revolutionized astronomy, giving ground-based telescopes the ability to obtain pristine views that previously had been possible only from space. Adaptive systems, now found on all large telescopes, such as the Keck Observatory in Hawaii, send a laser beam into the sky, where the light scatters off air molecules and returns to the telescope, traveling through the same atmospheric turbulence that blurs the telescope's images. Once a detector measures this blur, a deformable mirror can then warp the light in such a way that the distortion is precisely canceled out.

"Don't get me wrong, the adaptive optics on big telescopes offer us the best angular resolution," says Baranec, who also serves as the Robo-AO instrument scientist.  Robo-AO, with its high on-sky efficiency, excels in its ability to observe a large sample rapidly. Using its data, astronomers are working to determine how the prevalence of giant gas planets close to their stars depends on the presence of a companion star. Robo-AO also has discovered one of only two known quadruple star systems containing planets. Twenty science papers have been published since the system was commissioned three years ago, and several more are in progress.

In this same vein, Robo-AO has surveyed 3,000 of the nearest stars searching for multiple star systems (our solar system has only one star but many others contain stars two, three, even more stellar companions). Robo-AO will continue this program, investigating tens of thousands of stars in a survey Kulkarni describes as undertaking "galactic geography."

And there will be more extrasolar planets discovered. The Kepler mission is winding down, but its successor, the Transiting Exoplanet Survey Satellite, scheduled for launch in 2017, is expected to find tens of thousands of new worlds—which Robo-AO will be uniquely suited to study. "The Robo-AO team is making one-sixth of its observing time available to the U.S. astronomical community. In addition we have had discussions with several colleagues at astronomy departments in the U.S., India, and Europe with the view of expanding the range of astronomical research that can be undertaken by Robo-AO," Kulkarni says.

So while it may not be the biggest system in use, Kulkarni says, Robo-AO does its job very well. "Not everything has to be big telescopes or big space missions," he says. "It's a little celebration of less-is-more."

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Patrick Rall: A Passion for Entanglement

SURF participant Patrick Rall and a summer of quantum information science.

For senior Patrick Rall, a native of Munich, Germany, the summer offers one of the year's few chances to visit home. But for the last two summers, Rall, a Caltech physics major, has been spending his summers on campus, drawn by another opportunity—the chance to conduct cutting-edge research while being mentored by John Preskill, the Richard P. Feynman Professor of Theoretical Physics, as part of the Institute's Summer Undergraduate Research Fellowships (SURF) program. Last year, Rall worked in the laser lab of Assistant Professor of Physics David Hsieh on a condensed matter physics experiment. This summer, he switched his attention to quantum information science, a new field that seeks to exploit quantum mechanical effects to create next-generation computers that will be faster and more secure than those currently available.

A key idea in quantum mechanics is superposition of states. Subatomic particles like electrons can be described as having multiple positions, or more than one speed or energy level. This is illustrated by the thought experiment developed in 1935 by Austrian physicist Edwin Schrödinger. In it, a cat is placed into an imaginary box containing a bottle of poison, radioactive material, and a radiation detector. If a radioactive particle decays and radiation is detected inside the box, the poison is released and the cat is killed. But according to quantum mechanics, the cat could be simultaneously alive and dead. Yet if one were to open the lid of the box, the cat would become alive or dead. By opening the box, we have destroyed the quantum nature of the state; that is to say, the observation itself affects the outcome, and yet that outcome is randomly determined.

"Where this gets really interesting is when more than one cat gets involved," Rall says. "Then we can have states where looking at one cat determines the outcome of looking at the other, even if they are on different continents or even different planets. For example, I cannot know if I will see a live or a dead cat upon opening either box, but I can know that the cats are either both alive or both dead."

This "spooky action at a distance"—as Einstein phrased it—is called entanglement, and an entangled state, physicists say, can store information. "When looking at systems with many cats, the amount of entanglement information is much larger than what I can obtain by looking at the cats individually," Rall says. "To harness the sheer quantity of information stored in these so-called many-body systems, we must better understand the structure of these spooky correlations. This is what I worked on this summer."

Quantum many-body systems are difficult to simulate on a computer, but by looking at small-enough systems and using mathematical tools, researchers can study complex entangled quantum states. Physicists have been studying many-body entanglement for a long time because of its importance in understanding certain semiconductors.

"This summer, I had the privilege to work under Professor Preskill, and that was an incredible experience," Rall says. A central interest of Preskill's lab is to design schemes for quantum computation. Modern computers use classical bits—ones and zeroes—to store data. A quantum computer would use quantum bits—or qubits—and use their superposition and entanglement to perform computation. Quantum computers, while still in the experimental stage (with heavy investment from companies like IBM, Microsoft, and Google), have been touted for their potential to generate unbreakable codes and to efficiently simulate many complex systems, with implications for computational chemistry and biology.

"The most interesting thing about the quantum computer is that we have no idea what it could be capable of," says Rall. "We know some quantum algorithms that are faster than the best-known classical algorithms. But what are the limits? Nobody knows."

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A Passion for Entanglement
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SURF Profile: Patrick Rall
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Senior Patrick Rall has spent the last two summers conducting cutting-edge research in quantum information science.
Wednesday, November 11, 2015
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