Students create exotic state of matter

By Bennett McIntosh

IN THE SUMMER OF 2015, Princeton students Joseph Scherrer and Adam Bowman experienced something few undergraduates can claim: they built, from scratch, a laser system capable of coaxing lithium atoms into a rare, highly excited state of matter to reveal their quantum nature.

When they joined Assistant Professor of Physics Waseem Bakr’s lab in the spring of 2014, Scherrer and Bowman had little experience in optics or quantum physics. Their task was to convince lithium atoms to enter a state of matter known as the Rydberg state. In this state, each atom has a very high-energy electron located far from the atom’s nucleus. The separation of the electron’s negative charge from the nucleus’ positive charge creates a dipole, like a magnet’s north and south poles.

To give the electrons the right amount of energy to create the Rydberg state, Scherrer and Bowman hit the atoms with two carefully tuned lasers, first blue and then red. To prove that the lithium atoms had indeed entered the Rydberg state, the two researchers needed a way to detect them. They trawled the scientific literature for a sensitive enough detection method, and eventually implemented a technique called electromagnetically induced transparency. With this technique, the Rydberg atoms interfere with the absorbance of certain wavelengths of light, so if the gas is transparent in those wavelengths, the Rydberg atoms are present.

The undergraduates designed and built the device independently, Bakr said. “I wasn’t planning on starting this, and suddenly it grew into a whole project, largely due to their efforts,” he said.

“It was a turning point in our scientific development,” said Scherrer, who graduated in 2016 with a degree in physics. “For me, it was a realization of what you can do with quantum optics.” Scherrer was awarded a Fulbright grant to join a team in Munich, Germany, where he is building electron microscopes to image the brain. He will next head to the Massachusetts Institute of Technology to pursue a Ph.D. in physics. Bowman, a physics major in the Class of 2017, continues to study the physics of electronically interesting materials, and spent his junior year and the summer of 2016 working on a new project with Ali Yazdani, Princeton’s Class of 1909 Professor of Physics. There, Bowman built a device that works like an inkjet printer for atoms to print superconductors layer-by-layer.

Atom catcher: With lasers and magnets, Waseem Bakr traps atoms for study under the microscope

By Bennett McIntosh

THE COLDEST SPOT on the Princeton campus is a cluster of a few thousand atoms suspended above a table in Waseem Bakr’s laboratory. When trapped in a lattice of intersecting lasers at just millionths of a degree above absolute zero — and roughly one-millionth the density of air — atoms become very still, enabling Bakr, an assistant professor of physics, to study them through a microscope.

At these frigid temperatures and ultralow densities, atoms begin to act very strangely. They function less like individual particles and instead behave like waves that blur and overlap, losing their individual identity and trading the physics of the everyday world for the laws of quantum mechanics. The resulting state, known as a degenerate Fermi gas, can yield insights into new states of matter that someday may lead to applications such as superconductors and quantum computers.

Bakr uses a system of lasers and magnetic fields to cool and trap the ultracold atoms in a crystal-like lattice made from light. He then manipulates and observes the atoms using a quantum-gas microscope, a device that he helped invent during his graduate studies with Markus Greiner at Harvard University, and further improved when he was a postdoctoral researcher with Martin Zwierlein at the Massachusetts Institute of Technology.

“We use lasers to create artificial crystals in which we place these quantum-mechanical atoms where the spacing between atoms is 10,000 times larger than what you find in real crystals,” Bakr said. “We are essentially engineering the behaviors of atoms using light.”

Bakr and his team first heat a block of lithium to 800 degrees Fahrenheit to liberate individual atoms that then fly into a long tube. There, the particles collide head-on with a laser beam pointed in the opposite direction, which rapidly slows and cools them. The atoms then flow into a chamber where the intersection of several laser beams creates an electromagnetic field that confines the atoms in an “optical trap.” The trap allows the fastest-moving (and warmest) atoms to escape, further cooling the ultracold gas. The resulting cluster of atoms, Bakr said, is “the coldest stuff you can find in the universe.”

Using the microscope, Bakr can agitate a single atom to watch the disturbance propagate, or he can rearrange the entire system to simulate a different material. “If I decide I want to study graphene today,” he said, “I can arrange my lasers to make a graphene-like lattice, and suddenly the physics that I’m looking at are very different.” This precise control could hold the key to another advance, he said. “If you have 1,000 atoms, and you have control over every single atom and their interactions, these are the basic building blocks of a quantum computer,” Bakr said.

Cold atoms

Trapped by lasers and magnets, lithium atoms form a fluorescent red ball at the center of this image. In this initial stage of laser cooling, about 1 billion atoms are brought from a temperature of 350 degrees Celsius to a thousandth of a degree above absolute zero.

Bakr and his team are using ultracold atoms to study the behavior of superfluids with imbalanced spin populations. In a paper published in the August 24, 2016, issue of Physical Review Letters, Bakr and his team showed that the two-dimensional gas separates into two phases, a superfluid in the center of the trap and a  normal gas at its periphery, like the phase  separation that happens when mixing oil and  water. “Observing this phase separation is the first step in a search for exotic types of superfluidity that were predicted over 50 years ago,”

The Bakr lab’s work is supported by grants from the Air Force Office of Scientific Research, the National Science Foundation and the Alfred P.  Sloan Foundation.

Behind the curtain: Scandal, tragedy, art and politics at the Bolshoi

By Jamie Saxon

ON THE NIGHT OF JAN. 17, 2013, a hooded assailant approached Sergey Filin, artistic director of the Bolshoi Theater Ballet, and flung battery acid in his face. The crime made international headlines and stunned a community of artists known for elegance rather than violence. Some months later at a gala at the Kremlin, Simon Morrison, a professor of music and an expert on 20th-century Russian and Soviet music and ballet, met Filin, who had undergone numerous operations in Germany and had lost all of his sight in one eye.

“You could still see the scars on his neck from the acid,” Morrison said. “He wore these dark wraparound glasses and had an attendant with him administering drops. It was horrific, deeply macabre.”

Bolshoi Confidential: Secrets of the Russian Ballet from the Rule of the Tsars to Today

In his new book, Bolshoi Confidential: Secrets of the Russian Ballet from the Rule of the Tsars to Today (W.W. Norton & Company, 2016), Professor of Music Simon Morrison weaves a richly detailed account of the Bolshoi Ballet from its origins in 1776 under Catherine the Great through its glorious history as a cradle for high art, political intrigue and shocking scandal. Book cover courtesy W. W. Norton & Sons.

Morrison’s encounter with Filin inspired him to explore whether the Bolshoi — a symbol of Russia presented to the world as a great cultural icon — had been roiled by these types of scandals in the past, and what that said about the institution historically and politically. He wrote a piece about the attack for the London Review of Books, prompting a literary agent to suggest that he write a book about the incident.

Morrison knew that the story of the attack, despite its tragedy, would not on its own have a lot of traction or depth as a book. He had to get into the history of the organization, explore the archives and talk with other scholars. To learn more about how art and politics intersect at the Bolshoi, Morrison began an intensive three-year research process.

The result is a richly detailed account of the crown jewel of Russian culture, considered an emblem of power by the government since its founding in 1776, according to Morrison. “It is a tale about the kind of negative pressures that lead to the creation of great art,” he said. “One of the morals of the story is that in the Soviet experience there’s something about immense censorship, repression and threat that leads to the production of masterpieces. The Bolshoi has been burned and rebuilt and almost liquidated numerous times, yet has produced some of the world’s greatest ballets, including Swan Lake.”

A member of the Princeton faculty since 1998, Morrison has been diving deep into the Moscow archives — once with mittens on his fingers — for nearly two decades and knows them well. He also knows the art of “gentle pestering” often required to access them. Morrison earned his Ph.D. in music history from Princeton in 1997, and his previous works include Russian Opera and the Symbolist Movement, The People’s Artist: Prokofiev’s Soviet Years, and Lina and Serge: The Love and Wars of Lina Prokofiev, a biography of Prokofiev’s first wife.

His research for Bolshoi Confidential took him into the small theater museum at the Bolshoi and the immense theater and dance archives in the Bakhrushin Museum as well as the Russian State Archive of Literature and Art and the Russian State Archive of Social Political History, which houses the records of the Central Committee (the operating division of the Stalinist government in the Kremlin), among others. He also enlisted the help of freelance archivist Ilya Magin, whom he said was indispensable for researching the Imperial era in the St. Petersburg archives. In addition, Morrison conversed with dance critics and historians in Moscow “who have lived and breathed ballet all their lives.” He even wrangled an invitation to spend the day at the dacha, or country house, of Yuri Grigorovich, ballet master from the Khrushchev-Brezhnev era into the 1990s, now almost 90.

Among the gems Morrison uncovered was an enormous box of bureaucratic correspondence about the search for a real donkey for the ballet Don Quixote, created by the famous choreographer Marius Petipa. During the ballet’s first run in St. Petersburg in 1869-70, a female donkey was borrowed from a nearby vaudeville show. “This poor thing had a heart attack and died on the stage during a rehearsal,” said Morrison, who read the long veterinary report. In Moscow, the Bolshoi used a male donkey from the Moscow Zoo. “This donkey was trotted in with its minder from the zoo to the theater every day for the show and there was a budget for ‘treats in the form of bread and oats’ for the donkey. To the present day in Moscow, they use a donkey in Don Quixote,” he said.

Stalin at the Bolshoi

Professor of Music Simon Morrison explores how the Bolshoi Ballet was used throughout history as a political tool. Pictured is Joseph Stalin (fourth from right), former leader of the Soviet Union, attending the Bolshoi in the mid-1930s. (Photo courtesy of the Russian State Archive of Literature and Art)

Throughout its storied past and to this day, the Bolshoi — the theater and its eponymous ballet company, arguably the finest in the world — has been indelibly controlled by the government — culture and politics, performers and bureaucrats, forever entwined. For example, the iconic Soviet ballet of the late 1920s, The Red Poppy, a tale of Soviet sailors who are detained in China, is about the Stalinist regime’s involvement in the rise of Communist China. “The Central Committee decided when and how this ballet would be produced and performed in 1927,” Morrison said.

The Bolshoi, with more than 2,000 seats, was a kind of political convention center during the Soviet period, Morrison said, and was used for the signing of the Soviet Constitution in 1935. After the Revolution, Vladimir Lenin gave speeches there.

In 2005, at the start of its most recent renovation — which took six years and cost $680 million — the theater was gutted and boxes of ancient materials were found in the basement and attic. Soldiers were brought in to move the materials into the administrative building next door. “There is always that connection between arts and the government,” Morrison said. “The Bolshoi is a national treasure.”

Dancers practicing

Elizaveta Gerdt, one of the few ballerinas who did not leave Russia after the Soviets took over, instructs Bolshoi ballet dancers Maya Plisetskaya and Vladimir Preobrazhensky in 1947. (Photo Courtesy of the Russian State Archive of Literature and Art)

While once accessible to people of all classes with affordable tickets in the Soviet era, today the Bolshoi is no longer “the people’s house,” Morrison said. Tickets can cost as much as $500. “It’s a kind of playground for the petrolruble crowd in that way in which oligarchs now control so much of the culture in Russia, much of it eroded into popularized entertainment.”

But still the Bolshoi Ballet goes on. In late May, Pavel Dmitrichenko, the dancer who was convicted of and imprisoned for organizing the attack against Sergey Filin, was released on bail having served only half his sentence. “He now wants to dance again at the Bolshoi,” Morrison said. “If he does, which I think is 50-50 at this point, he may well be performing in the ballet that he was performing in when he was convicted, which is Ivan the Terrible. If that happens, the perverse ironies pile up because Ivan the Terrible is rumored to have blinded the architects of St. Basil’s Cathedral on Red Square to ensure that they never again built anything as beautiful. Dmitrichenko’s rehabilitation is so implausible that it is almost guaranteed of happening. Ballet is like that.”

Big answers from small creatures

A graduate student tracks the spread of viruses from bats to humans in Madagascar

By Cara Brook

IT IS SPRINGTIME in the Makira-Masoala peninsula of northeastern Madagascar, and the lychee trees are in full fruit. I sit crouched with my research team in camping chairs as dusk settles, our eyes intent on Rousettus madagascariensis, one of three species of endemic Malagasy fruit bat. The fox-faced bats flit deftly amongst the leafy branches, dodging our nets as they search out juicy pink fruits for their evening meal.

Our quiet vigil is interrupted by the arrival of a whistling gray-haired man from the nearby village who carries a net strung on a pole in one hand and a garish yellow plastic fuel can in the other. With a nod to us, he strides up to a neighboring tree and expertly scoops five of the feasting bats, pins the net to the ground with a bare hand, and coaxes the bats one-by-one into his yellow can. Mission accomplished, he straightens up with a wink and turns back home, rattling his can of bats in time to his whistle as he walks.

Handeha hihinina andrehy izy?” I ask my Malagasy colleagues in astonishment. Is he going to eat the bats? Laughing at my horror, they nod in affirmation.

Bats as reservoirs

I study zoonotic diseases, infections that transmit from wildlife to humans, as a graduate student in Princeton’s Department of Ecology and Evolutionary Biology. Bats are native reservoir hosts — meaning they host viruses without getting sick — for a number of the world’s most dangerous human diseases, including rabies, Ebola and SARS. I want to understand how bats host these viruses without getting sick and what factors contribute to the viruses’ spillover to human populations.

Field lab

Graduate student Cara Brook (rear) and colleague Christian Ranaivoson, a graduate student at the University of Antananarivo and an intern with the Pasteur Institute of Madagascar, process fresh bat fluids in their field lab in Maromizaha, Madagascar, in September 2014. (Photo by Deborah Bower.)

A lot of my work involves building mathematical models to understand disease. When I started graduate school, I barely understood what a “model” was. Four years later, I recognize that a model is simply a representation of reality — it can be physical, like a model of the solar system; experimental, like a mouse that a scientist infects to monitor disease progression; or mathematical, like the equations we use to describe disease transmission in my field of disease ecology.

The goal is to build simple models that still adequately represent reality. One of my professors, Bryan Grenfell, once told me, “If you apply a complex model to a complex system, then you have two things that you don’t understand.” If we can understand our models, then we can learn by observing the differences between these models and the more complex reality.

In disease ecology, our simple models are mathematical equations that class all potential disease hosts — bats, in my research — into three categories: (1) susceptible to infection; (2) currently infected; or (3) recovered from infection and now immune. We use our equations to predict how the proportion of hosts within each category changes over time, and then we collect data to determine whether our predictions match reality.

Remote corners

One of the ideas we are testing is whether bats are fundamentally different from other mammals in their capacity for resisting or tolerating viral infections. I build models depicting the spread of infected cells within individual bats and explore the physiological processes that might allow a bat cell to host a replicating virus without experiencing the cellular damage that causes the host to feel sick.

In the lab, I grow layers of bat cells, infect them with virus, and monitor cell-to-cell viral spread. Then I compare these data with what is predicted in my models. If the data match the model, then maybe the mechanism for disease mitigation that I chose for my model also is the one used in real life.

At a population level, bat-virus transmission, including spillover, peaks in the winter, and we want to know why. I build population-level transmission models that incorporate different seasonal pathways to cause winter infections, then I try to match those models to data. Collecting field data is hard — I spend years trekking to remote corners of Madagascar, mastering obscure Malagasy dialects, and rigging complex pulley systems out of nets, fishing lines and carabiners.

At the end of it all, like the man in Makira- Masoala, I catch a few bats. Instead of cooking them for dinner, however, I use fine-gauge needles, cryogenic vials and sterile swabs to collect their blood and other bodily fluids before I let them go. I haul the fluids in vats of liquid nitrogen to the laboratories of the Pasteur Institute of Madagascar in the capital city of Antananarivo. From there, samples are shipped to collaborators in London, Berlin, New York and Washington, D.C., while others remain in-country. My collaborators and I perform a variety of tests on these transported fluids to ascertain whether the bats were susceptible, infected or recovered from infection at the time of sampling.

When all is said and done, the results are sometimes difficult to interpret. Science is a gradual process, and the goal is to always narrow the window of possible hypotheses at least a little bit.

For me, science is a recognition of, as John Steinbeck put it, “how man is related to the whole thing.” I’m still trying to understand how humans fit into the zoonotic cycle of disease. I’m nearing the end of my Ph.D., but I have enough questions to keep me going for a lifetime.

Cara Brook is a fifth-year doctoral student. Her advisers are Andrew Dobson, professor of ecology and evolutionary biology; Bryan Grenfell, the Kathryn Briger and Sarah Fenton Professor of Ecology and Evolutionary Biology and Public Affairs; Andrea Graham, associate professor of ecology and evolutionary biology; and C. Jessica Metcalf, assistant professor of ecology and evolutionary biology and public affairs. Brook’s research is funded by the National Science Foundation, the National Geographic Society and PIVOT, a Madagascar-based health care nongovernmental society.