22 September 2022

The (Atomic) Clockmaker

How a woman from Colombia overcame obstacles to become a leading theoretical physicist and develop the world’s most accurate atomic clock.


The Rey Family
A young Ana Maria Rey and her parents, Bogotá, Colombia (1993).

In the early 1990s, a student who would become one of the leading theoretical physicists of our time was completing her high school physics homework. Suddenly an explosion shook her family home in Bogotá, Colombia's capital city. Her windows vibrated, and Ana Maria Rey realized a bomb had detonated close to her apartment. The target was a nearby police station. Car bombs were common during the decades of conflict between the Revolutionary Armed Forces of Colombia joined by Colombia’s drug cartels and the Colombian government. Terrorism gripped the city for many years. Some incidents, like the 1985 Palace of Justice siege and the 1993 bombing of the Centro 93 shopping mall, made world headlines. Rey and her school friends grew up terrified to go to shops, movies or restaurants. Everywhere they went, the Rey family had to open the trunk of their car so the police could check for explosives. Despite the looming threat of terrorism, Rey managed to escape the madness, immersing herself in her schoolwork. 

Rey found her calling after a eureka moment in her first physics class. “All the numbers and concepts in my mind came to life.” She realized problems in the real world could be solved with theory. “I felt the beauty of physics. It governs our universe, from the movements of electrons inside an atom to the behavior of black holes. It was a puzzle that could tell us everything about the world, and I loved solving it.” She was captivated. “All I wanted to learn about was physics, no matter what language it came in. My teacher brought me advanced textbooks, which I read in English.” However, to pursue physics she had to overcome the wishes of her family who were set against any career in science.

“You’ll end up becoming a taxi driver,” warned Rey’s parents when she told them she wanted to study for a degree in physics. After investing substantially in her education, her mother and father felt studying abstract theories would give her few prospects for finding a suitable career. "You need to find a 'real' job," Rey's father told her. Her mother was a Senior Associate Dean and a faculty member of the economics department at Universidad del Rosario. Her father was general manager of the Sorteo de Navidad, Colombia's most prestigious national lottery. When he was young, Rey's father wanted to become a mathematician, but his parents persuaded him against it. He was grateful for their advice given his successful career and wanted the same for his daughter. The Reys tried to steer their daughter but remained supportive. "We will pay for you to study for an engineering or law degree and get as many classes as you want, but physics definitely isn't an option for a long-term career,” they told her. Like her father, Rey followed her parents’ advice and chose to take an engineering course. She began to prepare mentally for a practical life — a far cry from the world of theoretical physics she loved. But then, out of the blue, everything changed.

"You need to find a 'real' job," Rey's father told her.

After taking the national matriculation exam to get into university, she got a surprising phone call. Not only had she scored the highest ICFES grade in her school but the second-highest mark in Colombia. She could not believe it. Not long after she applied to the Universidad de los Andes, one of Colombia’s leading private research universities, she was offered an undergraduate fellowship in the faculty of art and science, covering all her tuition fees. Having her own funding meant she was now financially independent. She canceled her engineering application and immediately changed it to physics. She was now set to pursue the life she had dreamed of after her first physics class.

When Rey grew up in Bogotá, Colombia in the 1990s, terrorism gripped the city. Conflict between the Revolutionary Armed Forces of Colombia, the drug cartels and the government raged for many years.

Rey loved studying at the Universidad de Los Andes, but it would always be too small for her long-term ambitions. “We were a tiny unit of seven people, with incredibly small classes and personalized education. It was a wonderful five years, and I met my husband there. But there were no Ph.D. opportunities for my subject in Colombia. To continue with physics, I had to go abroad." She set her sights on America and applied to the University of Maryland at College Park. Given that the school had a good track record with people from Colombia, it was a place she and her husband could both find opportunities. After completing her thesis on understanding how a rotating black hole affects the polarization of light propagating nearby, she graduated Magna Cum Laude from the Universidad de Los Andes with a bachelor’s degree in physics. Shortly after, she gained a two-year research fellowship at the University of Maryland.

Making connections within the community of optical scientists completely transformed her career. When she arrived in Maryland in 2000, her initial trajectory was not what she had envisioned. “I wanted to study something more applied. My main interest was non-linear optics, but my assistantship was in plasma physics. I worked on it for half a year, but, in the end, it wasn’t for me.” Then as part of the introductory physics lecture series, William Phillips, who had won the Nobel Prize for trapping and cooling atoms, gave a talk to the incoming Ph.D. students. Phillips’ specialist subject of Atomic Molecular and Optical (AMO) physics excited Rey. After the lecture, she approached Phillips, and the conversation had a profound influence on her career. "After I heard Bill's speech, I had no doubt that this was what I wanted to do. I went straight to my professor in plasma physics and explained everything. He knew someone at the National Institute for Standards and Technology (NIST) connected with Bill’s and Prof. Charles W. Clark’s groups, and that was it. I made an appointment to talk to them as soon as I could.” 

"I felt the beauty of physics. It governs our universe, from the movements of electrons inside an atom to the behavior of black holes."

She quickly went from being an outsider in a new country to working on equal terms with luminaries in the field. “I went to NIST, where Bill and Professor Charles W. Clark worked. I asked if I could join and do some research, to which they both said ‘yes, come along.’ It was a dream!” Rey began working under Clark, who introduced her to trapping atoms in optical lattices—a device to hold atoms like an egg box made entirely from laser beams. Her work involved models to describe the quantum behavior of atoms frozen near absolute zero, temperatures at which they hardly move, and instead tunnel quantum mechanically when loaded into optical lattice. Her goal was to study how collisions between atoms modify their quantum behavior. 

Rey’s collaborative approach with other scientific communities helped make her Ph.D. theoretical work one of the most advanced and broad at that time, since it covered concepts ranging from Atomic Molecular and Optical Physics to cosmology. While refining her understanding of atoms trapped in optical lattices Rey noticed that the classical methods for studying ultracold atoms, Gross-Pitaevskii (GP) equations, were not entirely accurate. Although they worked for dilute gases in the bulk, the equations were not accurate for the dense conditions reached when atoms are tightly trapped in an optical lattice. She looked to scientific communities that few would typically associate with AMO physics. “I thought it was crucial to be open-minded and reach out to other fields. I became aware that cosmologists have worked on similar topics when modelling the early universe and had already developed more advanced methods to describe the complex quantum dynamics. People in my field didn’t even know about these methods. So I went to see how they could help. I worked on adapting their methods to ultracold atomic gases and developed new tools that refined our understanding of atomic behavior beyond the traditional GP equations. These methods helped guide the first experiments exploring the complex quantum dynamics displayed to interacting atoms in optical lattices.”

Ana Maria Rey
Ana Maria Rey. Credit, John D. and Catherine T. MacArthur Foundation

With a new understanding of atomic collisions, Rey’s theory allowed precise measurements of time that led directly to applications in timekeeping, quantum simulations and the development of the world’s most accurate atomic clock. Used every day where timing around the world needs to be in complete harmony, atomic clocks are essential for our way of life. They determine Universal Time across the internet to keep computers worldwide running in sync and are critically important to calculating GPS positions.  Rey’s goal was to make them even more accurate. “The team at JILA (a joint institute of the University of Colorado Boulder and NIST) were working on atomic clocks and wanted to have lots of atoms to enhance their signals. Introducing many atoms meant they bump into each other more frequently, leading to more collisions. This only made things more confusing. I developed a model to understand collisions and how to suppress and ultimately control them. This control allowed us to measure time even more precisely. It is useful in atomic clocks and has given us a better understanding of quantum mechanics." 

Today, Rey is among the world’s most renowned theoretical physicists. Her hard work, determination and overwhelming love of physics have gained numerous awards and accolades. In 2013, her research into atomic behavior won her one of the United States’ most prestigious honors for intellectual and artistic achievement, the U.S. $625,000 MacArthur Foundation Fellowship. The same year, she won the Presidential Early Career Award for Scientists and Engineers, the highest honor bestowed by the US government on outstanding scientists and engineers in the early stages of their careers. A year later, she achieved two more accolades: the Early Career National Hispanic Scientist of the Year and the Maria Goeppert-Mayer Award of the American Physical Society, a recognition for outstanding contributions to physics research by a woman. She also became the first Hispanic woman to win the Blavatnik Awards for Young Scientists in 2014.

"I want to guide experiments on building synthetic quantum matter that can produce unprecedentedly accurate atomic sensors capable of unravelling the deepest secrets of our universe."

Looking to the future, Rey remains focused on the quantum world. In her most recent work, done in close collaboration with the JILA optical lattice clock, they have observed the gravitational redshift predicted by Einstein's theory of general relativity within a millimeter-scale sample. Together with the ion trapping group at NIST, the team created a quantum crystal ten times more sensitive than any atomic sensor. This experiment is currently on the edge of a major breakthrough in the hunt for one of the universe's most elusive substances — dark matter. “My goal is to advance the frontiers of material science and learn how to control quantum properties of atomic systems. I want to guide experiments on building synthetic quantum matter that can produce unprecedentedly accurate atomic sensors capable of unravelling the deepest secrets of our universe.”

Ana Maria Rey
Ana Maria Rey, (2013) MacArthur Fellow. Credit: John D. and Catherine T. MacArthur Foundation.

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