Nicholas Rivera

Massachusetts Institute of Technology

During high school Nicholas Rivera became fascinated with physics and the way atomic-scale properties explain our world: why the sky is blue, why lasers exist and how elements react with others. “The alluring thing is the idea that if you can control these microscopic properties then you can change the macroscopic world around you,” he says.

At New York City’s Stuyvesant High School, the Department of Energy Computational Science Graduate Fellowship (DOE CSGF) recipient began teaching himself about electromagnetism, quantum mechanics and other physics topics. His chemistry teacher introduced him to Glen Kowach at City College of New York, and Rivera worked with him on depositing thin chemical films to build electronic surfaces. That experience – talking through cutting-edge scientific ideas and designing and carrying out experiments to test hypotheses – set Rivera’s course. By the time he started his undergraduate degree at the Massachusetts Institute of Technology, he already planned to attend graduate school. “If you really want to do something completely fundamentally new, it makes sense to try and go for a Ph.D.,” he says.

Rivera initially considered a chemistry major but soon decided he was most interested in the physics underlying molecular behavior. He briefly worked on research studying black holes before joining physicist Marin Soljačić’s laboratory. He’s still there.

Soljačić’s group focuses on optical materials, and for the past six years Rivera has explored theories of how their atomic arrangements can influence or control the properties of photons – packets of light – they emit. “There are so many big practical problems in optics that require new fundamental approaches,” Rivera says. “So it felt like a gold mine to me.”

Rivera: X-rays

Rivera and his MIT colleagues published a Science paper exploring theoretical strategies to coax atoms to emit photons in ways or at wavelengths considered forbidden because they are prohibitively slow. The team described how interactions between atoms and electromagnetic fields within nanomaterials could produce entangled photons for quantum computing technologies, improve the solar-energy-absorbing capacity of materials and new technologies for studying molecular behavior.

That highly successful undergraduate project has fueled Rivera’s Ph.D. research. In one project, he showed that nanometer-sized structures could prompt optical materials to emit pairs of entangled photons rather than just one. Such photon pairs would be useful for quantum technologies.

He also has explored how researchers could build table-top X-ray sources, rather than relying on miles-long electron accelerators that cost billions of dollars. He and his colleagues have examined whether they can confine electrons and deflect them off nanomaterials to produce X-rays.

Most recently Rivera has used parallel computing approaches to explore whether a beam of free electrons moving through a nanostructure can amplify photons to produce a coherent light source, like a light saber. Such a mechanism would work with silicon-based nanostructures, so it could support optical processors that use photons for calculations. Rivera continues to wrestle with theoretical questions, but he’s also branching into experimental research, particularly to expand on his free-electron-laser research.

Rivera plans to graduate in August 2021 but expects to remain in his MIT group for up to two years as a postdoctoral researcher to complete his projects. He aims for an academic career; he teaches and mentors an average of three MIT undergraduates each semester. With his most recent group, he developed set of lecture notes and resources and taught the students about optical-materials research in a course-like format. “It not only helps me understand things better, but I just really like teaching.”

The DOE CSGF program of study, Rivera says, provided the extra push to broaden his knowledge with courses in applied mathematics and computation. “I learned a lot of skills – new languages that I didn't know before, new math tricks that I didn't know before. So it had a very immediate impact.”

Image caption: Nicholas Rivera and his MIT colleagues have explored a new light-emission process that can generate X-rays. As free electrons moving at nearly the speed of light approach nanomaterials, they can scatter off of quantum vacuum fields, the infinitesimally thin layer of energetic space that surrounds the nanomaterials. This idea could serve as the basis for table-top X-ray sources. Credit: Nicholas Rivera, adapted from Nat. Phys. 15, 1284–1289 (2019).