May 8, 2026
Kyle Lin
UChicago physics PhD student uses games to explain complex concepts
Shock runs through the crowd of high school students as light appears where it shouldn’t. When two polarized filters, the same material used to make sunglasses, are stacked, they block the light entirely. Somehow, when a third polarized filter is added, the light returns. The Chicago middle and high school students are mystified at what looks to be impossible. Their workshop leader, Robert Weinbaum, smiles, asking the students to ponder and discuss how that could happen.
The students are participating in ChiTech Discovery Days, a single-day field trip experience designed to generate interest in tech for middle and high school students in Chicago Public Schools, hosted by Discovery Partners Institute, part of UIUC’s Grainger College of Engineering. They are armed with the knowledge to solve this mystery of quantum physics because earlier that day, they played a game of Quantum Tic-Tac-Toe.
Quantum Tic-Tac-Toe was invented by Weinbaum, a PhD student at the University of Chicago in the Department of Physics and the Enrico Fermi Institute, and debuted at last year’s ChiTech Discovery Days.
Weinbaum studies quantum field theory and general relativity as a theoretical physicist in Robert Wald’s research group. He describes his research as fitting into two broad categories: the first involves the exploration of how quantum effects change our understanding of gravity, and the second is trying to position our existing understanding of quantum physics on firmer mathematical ground. “Physicists know how to calculate a lot of things in quantum field theory, but we don’t always understand why our techniques actually produce the right answer.” He’s interested in developing more rigorous techniques to predict quantum behavior.
Weinbaum designed Quantum Tic-Tac-Toe to introduce quantum ideas of superposition through play rather than a slideshow filled with equations. His goal was to break down the mental barrier students have when approaching complex scientific ideas. “Having something hands-on, that students can actually play with, goes a long way,” Weinbaum said.
Quantum physics is a notoriously complicated and mystified field. The media positions the subject as a topic only geniuses will ever understand. Weinbaum remembers starting at the same place as all of these students, not knowing anything about quantum physics and being confused. The demonstrations are designed not only to build confidence but to revel in learning, the process of unraveling confusion.
“I just want students to be comfortable with that, because I think an important part of going through the process of understanding quantum is to become more comfortable with confusion,” Weinbaum said.
He always starts the lesson by playing a regular game of tic-tac-toe. “The game is intuitive, but there’s always a chance that one student hasn’t played before, and then they get lost in the whole activity,” said Weinbaum.
Only then does he introduce quantum mechanics. In traditional tic-tac-toe, the tiles are certain during play; an X is always an X, and an O is always an O. In the quantum version, Weinbaum introduces the quantum concept of superposition, the idea that something can exist in multiple states at once. These states are represented by pieces marked with both X and O symbols, indicating to students that the piece can become either an X or an O. Only after a student uses the superpositioned piece and measures by spinning a wheel is its identity fixed.
The process mimics observation in quantum mechanics, where something chooses its state only when it is measured; in the game, the measurement is modeled by spinning the wheel. “When the piece is played, we don’t immediately know what it will be,” Weinbaum said. “Only when we spin the wheel does the state collapse into an X or an O.” In this second round of tic-tac-toe, the superpositioned pieces have a 50/50 chance to be either X or O.
However, Weinbaum takes it a step further with a third iteration, introducing weighted superposition, with pieces that lean more heavily toward X or O. Weighted superposition is generally avoided in public lessons and mass media because it's less intuitive to understand. “Everyone has an intuition of a coin flip being 50/50, but the unequal probabilities in weighted superposition mean people have to remember their fractions and get bogged down in the weeds,” said Weinbaum. “But when you're working with a wheel that shows this piece has more of X and less of O, it becomes easy to follow.”
Weinbaum originally started his science outreach during his undergraduate career at the University of Michigan, where he joined the STEM Society. “I initially got involved because I wanted to show people what I thought was cool in science, so I guess that’s a little selfish,” said Weinbaum. “But then, as I did it more, I saw the impact of those moments when people see my demonstrations and want to learn more and consider it for their future. Over time, those moments became their own reward, and I began chasing that feeling of helping others discover.”
That motivation is what led Weinbaum to reach out to the ChiTech Discovery team. He realized the feeling of helping others had become ingrained within him; his goals for outreach evolved to helping students see themselves in science. Weinbaum explained that students aren’t always given the same exposure, particularly students from underrepresented backgrounds who aren’t able to see people who look like them in science. It's a twofold problem; both their lack of experience and lack of role models mean they might not consider science as a career, or worse, they consider themselves unsuitable for science.
“I design my lessons to reflect a component of what real science entails, to be able to articulate, for example, that as eighth graders, you already did something a real scientist would do, which gives them confidence to consider a career in science,” said Weinbaum. That is particularly important, Weinbaum notes, because Chicago, where these students are growing up, is an epicenter of quantum technology both in America and the world.
Weinbaum watches the discussion occur in the classroom around him, as students get closer and closer to explaining the polarized filter phenomenon.
In this case, light is a wave that can oscillate in any direction: vertically, horizontally, or at an angle between. Each filter blocks light waves in a particular direction. When it meets the first filter, which lets through vertical light waves, some of the light is blocked, and only the vertical light is allowed through. Since the second filter is diagonal, the vertical light has a 50/50 chance of making it past, which we see as the light having a reduced intensity. In that process, the light becomes diagonally oscillating.
Finally, the last filter allows through only horizontal light waves, but what happens when the light hitting it is diagonal? The diagonal light can be thought of as a superposition of vertical and horizontal oscillations. So the third filter can be thought of as spinning the probability wheel, choosing to see the light as vertical or horizontal, X or O. Without the middle filter, this would be impossible, as the first filter would cause all the light passing through to be vertical, and none of the light would pass through the second horizontal filter.
While Weinbaum rarely sees these students after his lessons, Kay Monelle, the K-12 program director who oversees ChiTech Discover Days, notes the impact of these demonstrations: “Teachers have sent us emails saying the students were super excited, they got back to the school, and they wanted to talk more about quantum. I’ve seen Robert in action, and he’s a wonderful teacher. There’s a space for him as an educator.”