Joel Yuen-Zhou Thinks Theory is Fun

Growing up in Mexico City, we had these competitions called Science Olympiads. I had no exposure to people who were scientists or mathematicians, but Science Olympiads gave me access to mentors who were university professors and devoted a considerable amount of time training us for competitions. They were the ones who made me aware that I could make a living out of math. School at the time was easy for me, and the idea of remaining a student indefinitely was quite appealing, especially having witnessed the long hours that my parents worked in the restaurant.

Long story short, I had a better gift for chemistry. When I was younger, I worried I was betraying my passion for mathematics by studying chemistry, but I have since realized that I can do chemistry, physics and mathematics at the same time. It is only now that I’m older that I can fully appreciate how wonderful chemistry is and feel proud contributing to a field which represents such an amazing achievement of human knowledge.

Many people think that mathematics and physics are incomprehensible subjects that don’t make any sense, but when you take your time chewing on equations, you realize they’re unveiling a story, and the story can be quite beautiful and compelling. As theorists, we are storytellers in search of those beautiful theories that hopefully provide some unifying, logical structure to a natural phenomenon.

I wouldn’t claim to practice math that is anywhere near what my colleagues in the math department do, but our bread and butter is theoretical physics and chemistry — mainly quantum mechanics, statistical mechanics, and some electromagnetism here and there. We use cute pieces of math to provide a coherent story from beginning to end, to understand the logical flow of ideas and to check for contradictions.

Q: Photons are particles representing a quantum of light or other electromagnetic radiation. You once described them as "magic wands."

I'm still mesmerized by what photons can do, and how you can use them to detect tiny features or measure very large distances. They're really versatile tools, and when you have versatile tools that are easily understood, you can become creative in their use. The question I’m asking is how can photons determine things about molecules in more precise ways or affect the course of how molecules behave?

The reason photons are understood much better than molecules is because photons obey rules that are well known through the laws of electromagnetism. Whereas molecules obey the rules of quantum mechanics, and the parameters that we are supposed to plug into these calculations are much harder to quantify.

But then it turns out that those molecules can interact with light, and because we understand light so well, we can basically tame some of these rebellious molecular behaviors. This is my program of research, essentially how to use photons in creative ways to manipulate or measure molecules. 

Why do you like most about working at UC San Diego?

I have been here for 10 years. I can finally call myself a San Diegan and I really enjoy living here. I love that there’s so much natural stimulus. The ocean and the mountains are beautiful and we must not take them for granted.

I would say UC San Diego is a forward-looking institution. It’s young and dynamic and doesn’t have the stuffy traditions or restrictive guidelines of some other places. I feel free to pursue things that I’m really interested in without boundaries. There are no restrictions on how to think about a particular problem, or that you need to be a certain type of chemist, because the type of theoretical chemistry that I do is not very traditional.

Q: Your parents are Chinese and you were born in Mexico. How have these different cultures influenced you?

I believe both cultures have strongly defined me in different ways. During my formative years in Mexico, it was often hard to fit in, being an ethnic minority and a nerdy one for that matter. But then, I always found my own path and comrades. This is why academia is great: you find strange people to talk with about strange things that you obsess about. I have always been at the crossroads of different cultures, so I am fine not being a traditional chemist or physicist, and being in between. This cosmopolitanism and interdisciplinarity are my natural habitats.

I was an ethnic minority, but I was born and raised Mexican and I am very proud of that. Mexico gave me and still gives me a lot. My deep appreciation of science and the humanities comes from an amazing education from Mexican teachers before I came to college in the U.S. My outlook in life is deeply Mexican, and so is my sense of humor. I have amazing and long-lasting Mexican friends and love the sensibility, creativity and warmth of its people.

My Chinese side obviously weighs heavily on me, starting from my looks. Embarrassingly, my biggest handicap as a Chinese is that I only have elementary conversational skills in a rural Cantonese dialect called Long Du, which is sadly at risk of extinction. I only speak it with my parents and a few relatives. However, modesty aside, I must say I understand Chinese food much better than many of my Chinese friends! While I’m not a great experimental chemist, I am a pretty good experimental cook. I guess even as a scientist, I cannot escape the family cafeteria business!