Shinsei Ryu: Error-free quantum calculations

Shinsei Ryu, 37
Univ. of Illinois at Urbana-Champaign | Quantum Physics
Graduate school: University of Tokyo

On the boundary between the quantum and everyday realms, things don’t always make a whole lot of sense. The bundles of particles that make up materials behave in ways both unexpected and unexplained. This is the weird world that theoretical physicist Shinsei Ryu hopes to bring into focus.

Ryu ponders materials beyond the scope of classical physics at the University of Illinois at Urbana-Champaign. His research into quantum materials such as high-temperature superconductors could one day help quantum computers make error-free calculations.

Ryu’s first steps into physics weren’t entirely his own. While enrolled in the University of Tokyo, he chose physics as his major mostly because his college friends had. Since then, he’s the only one of his friends who has never considered quitting. The excitement and mysteries of the field keep him going, he says.

In 2005, when he moved to the United States from his native Japan for a postdoctoral appointment, Ryu expected to stay “for only a few years.” He quickly fell in love with the collaborative atmosphere and decided to continue his quantum career stateside.

In the materials Ryu studies, packs of electrons interact in surprising and bizarre ways. These interactions can create entirely new material properties such as superconductivity, in which electrons pair off and crowd into the least energetic quantum states instead of spreading out. The systems can be so complex that the goal isn’t finding the right answers, Ryu says, “it’s asking the right questions.” Quantum applications such as computers rely on consistency — the same question should yield the same answer every time. But the quantum interactions between electrons are often unpredictable, so Ryu hunts for measurements that reliably return the same value again and again. He likens the systems to a doughnut shape. The curvature of the doughnut’s surface can change when external forces press in, but the number of holes in the doughnut stays the same. These kinds of robust properties will make accurate quantum computing possible, he says.

The work can be very abstract and difficult at times, Ryu admits. At those points he leans on his background in experimental physics to stay grounded and “maintain a sense of reality.”

“I’m lucky,” he says. “I’ve had experience in multiple disciplines of physics. There’s no magic to this, it’s just experience.”