Why you should care
His research may help make much-anticipated quantum computers a reality.
Growing up, Jonathan Simon loved playing Dungeons & Dragons — but not because the game involved elves, orcs or other fantastical creatures. It was all about the dice: Rolling them determined the outcome of every action. “What I thought was cool was that someone had gone through the effort of making rules to determine how a universe worked,” he says.
Now an assistant professor of physics at the University of Chicago, Simon recently tested his understanding of how the laws of nature govern our universe by pursuing a lofty question: Is it possible to make light behave like matter? In other words, could he create matter from light?
The answer: Yes. In a 2016 Nature paper, Simon described building a two-dimensional material out of photons, the tiny packets of energy that make up light, and teaching them to behave like electrons, elementary particles that make up matter. His findings mark an important step toward developing quantum computers, highly powerful machines that may one day perform calculations too unwieldy for today’s standard computers and help us tackle daunting problems — like predicting catastrophic storms or the effectiveness of a new drug — faster and more easily.
Anything that involves successfully manipulating and controlling light brings us one step closer to quantum computing.
Michael Dennin, physics professor, UC Irvine
While standard computers use electrical current to switch units of data known as bits “on” or “off,” quantum computers use subatomic particles called qubits. The massive computing power of qubits lies in their ability to be switched to more than one setting simultaneously, enabling them to juggle multiple calculations at once. Some researchers are trying to use the electrons in solid materials as qubits. But photons may have an edge. Materials made of photons are less disordered than solid materials, which can have defects or impurities, and collections of photons can also travel farther and faster as a unit than electrons.
“Anything that involves successfully manipulating and controlling light brings us one step closer to quantum computing,” says Michael Dennin, professor of physics and astronomy at the University of California, Irvine. Martin Weitz, professor of physics at the University of Bonn, calls Simon’s work “amazing.” “It has been done with electrons,” he says. But “normally you wouldn’t think the same thing could be done with light.”
But Weitz notes that while photons can travel long distances, many get lost along the way. “One feature of these photonic systems is that they’re leaky,” says Mohammad Hafezi, a fellow in the Joint Quantum Institute at the University of Maryland. “You have to constantly pump the system with photons.”
A self-professed geek, Simon, 35, looks every bit the part — from his glasses to his goofy grin — as he Skypes from a conference close to where he grew up in Chevy Chase, Maryland. As a kid, he built robots and won a spot in the prestigious Intel Science Talent Search finals.
Simon studied physics at Caltech, and later as a Ph.D. student and postdoc at Harvard. There, he harnessed the bizarre laws of quantum physics to create exotic materials that have strange properties — like graphene, an extremely strong yet flexible material only one atom thick. Relying on quantum physics, he built these materials to then study their implications. Some, for instance, could be used to make better heat and electrical conductors or faster computers. He laser-cooled atoms to model such materials and investigate the behavior of their hard-to-study electrons. But laser-cooled atoms have limitations. It’s tricky, for instance, to teach atoms to orbit and collide like electrons in a magnetic field.
So he turned to another particle: the photons that make up light. Could he teach photons to behave like electrons? Could he use them as building blocks for exotic materials?
Specifically, Simon wondered whether he could make photons act like electrons in what’s known as a quantum Hall material, a two-dimensional exotic material where only the edges conduct electricity, and only in one direction, making it less vulnerable to manufacturing defects. And because its electrons all orbit in the same direction, it represents a promising approach to quantum computing that may guard against processing errors.
Soon after joining the University of Chicago faculty in 2012, Simon got to work building a quantum Hall material, but out of photons instead of electrons. He and his team positioned four mirrors to ricochet light off each other, trapping and “twisting” it along the way. Twisting the light made the photons orbit like electrons do in a strong magnetic field; in other words, it made them move like electrons in a quantum Hall material. Simon’s team then aimed a special instrument at different regions of the material to measure the energy levels of the light that passed through it. Sure enough, the energy levels matched those of electrons in a conventional quantum Hall material.
A quantum computer that uses photons as qubits would carry out computations through collisions between the photons. Problem is, photons normally can’t interact with each other. (Need proof? Shine two flashlights at each other, Simon suggests. Spoiler alert: Nothing happens. The beams pass through each other.) According to preliminary findings, Simon’s team made photons behave as though they collided with each other by sending them through a cloud of laser-cooled atoms that continuously absorbed and re-emitted them, forming polaritons — particles that, in simple terms, are part light and part matter. They set up the experiment so the absorbed photon excited the matter parts of the polaritons so strongly that they could now collide with each other.
Simon’s next step is to build off his first study (twisting light to make photons orbit like electrons in a strong magnetic field) and make photons collide in a twisted cavity. He knows he has his work cut out for him. But the challenge summons his inner Dungeons & Dragons–playing kid. “Physics is not very forgiving,” he admits, but the thrill lies in getting “to really test how well I understand all kinds of different things.” That sense of unbridled play may very well lead to other significant surprises, no matter how the dice land.