CQE PI Feature – Kevin O’Brien

You want to turn those photons into classical signals that you can read, that you can measure

Featured in QSEC newsletter in fall 2021

From an early age, Kevin O’Brien has been very curious about how things work. Now an assistant professor of Electrical Engineering and Computer Science, O’Brien says he was engrossed in the “science of everyday life” as a child, whether that meant exploring the biological processes going on in the pond at his childhood home in Indiana or studying radios and televisions by disassembling them.

“My parents always give me a hard time because when I was in grade school, I would take things apart, but only after a few more years could I put them back together,” O’Brien says. “We had all sorts of disassembled TVs and radios for a while there.”

In the years after O’Brien reassembled his family’s electrical appliances, he decided that studying physics best satisfied his boundless curiosity.

“With physics, you can understand things at their most basic level and build up from there,” he says. “In reality the lines between disciplines aren’t really as sharp as we expect. Chemistry involves a huge amount of physics, and biology involves a huge amount of physics and chemistry. But I think when I was younger, I wanted to study physics just because it sort of forms the basis of how we understand the world.”

O’Brien earned his PhD at the University of California, Berkeley, in nanoscale optics and nanomaterials, engineering artificial nanostructures to get new optical properties. One such property is negative refractive index, in which light moving through a material propagates backward toward its source. The research group O’Brien worked with at Berkeley, which was led by Xiang Zhang, an international renowned expert on metamaterial engineering, exploited negative indices of refraction to create the much-heralded “invisibility cloak.”

It was in 2016 at a Mexican restaurant in Berkeley that O’Brien, his housemate who was in a different research group and another graduate student happened onto the idea of using metamaterials to create better quantum-limited amplifiers.

“They were telling me about the issues they were having with these parametric amplifiers,” O’Brien says. “We realized that metamaterial concepts could solve the issues, were a viable solution to this problem. I certainly didn’t understand all of it and had to do the math and equations, but yeah, that was it.”

O’Brien then turned his attention toward quantum computing and helped realize an amplifier that is now standard, the Josephson Traveling Wave Parametric Amplifier, which is commonly used to read quantum bits.

“It was through that collaboration that I realized, wow, quantum computers are really close, they’re actually viable,” says O’Brien. “I guess that was the moment that I realized this is a really exciting field and something I want to contribute to and start a group to aid in this effort.”

O’Brien joined MIT’s Research Laboratory of Electronics in 2018 and leads the Quantum Coherent Electronics research group. The stated aim of the group is to “advance the state of the art in superconducting quantum computing, microwave quantum optics and quantum metamaterials.”

Controlling how photons behave in a quantum computer is the fundamental benefit represented to the quantum computing field by metamaterials, O’Brien says. The photons are very weak, he says, with a very small amplitude. Their behavior is very much quantum mechanical.

“But you want to talk to your quantum computer. You want to turn those photons into classical signals that you can read, that you can measure,” O’Brien says. Low-noise or quantum-limited amplifiers “improve the quantum efficiency, making sure you don’t lose any of those precious photons that you want to amplify.”

Although O’Brien allows that most of us will never use the amplifiers in everyday life, because they have to be cooled to near absolute zero to work, he feels satisfied that they have so much scientific potential.

“I also love working on things that have applications where it can actually change something for the better,” he says.

Not only are the amplifiers used in many quantum computing experiments, even at companies like Google and IBM, O’Brien says, they are also being investigated for use as dark matter detectors.

“Amplifying very weak electromagnetic signals without adding much noise is something that is probably applicable to a lot of different areas of research,” he says.

O’Brien ponders the possibilities, even as he bicycles around Boston or is home cooking exotic meals. Rather than having a particular time or place when he does his best thinking, O’Brien says some of his research questions simply run in the background while he is engaged in his everyday activities.

“Real physics and engineering, it’s not just abstractly thinking about things. It’s also doing the work, doing the coding and experiments,” he says. “But I think there’s some quote by Feynman that you want to have the problems that are important to you in the back of your mind. Periodically, you’ll get insights.”

As a teacher and a mentor, O’Brien encourages the same kind of curiosity and questioning that he has enjoyed. He tells his students to speak up and participate without concern for any kind of hierarchical structure and meets with the students in his research group every week individually and as a group.

“I try to make it very clear that they should always speak their mind, always ask questions,” O’Brien says. “If they think something is wrong or if they think we’re not taking the right path on something, then I tell them, please talk about it.”

He says he has found that kind of collaboration throughout his experience at MIT.

“You hear rumors that MIT is like a really hardcore place. But, you know, when I interviewed and when I got here, I was blown away by how collaborative and friendly everyone is. We all want to work hard and do the best work we can, but it really is quite collaborative.”

When O’Brien’s students are feeling stumped by a problem, he passes on advice he was given by one of his postdoc mentors—advice that probably resonates with his lifelong devotion to learning how things work. “You might spend a lot of time and work very hard on this,” he tells his students, “but eventually it’s going to make sense. In the end, science works. And we might not understand it right now, but we will figure it out.”