Eden Figueroa has long been fascinated with quantum mechanics.
It’s a strange, Star Trek-like world in which objects can exist in two or more states simultaneously, interact with each other instantly over long distances, and flash into and out of existence. Scientists like Figueroa — the quantum information technology research leader in the Department of Physics and Astronomy at Stony Brook University — work to harness this behavior with hopes of turning it into a new and improved internet.
“I think the internet is one of the greatest things humanity has ever made. But it’s not perfect,” Figueroa said. “What we want is an internet that’s fast and secure. Those are the two questions that there are currently no answers to.”
Despite the high level of the physics involved, the premise of the real-world challenge isn’t any deeper than that.
“When you have Zoom meetings you don’t want to lose the other participants, and if you’re using your credit cards for internet transactions, you don’t want people to get your information,” said Figueroa. “These are examples anyone can relate to.”
Technology is usually grown incrementally and organically; it starts off small and grows. That didn’t happen with the internet.
“In a short period of time we went from having a small network of researchers to a worldwide network in which everybody is connected,” explained Figueroa. “It was amazing and it changed the world. But nobody was paying attention along the way to things like internet security or transferring amounts of data that were previously unimaginable.”
While a standard computer handles digital bits of 0s and 1s, quantum computers use quantum bits that can take on any value between 0 and 1. And if you entangle the bits, you can solve problems that typical computers cannot. Figueroa says the main challenge to building these quantum networks is demonstrating that they work with single photons, and showing you can transfer entanglement in a network, using it whenever you need.
“If you have entanglement, you have quantum teleportation, and therefore you can move information from one place to the other,” he said. “If you manage to have lots of photons that are all entangled, then you can — in principle, using quantum teleportation — transfer lots of data from one place to the other. Once we get that far, the challenge is to transfer these entangled photons over longer distances.”
Figueroa came to Stony Brook in 2013, the first professor hired to specifically do quantum information science, tasked with building both a lab and a program. Eight years later, Figueroa and his team of 12 graduate students and two undergrads aim to develop and implement the first agnostic quantum repeater network.
“All the technology that we develop in this laboratory is intended to create a first version of that quantum repeater,” he said.
The test bed for his ideas is a quantum network connecting locations in Stony Brook and Brookhaven National Laboratory (BNL), about 17 miles away. Figueroa used existing fiberoptic infrastructure and has deployed entanglement sources and quantum memories in several buildings on the BNL campus, with fibers used to quantum connect the physics and instrumentation buildings with the Scientific Data and Computation Center. A similar local area quantum network was developed on the Stony Brook campus.
With the quantum communication channels in place, Figueroa uses the photonic entanglement sources to simultaneously store and retrieve quantum correlations in four quantum memories on both campuses. In 2020, the team achieved transmission of single-photon level polarization quantum bits (qubits) in a configuration covering a total of approximately 87 miles. This marked the longest successful quantum communication link experiment in the United States.
“In the last two or three years the problem has become bigger,” said Figueroa. “Now we have some ‘toys’; how do we network them? This is what makes us unique. With these test beds we are really testing the devices in this network configurations, and really moving quantum information over longer distances. That is very original. In the U.S. there are only a few test beds, but I think the one that we have is by far the most advanced right now.”
Figueroa isn’t alone in working toward this grand vision. His small but extremely dedicated team shares his passion, doing whatever it takes to further the cause. To illustrate the point, Figueroa shows off a working model network in his lab, with optical tables built with components that had to be made and assembled and precisely placed. “Once you build all of them, you have to align them to serve a purpose,” he said. “It’s a lot of work.”
PhD candidate Guadong Cui ’22 is on that team, and describes the quantum challenge as one of “depth and prosperity.”
“If you ask a serious thinker about it, entanglement is simply impossible — it’s like working with a ghost except that a ghost would have been much easier to understand,” said Cui. “Yet it is possible, because we generate, process and even build a quantum gate for it. The fact that I’m working on a project that hits both the deepest curiosity of me as a person and serves the need for revolutionizing information technology for human beings makes this work incredibly interesting.”
“What I like about quantum communication is that fundamental questions about light matter interaction are being studied in parallel with the engineering strategies to converge to the goal of building future technology,” added PhD candidate Sonali Gera ‘21.
Physics major Leonardo Castillo Veneros ’22, focuses on room-temperature quantum memories and finding their optimal regimes of operation.
“Before enrolling at Stony Brook, about four years ago, I visited the Quantum Information Laboratory on a campus tour and I was blown away looking at the setups on the optical tables,” said Castillo Veneros, who enrolled in Fall 2017 and began working in the lab in Spring 2018.
Rishikesh Gokhale ’25 works on developing free space quantum communication channel between BNL and Stony Brook. “I like the fact that I work on something which would replace a major chunk of the existing communication network and make communication more secure and faster,” said Gokhale, who is pursuing a PhD in physics. “I was interested in the growing field of quantum information and at the same time, I wanted to be an experimentalist. Professor Figueroa’s lab gives me an opportunity to do that.”
All team members credit Figueroa for being able to offer guidance while still allowing them to explore their individual interests within the project. Rishikesh adds that Figueroa provides the “freedom to think, implement and improvise.”
“His passion and dedication to the field are incredibly inspiring and motivating,” said Castillo Veneros. “When I first learned about the kind of work he was doing, I wanted to become part of it. I’m thankful for the opportunity to contribute to this extraordinary effort to build a quantum network on Long Island.”
As the project moves ahead, Figueroa hesitates to put a time frame on it, noting that no advancement is ever a sure thing.
“If we had unlimited funds, which is never the case, I would say the horizon is somewhere around five years from now,” he said. “With our current funding it’s going to be more like 10 years. We still need to test this network configuration and every single part of it to get it right. When we get there, then we can scale that up. But this is groundbreaking research we’re doing right now, and we’re training the leaders of the future in this area. It’s a unique story for Stony Brook. And I like that.”
— Robert Emproto