DOE selects physicists from W&M to solve critical component of quantum computing


  • A team of theoretical quantum physicists from William & Mary have partnered with materials scientists to develop a new tool to solve one of the main obstacles on the way to quantum computing. Left to right: Graduate students Joseph Cuozzo, Trey Anderson, Jaeyeong Lee and Associate Professor of Physics Enrico Rossi.
    Photo by Stephen Salpukas

by Adrienne Bérard

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December 17, 2021

Computers and sensors of the future are designed one atom at a time. A team of theoretical quantum physicists from William & Mary have partnered with materials scientists to develop a new tool to harness the power of subatomic conductivity.

“Our role as theoretical physicists is to think about how to choose the different parameters of an experiment,” said Enrico Rossi, associate professor of physics at William & Mary, who heads one of the two theory groups. the condensed matter of the university.s. “In this case, we wanted to know how to tune a nanoscale device to be basically in a state where its state of superconductivity makes it a very sensitive sensor.”

The project, carried out in collaboration with materials scientists Wei Pan of Sandia National Laboratories and Javad Shabani of New York University, aims to overcome a major obstacle on the way to a more advanced quantum computer – the development of structures of type sensor capable of encoding a quantum bit, the equivalent of ones and zeros used in today’s binary computer language.

Rossi’s collaboration was one of 29 projects recently selected by the U.S. Department of Energy to receive a portion of $ 73 million in funding to advance quantum information science (QIS) research to develop the next generation of quantum smart devices and quantum computing technology.

“Quantum science represents the next technological revolution and the next frontier in the information age, and America is at the forefront,” US Secretary of Energy Jennifer Granholm said in a statement. “At DOE, we are investing in basic research, led by universities and our national laboratories, that will improve our resilience in the face of growing cyber threats and climate disasters, paving the way for a cleaner and safer future. “

Solving the world’s biggest problems starts small – very small. Rossi explained that his team is developing a theory for the semiconductor-based technology that their collaborators at NYU and Sandia are able to build at the scale of a single atom.

“They’re using what’s called molecular beam epitaxy and that means they’re growing this material one atom at a time in a perfectly clean environment,” Rossi said. “By doing this, they can control the thickness very carefully and ensure that there are no impurities entering and interfering with the structure.”

The ultimate goal is to have the structure so sensitive to interference that a single photon will trigger it, Rossi explained. The end product will be what is called a topological superconducting device, a specific combination of superconductors and semiconductors superimposed in such a way that the slightest interference – for example, a single photon – will push the structure into a topological superconducting state.

“We need the material to be extremely close to a transition from being a normal superconductor to a topological superconductor,” Rossi said. “When they’re so close to that transition, they’re very sensitive to external disturbances, which means they function like sensors. On the other hand, a system firmly in the topological superconducting phase can be very impervious to external disturbances, which makes it ideal for achieving robust quantum bits ”.

Rossi likens the material to a bag of supercooled water. When the water is clean enough, it can be carefully cooled below the normal freezing point. It is at freezing temperature, but remains liquid.

“It’s very unstable, very ready to get all icy,” said Rossi. “In fact, if you put down a single grain of salt, the molecules immediately nucleate and there is instant crystallization. It suddenly turns to ice.

He explained that a system that is just on the verge of transitioning from one state to another is a great way to monitor changes in an environment.

“In our situation, we think we can tune the system to be very close to the transition from being a normal superconductor to a topological superconductor – so close in fact that an external photon can basically drive the system into another. phase, ”Rossi said. .

Rossi explained that the team’s device will be able to detect slight changes in the electromagnetic field, allowing the development of telescopes capable of detecting light that is no longer visible or more powerful EEGs, capable of detecting abnormalities. in brain waves by detecting single neurons.

“Let’s say you have a radio that’s really far from the output source,” Rossi said. “If you can’t pick up the radio waves, then you can’t listen to them anymore. But if you have a very sensitive radio, you can keep moving hundreds of miles from the source and still listen to those radio waves, even if they are very, very weak. This is what we do with this device.

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