Helium's unexpected behavior offers promising platform for qubits

Portrait of researcher Stephen Lyon in the laboratory — Stephen Lyon. Photo by Sameer A. Khan/Fotobuddy

Helium is best known for making balloons buoyant. This second lightest and second most abundant element in the universe (after hydrogen) also has a high-tech side: It’s integral to manufacturing fiber-optic cables and semiconductors, and could be key to creating a new kind of quantum computer.

When cooled to a temperature close to absolute zero (−273.15 degrees Celsius, or −459.67 Fahrenheit), helium behaves as a superfluid. “It’s an amazingly interesting material,” said Stephen Lyon, a professor of electrical and computer engineering. “A superfluid can flow without viscosity. Stir it, and it’ll just keep going forever.”

In this state, first discovered in the laboratory in the 1930s, helium atoms are “entirely governed by quantum mechanics, so you get a bunch of rather unexpected behavior,” said Lyon.

In the basement of Princeton’s Engineering Quadrangle, Lyon’s research group pumps superfluid helium into a vacuum-tight box, where it coats the surface of a silicon chip lined with precisely etched channels, but free of the wire pathways that direct electrons on a typical computer chip.

“An electron inside of a silicon semiconductor will get trapped — it’ll just get stuck,” said Lyon. “The superfluid helium gives us a surface where we can hold the electrons, but they can move across it very freely.”

This translates to long decoherence times, meaning that the spin of an electron — the property that allows it to function as a qubit in a computer — could preserve quantum information long enough to perform computations. Lyon estimates that electrons on superfluid helium could preserve their spin coherence for as long as 10 seconds — about a million times longer than mobile electrons in a silicon chip. His research team is now searching for the best conditions to measure and maximize a qubit’s coherence time in the superfluid helium system.

Building a system with sufficient qubits for complex quantum computations is a critical challenge, and Lyon believes that “piggy-backing” on known silicon technology is a promising path to a large-scale quantum computer.

In 2021, he became the chief technology officer of EeroQ, a Chicago-based startup working to commercialize current electron-on-helium technologies for quantum computing. While his industry role offers a valuable perspective on research, Lyon said, his laboratory at Princeton is focused on “inventing the future of this technology.”