Josephson junctions — quantum computing building blocks — are possible with only one superconductor, experiment confirms

BUFFALO, N.Y. — Separate two superconductors with a thin layer of material and something strange happens.

Their superconductivity — a property driven by paired electrons that allows electricity to flow without energy loss — can leak into the barrier and link together, synchronizing their behavior despite the separation.

This device is known as a Josephson junction. It’s the foundational building block of quantum computers and advances of it won the 2025 Nobel Prize in Physics.

But what if a Josephson junction could function with only one superconductor — potentially opening new possibilities for simpler and more flexible quantum computing designs?

An international team has obtained the first-ever experimental evidence of exactly that, measuring electrical behavior that mimics a Josephson junction with two superconductors even though only one was present.

Their results, published in Nature Communications, suggest that the superconducting metal vanadium leaked superconducting behavior across a barrier and induced electron pairing — a hallmark of superconductivity — in the iron on the other side.

While superconductors are known to induce weak superconducting behavior in nearby materials, the iron’s induced behavior was strong enough to produce Josephson junction-like synchronization between it and the vanadium.

“A typical Josephson junction with two superconductors is like two army battalions marching in step along opposite banks of a river. In our experiment, there was only one battalion — yet it’s as if its marching caused citizens on the other side to form a militia and begin marching to the beat of a different drum,” says the study’s co-corresponding author, Igor Žutić, SUNY Distinguished Professor in the Department of Physics in the University at Buffalo College of Arts and Sciences.

The experiments — which confirmed decades-old theories — were conducted in the lab of co-corresponding author Farkhad Aliev, PhD, professor of condensed matter physics at the Autonomous University of Madrid (Spain). Other collaborators include Comillas Pontifical University (Spain), the University of Lorraine (France), the Babeș-Bolyai University (Romania) and the Eastern Institute for Advanced Study (China).

The study was supported by the U.S. Department of Energy’s Office of Science Basic Energy Sciences.

Turn on a faucet and the water appears to flow smoothly. Zoom in close enough, and that steady stream breaks down into individual droplets.

Electricity is similar. What seems to be a continuous current is actually made up of individual electrons arriving in tiny bursts.

“These small, unavoidable fluctuations in electron flow are called noise, and by listening to them we can learn how charge moves through a material,” says Jong Han, PhD, professor in the UB Department of Physics and a co-author of the study.

Analyzing noise is how the team observed Josephson junction-like behavior in their device made of vanadium and iron separated by a thin layer of magnesium oxide. The measurements revealed electrons moving in large, highly coordinated groups inside the iron — a hallmark of the synchronized behavior normally seen only when two superconducting materials are linked in a Josephson junction.

This was highly unexpected because iron is a ferromagnet, and ferromagnetism and superconductivity normally work against each other. Superconductors’ paired electrons have spins in opposite directions from each other — one up and one down — while electrons in ferromagnets mostly have spins along the same direction. An electron’s spin is like a tiny compass needle aligned with an applied magnetic field.

Yet the iron was somehow able to make superconducting pairs out of electrons with spins in the same direction.

“The iron essentially created a different type of superconductivity from vanadium,” Žutić says. “In other words, the citizens organized in their own way but kept time well enough to march as an army and send their own rhythm back across the river.”

The researchers are theorizing how iron was able to make its same-spin electron pairs robust enough that it behaved as if it was an independent superconductor.

Still, they’re excited that same-spin electron pairing could have implications for topological superconductors, which are more tolerant to environmental disturbance. Such superconductors protect quantum information — often tied to electron spin — in a knot-like way, so disturbances to parts of the system don’t easily unravel what’s happening at the core.

“The problem with conventional quantum computers is that even small environmental changes can throw off the spin of their electrons. We want to find a way to essentially lock an electron’s spin into place, and same-spin pairing could hold some answers,” Žutić says.

Another potential advantage is that a Josephson junction could be made in the future with fairly ordinary materials — both iron and magnesium oxide are widely used in commercially available magnetic computer hard drives and magnetic random-access memory.

“We have added a superconducting twist to commercially viable devices,” Žutić says.