At the heart of modern quantum computers is a deceptively simple structure: the Josephson junction.
Traditionally, this device is formed by placing two superconductors on either side of an ultrathin barrier. Despite their separation, superconducting electrons can act in unison and conduct electrical current with amazing precision and no loss of energy.
This synchronous behavior underpins today’s most advanced quantum processors, and related advances were recognized at the highest level when they won the 2025 Nobel Prize in Physics.
Now, an international team of physicists has published a report that casts doubt on a long-held blueprint. In a new study, researchers have provided the first experimental evidence that Josephson junction-like behavior can emerge even in the presence of just one true superconductor.
Devices that shouldn’t work do work
In the new experiment, scientists constructed layered structures made of superconducting vanadium and ferromagnetic iron, separated by thin insulating layers of magnesium oxide.
Conventional wisdom suggests that this setup should not behave like a Josephson junction. Iron is not a superconductor, and its ferromagnetism usually suppresses the delicate electron pairs needed for superconductivity.
However, electrical measurements revealed a different story. The research team observed a current pattern that closely matches that of a conventional Josephson junction.
Somehow, the superconducting behavior from the vanadium crossed the barrier and reorganized the electrons inside the iron strongly enough to create synchronous motion between the two materials.
This finding confirms a long-standing theoretical prediction that has never been experimentally demonstrated before.
hear the noise
Important evidence came from analysis of electrical “noise”. Although current appears smooth on a macroscopic scale, it is actually made up of discrete electrons arriving in rapid bursts.
The statistical patterns of these fluctuations reveal how the electrons move and whether they operate independently or in coordinated groups.
In vanadium-iron devices, noise measurements reveal that electrons move in large synchronized packets within the iron layer.
This collective motion is characteristic of Josephson junctions and is a strong indicator that superconducting correlations have taken hold in unexpected locations.
The encounter between magnetism and superconductivity
What is particularly shocking about this discovery is the role of iron.
Superconductivity typically relies on pairs of electrons with opposite spins, whereas ferromagnets like iron prefer electrons aligned in the same direction. These opposing tendencies are usually irreconcilable.
The experiment suggests that iron has developed a different and unconventional form of superconductivity, involving pairs of electrons with the same spin.
Even more remarkable, this induced state was robust enough to communicate across the barrier, effectively coupling with the vanadium as if both sides were superconductors.
Impact on quantum technology
If this single superconductor Josephson junction is identified and improved, it could have far-reaching implications.
From a design perspective, reducing the number of superconducting components needed could simplify manufacturing and expand material options for quantum circuits.
The results could also have implications for research into topological superconductors, which are highly valued for their resistance to environmental noise, a major hurdle in quantum computing.
Pairing of like spins can help stabilize the quantum information encoded in the electron spins, making qubits more reliable.
From the lab to real-world devices
Another interesting point is practicality. Iron and magnesium oxide are already widely used in commercial technologies such as hard drives and magnetic random access memory.
Adding superconducting elements could enable hybrid devices that combine quantum functionality with existing manufacturing techniques.
Although questions remain about the exact mechanisms at work, this study opens a new chapter in Josephson junction research.
By showing that superconducting synchronization can occur in unexpected places, scientists may have discovered a simpler and more versatile path toward the next generation of quantum computers.
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