When magnetic fields enter superconductors, they form tiny swirling structures known as magnetic vortices. Researchers have long regarded these vortices as unwanted disruptions that reduce the efficiency of superconductors.
In recent experiments, scientists at the Karlsruhe Institute of Technology demonstrated a new behavior in thin films of granular aluminum, a material positioned near the transition between superconducting and insulating states. Granular aluminum consists of nanoscale superconducting islands separated by non-superconducting areas. This structure creates a complex energy landscape in which vortices can settle into stable positions. The vortices can switch between these positions through quantum tunneling, a process in which particles move through energy barriers that would normally stop them.
From disruption to resource
The study shows that these vortices act as two-level quantum systems, comparable to artificial atoms with two distinguishable states. Using microwave techniques, the researchers were able to control the vortices and read out their quantum states. The coherence times, which measure how long the quantum information remains stable before degrading, reached the microsecond range. This performance is similar to that of established superconducting qubits. Qubits serve as the basic units of information in quantum computers, capable of representing multiple states at once unlike ordinary bits.
The results indicate that vortices can function as qubits in quantum technologies. “Our results show that vortices are not only controllable, but also behave just like artificial atoms with two clearly distinguishable states,” say the researchers.
Potential applications include quantum computers, highly sensitive sensors, and new methods to investigate material properties. The discovery illustrates how phenomena previously seen as problems can become useful resources when studied in the right materials. Although questions about large-scale implementation remain, the work provides promising directions for developing future quantum devices based on natural material properties.
The researchers have described the methods and results of this study in a paper published in Nature.