Qubits Magnetic Vortices in Superconductors As A Desired Effect

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Magnetic fields in superconductors are usually disruptive. A team of scientists involving the Karlsruhe Institute of Technology (Germany) has now developed methods to generate these magnetic fields in a targeted manner. These can serve as a step towards generating qubits, the information units for quantum computers.

Superconductors are materials that, under certain conditions, conduct electrical current without resistance and normally displace magnetic fields completely. However, if a critical magnetic field is exceeded, magnetic fields in the form of tiny, quantized vortices, also known as vortices, penetrate the material. These were previously regarded as undesirable disruptive factors, as they cause energy losses and limit the performance of superconducting systems.

The current study by Professor Ioan M. Pop's research team at the Institute of Quantum Materials and Technologies (IQMT) at KIT demonstrates a fundamentally new behavior of magnetic vortices in superconductors. The researchers investigated highly disordered superconducting thin films of granular aluminum layers near the transition between superconductivity and insulator. In this material, the vortices lose their disruptive properties and form stable, low-loss states that can be described quantum mechanically.

Vortexes Arise Due to the Material

The physical basis of this effect lies in the special structure of the material: granular aluminum consists of nanoscale superconducting islands that are connected by weak couplings. This creates a complex energy landscape with local minima, quasi energetic "troughs", between which a vortex can tunnel back and forth quantum mechanically. In this way, stable two-level systems are formed, which underlie the observed quantum states.

Our results show that magnetic vortices are not only controllable, but behave like artificial atoms with two clearly distinguishable states.

Dr. Simon Günzler, IQMT

"This means they fulfill a key requirement for use as qubits in quantum technologies," adds Pop. "At the same time, the study shows that even effects that have long been considered disruptive can become valuable resources under the right conditions. This opens up completely new perspectives for the design of future quantum systems."

The researchers were not only able to detect these vortex qubits, but also to specifically excite, control and read them out using microwave measurements and quantum electrodynamics methods. The measured coherence and relaxation times are in the microsecond range and are therefore comparable with established superconducting qubit systems. This makes vortex qubits one of the most unusual candidates for quantum technology applications to date.

Qubits No Longer Produced Artificially

In the long term, such systems could serve as new types of qubits that do not have to be artificially manufactured, but instead emerge from intrinsic material properties. In addition to potential applications in quantum information technology, new avenues are also opening up for the experimental investigation of complex materials. In future, vortex qubits could be used as sensitive probes to precisely analyze the microscopic properties of superconductors.

"Even if there are still questions about technical implementation and scalability, our results impressively show that even supposedly undesirable effects in physics can become useful quantum mechanical resources under the right conditions," says Pop. The example of superconducting vortices opens up new avenues for future technologies.

Researchers from the University of Antwerp and the University of Ulm (Germany) were also involved in the study.

Original publication: Ameya Nambisan, Simon Günzler, Dennis Rieger, Nicolas Gosling, Simon Geisert, Victor Carpentier, Nicolas Zapata, Mitchell Field, Milorad V. Milošević, Carlos A. Diaz Lopez, Ciprian Padurariu, Björn Kubala, Joachim Ankerhold, Wolfgang Wernsdorfer, Martin Spiecker & Ioan M. Pop: Quantum coherent manipulation and readout of superconducting vortex states. Nature, 2026.