Physicists move one step closer to topological quantum computing

A team of experimental physicists led by the University of Cologne have shown that it is possible to create superconducting effects in special materials known for their unique edge-only electrical properties. This discovery provides a new way to explore advanced quantum states that could be crucial for the development of stable and efficient quantum computers.

Their study, titled “Induced Superconducting Correlations in an Anomalous Quantum Hall Insulator,” is published in Nature Physics.

Superconductivity is a phenomenon where electricity flows without resistance in certain materials. The anomalous quantum Hall effect is another phenomenon that also causes zero resistance, but with a twist: it’s confined to the edges instead of spreading throughout.

The theory predicts that a combination of superconductivity and the anomalous quantum Hall effect will create topologically protected particles called Majorana fermions that will potentially revolutionize future technologies such as quantum computers.

Such a combination can be achieved by inducing superconductivity at the edge of an anomalous quantum Hall insulator that is already resistance-free. The resulting Majorana chiral edge state, which is a special type of Majorana fermions, is a key to realizing “flying qubits” (or quantum bits) that are topologically protected.

Anjana Uday, a final year PhD researcher in the group of Professor Dr. Yoichi Ando and first author of the paper, explained: “For this study we used thin films of anomalous quantum Hall insulator contacted by a superconducting niobium electrode and tried to induce chiral Majorana states at its edges.

“After five years of hard work we finally managed to achieve this goal: When we inject an electron into one terminal of the insulating material, it is reflected back to another terminal, not as an electron but as a hole, which is essentially a ghost of an oppositely charged electron.

“We call this phenomenon cross-Andreev reflection, and it enables us to detect induced superconductivity in the topological edge state.”

Gertjan Lippertz, a postdoctoral student in the Ando group and co-first author of the paper, added, “This experiment has been attempted by many groups in the last 10 years since the discovery of the anomalous quantum Hall effect, but no one has succeeded in it. seen.

“The key to our success is that the deposition of the anomalous quantum Hall insulator film, every step of the device fabrication, as well as the ultra-low temperature measurements are all done in the same lab. This is not possible anywhere else.”

To achieve these results, the Cologne group collaborated with colleagues at KU Leuven, the University of Basel as well as the Forschungszentrum Jülich. The latter contributed theoretical support within the joint subject and light group of excellence for quantum computing (ML4Q).

“The cluster has been instrumental in providing the collaborative framework and resources needed for this progress,” elaborated Yoichi Ando, ​​Professor of Experimental Physics at the University of Cologne and spokesperson for ML4Q.

This discovery opens up numerous avenues for future research. Next steps include experiments to directly confirm the occurrence of chiral Majorana fermions and elucidate their exotic nature.

Understanding and exploiting topological superconductivity and chiral Majorana edge states could revolutionize quantum computing by providing stable qubits that are less susceptible to decoherence and information loss.

The platform demonstrated in this study offers a promising path toward achieving these goals, potentially leading to more robust and scalable quantum computers.