Scientists realize first hybrid qubit based on topological insulator

Topological qubits, with their excellent properties, are helping to make breakthroughs in the development of quantum computers designed for general-purpose applications. So far, no one has managed to unequivocally demonstrate such qubits in the laboratory. However, scientists from the Forschungszentrum Jülich in Germany have now achieved this to some extent. They have successfully integrated topological insulators into conventional superconducting qubits for the first time. Just in time for World Quantum Day on April 14, their new hybrid qubit was featured on the cover of the latest issue of Nano Letters [1].

科学家实现第一个基于拓扑绝缘体的混合量子比特

Cover of Nano Letters

Quantum computers are considered the computers of the future. Using quantum effects, they promise to provide solutions to highly complex problems that conventional computers cannot handle on realistic timescales.

However, widespread use of such computers is still a long way off. Current quantum computers typically contain only a small number of qubits. The main problem is that they are very error-prone. The larger the system, the harder it is to completely isolate it from the environment.

So much hope is pinned on a new type of qubit -- the topological qubit. Several research groups, as well as companies such as Microsoft, are taking this approach. This type of qubit has the special feature of topological protection; the special geometry of superconductors and their special electronic material properties ensure that quantum information is preserved. Therefore, topological qubits are considered to be extremely robust and largely immune to external decoherence sources. They also appear to be able to achieve fast switching times comparable to the conventional superconducting qubits Google and IBM use in current quantum processors.

However, it is unclear whether we can successfully make topological qubits. This is because a suitable material base is still lacking to experimentally generate the special quasiparticles required for this process. These quasiparticles are also known as Majorana states. So far, they have only been definitively demonstrated theoretically, not experimentally.

New possibilities are being opened up in this field thanks to the first construction of a hybrid qubit by a research team led by Dr. Peter Schüffelgen from the PGI-9 Institute at the Jülich Research Centre. They already contain topological materials at key points. This new type of hybrid qubit thus provides researchers with a new experimental platform to test the behavior of topological materials in highly sensitive quantum circuits.

科学家实现第一个基于拓扑绝缘体的混合量子比特

Hybrid qubit chip at the Jülich Research Centre

In the paper, the researchers used ultra-high vacuum manufacturing technology, realizing superconducting transmon qubit with

科学家实现第一个基于拓扑绝缘体的混合量子比特

topological insulator (TI) Josephson junction (JJ). On the substrate, microwave losses contain monolithically integrated hardmasks for selective region growth of TI nanostructures, implying microsecond limits on relaxation times, so they have the advantage of strongly coupled cavity quantum electrodynamics (cQED) compatibility.

Using cavity-qubit interactions, the researchers demonstrate that the Josephson energy of a TI-based transmon varies with its JJ size, and demonstrate qubit control and temporal quantum coherence. Their results pave the way for further studies of topological materials in novel Josephson qubits and topological qubits.

科学家实现第一个基于拓扑绝缘体的混合量子比特