15 March 2024
A major challenge in building a quantum computer is its scalability, i.e. the ability to connect millions of qubits. In contrast to semiconductor chips in conventional computers, quantum chips cannot simply be enlarged. Researchers from the JARA cooperation between Forschungszentrum Jülich and RWTH Aachen University as well as the Polish Academy of Sciences were able to make progress compared to previous demonstrations using the electron shuttle method. The results were published in Nature Communications.
In quantum chips, qubits are typically closely spaced to enable coupling. However, in a scalable architecture with a large number of qubits, this is only feasible to a limited extent. To accommodate supply lines and control electronics, additional space must be created on the quantum chip. One solution is to use an electron shuttle to bridge larger distances between semiconductor qubits.
In semiconductor qubits, quantum information is encoded via the spin of electrons located in so-called quantum dots - special semiconductor structures in the nanometer range. The electron shuttle makes it possible to capture electrons on the quantum dots and transport them in a controlled manner without losing the quantum information.
Previous demonstrations have shown that single electrons can be transported short distances using an electron shuttle. The present study investigates the spin entanglement of an electron-spin pair that is separated and later reconnected to determine how long the quantum states are maintained. The shuttle speed was improved by four orders of magnitude compared to previous demonstrations. The coherence of the qubits is surprisingly maintained for longer when an electron is moved over longer distances. This is because external disturbances, which would normally reduce the coherence, can be averaged out over time. As a result, the negative effects partially cancel each other out.
Quantum computers have the potential to solve problems that even the fastest supercomputers cannot calculate. In many areas of science, architectures with thousands, if not millions, of qubits are required for quantum computers to have any practical use. The current study shows that integrating an electron shuttle into scalable semiconductor architectures is a promising approach. This approach has the advantage of being compatible with the industrial gate production of classic computer chips, which also consist of semiconductors. These findings can be used to build a functional prototype with semiconductor qubits.
Struck, T., Volmer, M., Visser, L. et al.
Spin-EPR-pair separation by conveyor-mode single electron shuttling in Si/SiGe. Nat Commun 15, 1325 (2024). https://doi.org/10.1038/s41467-024-45583-7
Group leader Silicon Quantum Technology
Communication and Outreach / Quantum Computing Focus
