With reduced cooling needs, prolonged operational times, and lower error rates, quantum computers utilizing spin photons and diamonds present considerable benefits compared to other quantum computing technologies. The consortium involved in the BMBF project SPINNING, led by Fraunhofer IAF, has made significant strides in developing quantum computers based on spin photons. On October 22 and 23, 2024, the partners showcased the project’s interim findings during the mid-term meeting organized by the BMBF funding initiative for Quantum Computer Demonstration Setups in Berlin.
Quantum computers have the potential to resolve intricate issues in a matter of seconds that would take traditional supercomputers decades to tackle. However, while the goal seems clear, the journey to achieving it remains complex. Various competing techniques still exist for creating quantum computers, each presenting unique pros and cons relating to hardware and software, including reliability, energy use, and compatibility with existing systems.
Under the guidance of the Fraunhofer Institute for Applied Solid State Physics IAF, a collaborative effort involving 28 partners is underway for the “SPINNING — Diamond spin-photon-based quantum computer” project. This initiative aims to establish a quantum computer leveraging spin photons and diamonds, expected to require less cooling, operate longer, and exhibit fewer errors than other existing quantum computing technologies. The hybrid model of the spin-photon-based quantum computer also promises enhanced scalability and connectivity, allowing for flexible integration with traditional computers.
Qubits created through diamond color centers
“Our goal in the SPINNING project is to make a significant contribution to Germany’s quantum technology landscape. We intend to utilize diamond’s material qualities to develop a quantum computing technology that can match the capabilities of existing technologies while eliminating their specific weaknesses,” explains Prof. Dr. Rüdiger Quay, coordinator of the SPINNING network and director of Fraunhofer IAF. “We generate qubits through color centers within the diamond lattice by trapping an electron in one of four artificially created defect sites (vacancy centers) infused with nitrogen (NV), silicon and nitrogen (SiNV), germanium (GeV), or tin (SnV). The electron’s spin interacts magnetically with the nuclear spins of five neighboring 13C carbon isotopes, allowing the central electron spin to function as an addressable qubit.”
“The individual qubits are organized into a matrix structure known as a qubit register. The SPINNING quantum computer is designed to include at least two and eventually up to four of these registers, which can be optically coupled over distances, such as 20 m, to facilitate extensive information exchange,” Quay continues. The optical coupling between the central electron spins and their registers is achieved with an optical router, light source, and detector for readout. High-frequency pulse sequences control the states of the nuclear spins.
Project results: Demonstrated entangled qubit registers with high fidelity
At the mid-term meeting of the Quantum Computer Demonstration Setups funding program of the Federal Ministry of Education and Research (BMBF), which funds SPINNING, the consortium reported groundbreaking interim results on October 22 and 23, 2024, in Berlin. They showcased considerable achievements, including the first-time demonstration of entangled pairs from two registers, each containing six qubits, over a distance of 20 m, with a high mean fidelity indicative of similarity in the entangled states.
Other advancements include improvements in the core hardware and software, alongside peripheral systems for the spin-photon-based quantum computer: Enhancements in base material and processing methods, along with progress in realizing color centers in diamond for generating qubits and developing photonic resonators. This progress stems from a deeper understanding of the four types of defects in the diamond lattice and methods to reduce errors in diamond-based qubits. Additionally, the consortium has succeeded in advancing the necessary electronics for operating the quantum computer and demonstrating its initial applications in artificial intelligence.
Benefits compared to superconducting quantum computers
A comparative analysis of the interim outcomes from the SPINNING project against key metrics for quantum computers built on superconducting Josephson junctions (SJJs) highlights the significance of this work, noting that considerably more resources have been allocated globally towards SJJs. Displaying an error rate below 0.5%, the spin-photon-based quantum computer containing twelve qubits achieved comparable performance in one-qubit gates to the leading SJJ models Eagle (127 qubits) and Heron (154 qubits).
In terms of coherence time, the spin-photon-based quantum computer exceeds 10 ms, markedly surpassing the >50 µs found in SJJ models, while entanglement can occur over vastly greater distances at 20 m instead of just a few millimeters.
Future Outlook: Addressing resonator design and software development challenges
Remaining technical hurdles before completing the project include advancing the resonator design for improved consistency and precision. Additionally, researchers are focused on enhancing the software for the autonomous control of routing in the spin-photon-based quantum computer.
About the SPINNING project
The SPINNING initiative receives funding from the Federal Ministry of Education and Research (BMBF) through the Quantum Computer Demonstration Setups program, which is part of the federal government’s Quantum Technologies framework — from Fundamentals to Market. Fraunhofer IAF oversees a consortium that includes six universities, two non-profit research institutes, five industrial partners (including SMEs and spin-offs), as well as 14 affiliated partners.
- Fraunhofer Institute for Applied Solid State Physics IAF (Coordinator)
- Fraunhofer Institute for Integrated Systems and Device Technology IISB
- Research Center Jülich GmbH
- Karlsruhe Institute of Technology (KIT)
- University of Constance
- University of Heidelberg
- Technical University of Munich
- University of Ulm
- Diamond Materials GmbH, Freiburg im Breisgau
- NVision Imaging Technologies GmbH, Ulm
- Qinu GmbH, Karlsruhe
- University of Stuttgart
- Quantum Brilliance GmbH, Stuttgart
- Swabian Instruments GmbH, Stuttgart
- 14 affiliated partners from academia and industry
Discover more about the partners and their roles in the project: Project Partners
