Discover Quantum Power Hidden inside Diamonds

This innovative approach leverages the unique properties of diamonds to create stable qubits, aiming for high scalability and fidelity in quantum computing. Recent achievements include the successful demonstration of qubit entanglement over long distances, significantly outperforming traditional quantum computers in error rate and coherence time, the SciTechDaily reported.

Quantum computers promise to solve complex problems in seconds, tasks that would take modern supercomputers decades to complete. While the goal of achieving this capability is clear, the path remains uncertain due to multiple competing approaches to building quantum systems. Each approach comes with its own strengths and limitations in areas such as hardware reliability, energy efficiency, and compatibility with existing technology.

Coordinated by the Fraunhofer Institute for Applied Solid State Physics IAF, a consortium of 28 partners is developing a unique quantum computer through the “SPINNING — Diamond spin-photon-based quantum computer” project. This diamond-based, spin-photon model is expected to require less cooling, operate for longer periods, and have lower error rates than other quantum computing technologies. Its hybrid design also enhances scalability and connectivity, allowing for more flexible integration with traditional computing systems.

“In the SPINNING project, we want to make an important contribution to the German quantum technology ecosystem. To this end, we are using the material properties of diamond to develop a quantum computing technology that can be just as powerful as the other technologies but has none of their specific weaknesses. We create qubits using color centers in the diamond lattice by trapping an electron in one of four artificially created lattice defects (vacancy centers) doped with nitrogen (NV), silicon and nitrogen (SiNV), germanium (GeV) or tin (SnV). The electron spin couples through magnetic interaction with five nuclear spins of neighboring 13C carbon isotopes. The central electron spin can then be used as an addressable qubit,” explains Prof. Dr. Rüdiger Quay, coordinator of the SPINNING network and institute director at Fraunhofer IAF.

“The individual qubits form a matrix structure, the qubit register. The SPINNING quantum computer will consist of at least two and later up to four of these registers, which in turn will be optically coupled over long distances of 20 m, for example, so that a comprehensive exchange of information can take place,” Quay continues. The optical coupling between the central electron spins and registers is realized by an optical router in combination with a light source and a detector for readout. The individual states of the nuclear spins are controlled by high-frequency pulses.

On the occasion of the mid-term meeting of the funding measure Quantum Computer Demonstration Setups of the Federal Ministry of Education and Research (BMBF), under which SPINNING is funded, the consortium presented the interim project results on October 22 and 23, 2024, in Berlin. They are characterized by remarkable successes. For the first time, the project team successfully demonstrated the entanglement of two registers of six qubits each over a distance of 20 m and achieved a high mean fidelity (in the sense of the similarity of the entangled states).

Further project successes include significant improvements in the central hardware and software as well as the peripherals for the spin-photon-based quantum computer: The basic material and its processing, the realization of color centers in diamond for the generation of qubits, could be improved as well as the technology of the photonic resonators. The basis for this was a better understanding of the four types of defects in the diamond lattice and the error mitigation of diamond-based qubits. The consortium also succeeded in developing the electronics required to operate the quantum computer and demonstrating the first applications of the quantum computer for artificial intelligence.

The exemplary comparison of the interim results of SPINNING with the key indicators of quantum computers based on superconducting Josephson junctions (SJJs) underlines the value of the work done in the project as, to date, many times more resources have been invested worldwide into the latter’s development. With an error rate of < 0.5%, the spin-photon-based quantum computer comprising twelve qubits to date achieves the same result in the one-qubit gate as the prominent SJJ models Eagle (127 qubits) and Heron (154 qubits).

In terms of coherence time, the spin-photon-based quantum computer with a length of over 10 ms clearly outperforms the SSJ models (> 50 µs), although the distance for entanglement is many times greater at 20 m compared to a few millimeters.

The remaining technical challenges until the end of the project include the further development of the resonator design towards improved reproducibility and more precise alignment. On the other hand, the researchers are working on further improving the software for automatic control of the spin-photon-based quantum computer’s routing.

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