TU Delft and Fujitsu have developed the world’s first working prototype of a diamond-spin quantum computer incorporating tin-vacancy (SnV) centers into photonic integrated circuits.
The prototype is based on the results of joint research started in 2020 by Fujitsu, Delft University of Technology (TU Delft), and QuTech, a quantum technology research institute and part of TU Delft.
The prototype can be operated at -271.6°C, higher than the typical operating temperature of superconducting quantum computers (-273.13°C) and can be utilized via the Fujitsu Hybrid Quantum Computing Platform without any additional specialist knowledge.
This development represents an important milestone toward realizing a modular architecture, one of the most promising approaches for scaling quantum computers, due to its high fidelity and efficient optical connectivity.
“Demonstrating the scalability expected of diamond spin quantum computing remains a long and challenging journey,” said Kees Eijkel, General Director of QuTech, “However, by further strengthening our collaboration with Fujitsu, we are committed to tackling this ambitious and meaningful challenge and leading the development of next-generation quantum technologies.”
Vivek Mahajan, CTO in charge of system platform at Fujitsu, said the diamond-spin approach they applied in this prototype has the potential to be integrated with superconducting quantum computers. This will further extend their capabilities, enabling more complex and large-scale computations.
“Under our roadmap to achieve a 250 logical qubit system by fiscal 2030 and a 1,000 logical qubit system by fiscal 2035, Fujitsu will continue advancing practical quantum computing across a broad range of areas, from software to hardware, while leveraging the key advantages of the diamond-spin approach, including high fidelity and optical connectivity,” said Mahajan.
The prototype features these three technologies developed by Fujitsu. First, a heterogeneous material bonding and thinning technology for scalable quantum computing chips.
To create quantum computing chips using SnV centers, Fujitsu developed heterogeneous material bonding technology to bond high-quality diamond substrates ion-implanted with tin to alumina/silicon dioxide substrates.
Fujitsu also developed thinning technology to reduce the thickness of diamond substrates from several hundred micrometers to several hundred nanometers, making them suitable for use in quantum computing chips.
Second, photonics-integrated circuit fabrication technology for SnV centers. Fujitsu developed technology to fabricate photonics integrated circuits that integrate nanometer-sized diamond crystals containing SnV centers with alumina optical waveguides, which are transparent in the visible light region, to extract single photons emitted from SnV centers during qubit readout.
For diamond processing, Fujitsu utilized the results of joint research with The University of Tokyo.
Third, quantum circuit conversion technology for diamond spin approach, which requires qubit control by combining light, microwaves, and radio frequency waves.
Fujitsu developed a mechanism to convert quantum circuits described by quantum gates into control sequences for these physical operations for the diamond spin approach, enabling control from Fujitsu’s hybrid quantum computing platform.
The diamond-spin approach takes lattice defect structures called color centers in diamond crystals and uses them as qubits. This approach achieves high fidelity because diamond has inherent properties that allow quantum states to remain stable and could allow for logical qubits to be reliably formed from fewer physical qubits compared to superconducting and other approaches.
Furthermore, light can be applied to flexibly connect several quantum modules, enabling the construction of systems with a modular architecture that can be scaled efficiently.
Typically, the diamond-spin approach uses structures called nitrogen-vacancy (NV) centers formed by nitrogen atom impurities in diamond crystals.
However, in the development of this prototype, Fujitsu used SnV centers, which feature structural symmetry and are less susceptible to external noise than NV centers, making them attractive candidates for stable, high-brightness color centers.
