Exploring Fujitsu’s Diamond Spin ApproachCould a Diamond Become the Heart of a Quantum Computer?
Interview article | 2026-09-10
10 minute read
Hello! I’m Nao from Fujitsu’s Marketing Strategy Division.
When you hear the word “diamond,” do you think of a gemstone? Today, researchers are exploring how diamond could become a technology that supports the future of quantum computing.
Fujitsu has announced research results in diamond-spin-based quantum computing, an approach that uses deliberately created atomic-scale defects in diamond. This marks an important step toward realizing a “sixth approach,” a new option alongside the leading approaches to quantum computing.
Fujitsu is advancing research on diamond-spin-based quantum computing as a promising approach for future large-scale quantum systems. The prototype developed this time is the first module based on the diamond spin approach and represents an important milestone toward scalable quantum computing.
The newly developed system is the first prototype module based on the diamond spin approach. It is designed from the outset to connect qubits optically and scale by linking multiple modules, making it an important first step toward large-scale quantum computing.
In this article, we explain the key features of technology and introduce steps that researchers went through.
【Meet the Researchers】
Kenichi Kawaguchi: Senior Project Director overseeing the development, currently working across two locations in the Netherlands and Japan.
Ryota Kitagawa: Responsible for designing and verifying the operation of the quantum processor chip. Enjoys watching baseball and home gardening.
Itsuki Takagi: Responsible for building the measurement environment, including the optical and high-frequency systems and cryostat. Enjoys photography and reading.
Masayuki Hosoda: Responsible for building the cryostat and measurement equipment, and for structural design inside the cryostat. Enjoys electronics projects and metalworking.
Qubits Inside Diamond
Nao: Let’s start with the term “diamond spin”. What exactly does “spin” mean in this context?
Kenichi: Spin is one of the quantum-mechanical properties of electrons and atomic nuclei. You can think of it as the orientation of an extremely small magnet. That orientation can be used as a qubit, the basic unit of information in a quantum computer.
In this research, we created atomic-scale defects in ultra-high-purity synthetic diamonds and used the electron spins trapped in those defects as qubits.
The synthetic diamond used in this research is much “cleaner” than natural diamond, with far fewer impurities. In a quantum computer, unwanted impurities can create noise, so it is important to introduce only the required defects with precision.
Nao: So, it is as if tiny magnets inside the diamond carry the quantum computer’s information.
Why Connect Qubits with Light?
"Nao: Optical connectivity is one of the key features of the diamond spin approach. What are the advantages of connecting qubits with light?
Kenichi: The greatest advantage is flexibility in how the qubits can be connected. Because light can transmit information with low loss, it allows qubits to be linked flexibly.
Our goal is a modular quantum computer that can be expanded by optically connecting modules, each containing a small number of qubits. This could enable configurations spanning multiple chips and multiple cryostats, which we believe will be important for future scaling.
Why Choose the Less-Explored SnV Center?
Nao: In research on diamond-based qubits, NV centers, defects in diamond associated with nitrogen atoms, are widely known. Why did Fujitsu choose the SnV center, which has a shorter research history?
Kenichi: NV centers have demonstrated excellent properties of diamond spin qubits. However, they present fundamental challenges for the highly efficient optical connectivity we are seeking.
Together with our research partner, Delft University of Technology, we selected the SnV center, whose optical emission properties are better suited to optical connectivity.
Rather than simply extending an established method, we worked backward from the future system we wanted to realize and selected the material accordingly. That was one of the major challenges of this research.
No Compromises, Down to a Single Screw Hole
Nao: What were some of the difficulties in realizing the diamond spin prototype, and were there any moments that made the work especially rewarding?
Masayuki: Our work covers everything from building the equipment needed to operate the diamond quantum computer to running quantum computations.
Quantum computers can be significantly affected by even the smallest error. We therefore went through extensive trial and error, from selecting equipment and wiring to positioning screw holes, designing structures with micrometer-level precision, and reassessing materials.
There is exhilarating satisfaction in work that lets us pursue every detail without compromise in a cutting-edge field.
The Moment of Success, Saved with a Trembling Cursor
Nao: When did you find this research most rewarding? Please share the moment from your perspectives.
Masayuki: One of the major challenges was delivering high-quality laser light to the diamond chip inside the cryostat and detecting the extremely faint light returning from it. We tried several methods without obtaining the results we wanted. In the end, a steady series of improvements enabled us to operate the prototype. There were many setbacks, but each one gave us valuable insights.
Itsuki: I was responsible for designing and building the optical systems required for quantum control and measurement. Bringing different technologies, including optical, high-frequency systems and the cryostat, together into one stable system required extensive adjustment and verification. It was deeply rewarding to see the prototype operate in the measurement environment we had carefully built ourselves, allowing the research to move to the next stage.
Ryota: I still remember the exact moment when we obtained the result we had been aiming for. When it appeared on the screen, my hand began to tremble without me realizing it. I remember selecting the save button with the cursor shaking. This achievement was the result of members with different areas of expertise, including device fabrication, equipment development, and software development, passing the baton from one to the next.
How Diamond Spin Could Open a Path to the Future of Quantum Computing
Nao: You have shared the potential of diamond spin from the perspective of researchers working toward practical quantum computing. What possibilities do you see for the approach in the future?
Kenichi: Practical quantum computers will require hardware capable of controlling many qubits with high precision. At Fujitsu, we are advancing diamond spin research in parallel with research and development on superconducting quantum computers. For the diamond spin approach, improving the performance of optical connectivity between qubits remains a key challenge. Looking ahead, these technologies may also enable connections between different types of quantum computers, including superconducting systems.
Diamond spin research is seeking to open a path toward more flexible ways of scaling quantum computers.
The research team’s journey has only just begun.
This prototype represents an important milestone toward scaling quantum computers using the diamond spin approach. Looking ahead, Fujitsu will continue developing technologies that connect diamond spin and superconducting systems, with the goal of realizing large-scale fault-tolerant quantum computers that leverage the strengths of each approach.
Stay tuned for further progress from the research team.
Related Information
“How Close Are We to Practical Quantum Computing?”
Quantum computing with Diamond spin
