Kawasaki, Japan, March 24, 2025 -- Fujitsu Limited today announced the world’s first demonstration of a complete universal quantum gate set for diamond spin qubits with an error probability below 0.1%, achieving a fidelity among the highest reported over all quantum hardware technologies. This collaboration with QuTech, a leading quantum technology research institute of Delft University of Technology (TU Delft), marks an important step for the diamond spin method towards carrying out quantum error correction and realizing practical quantum computing. The findings were published in Physical Review Applied on March 21, 2025.

The newly developed technology utilizes high-purity diamonds to create a stable two-qubit system comprising an electron spin and nitrogen nuclear spin within a nitrogen-vacancy (NV) center, a kind of atomic defect that can be harnessed for quantum computing. The team used advanced techniques to eliminate the impact of environmental noise on qubits and measure the performance of the quantum gates, achieving over 99.9% fidelity for both single- and two-qubit gates across a universal gate set. This surpasses the threshold required for quantum error correction.

Going forward, Fujitsu and QuTech will continue to collaborate, increasing the number of qubits used and developing optical quantum chips and control circuits to advance research toward the early practical application of diamond spin quantum computers.

Overcoming challenges in quantum computing with diamond spin qubits

Diamond spin technology utilizes the spins (electron and nuclear spins) formed by color centers—specific defects—within diamond crystals as qubits. Diamond spins can hold quantum states for relatively long periods of time, which makes them promising as high-performance qubits. Furthermore, their operational temperature is approximately 100x higher than that of superconducting qubits, making them easier to work with. The capability of diamond spin qubits to transmit quantum states using photons (fundamental particles of light) also allows for optical interconnects, providing a promising path towards scalable quantum computers and distributed computing via quantum networks.

Overview of the technology

1. Reduced environmental noise using high-purity diamonds

Qubits were created using NV centers in diamonds jointly developed by Element Six and TU Delft. This was possible because of the diamonds low carbon-13 isotope concentration (0.01% reduced from 1%.) This removed environmental noise, creating a stable two-qubit system with one formed by the electron spin of the defect center, the other by its nuclear spin.

2. Decoupling gates designed to mitigate environmental noise

Decoupling gates are sequences of controlled pulses designed to remove the impact of environmental noise on the qubits and extend their ability to retain quantum information.

3. Application of gate set tomography

The team applied gate set tomography, a high-precision technique to measure the performance of qubits and quantum gates, to diamond spin qubits to optimize quantum gate operations. This provided complete information on gate errors, enabling optimization of all parameters of quantum gate operations, including gate pulse strength.

Future Plans

Moving forward, Fujitsu and QuTech will focus on applying the newly developed technology to systems with a larger number of nuclear spins and developing technologies for high-precision optical interconnects between distant electron spin qubits to increase the number of manageable qubits. Furthermore, the team will accelerate research and development towards realizing a scalable quantum computing system, including integration technologies with control circuits using cryo-CMOS low temperature semiconductor integrated circuits.

Professor Tim Taminiau, Delft University of Technology comments:

While there is a long and challenging road ahead, the fact that we demonstrated gate fidelities above 99.9% fulfills one of the key requirements for scalable quantum computation.

Shintaro Sato, Fellow SVP & Head of Quantum Laboratory at Fujitsu Research, Fujitsu Limited, comments:

This result showcases the significant potential of diamond spin technology for realizing a practical quantum computer. Fujitsu now aims to develop a prototype diamond spin quantum computer as it continues to work toward the realization of practical quantum computing.