Progress Report
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Large-scale and high-coherence fault-tolerant quantum computer with dynamical atom arrays[1] Large-scale and high-coherence fault-tolerant quantum computer with dynamical atom arrays
Progress until FY2025
1. Outline of the project
In this R&D theme, we aim to construct a practical cold-atom, fault-tolerant quantum computer with a large array of cold-atom qubits assembled by the “optical tweezers” technique, in which atoms are individually captured by laser beams. Our approach includes a dynamic qubit array that allows each atomic qubit to be moved before and/or during the computation for algorithm-dependent optimization of the initial configuration of the qubits, gate manipulation, and error detection and correction. Furthermore, through close collaborations between leading academia and industries, we will integrate and package all the components including vacuum chambers, laser sources, optics, electronics, and imaging devices to achieve unprecedented stability and usability. These advancements will enable precise and reliable control of large atomic-qubit arrays and realize fault-tolerant quantum computers that will revolutionize the economy, industry, and national security by 2050.
To realize this goal, we are conducting R&D on the following items: a scalable cold-atom quantum computer platform with a vacuum chamber preserving a large array of atomic qubits; high-coherence and high-fidelity quantum gates; quantum error detection and correction architecture optimized for cold atoms (both theory and experiment); and laser systems dedicated to cold-atom quantum computers underlying the above three R&D items. From the viewpoint of diversity, we are conducting R&D with rubidium (Rb), ytterbium (Yb), and strontium (Sr) atomic qubits.
2. Outcome so far
In the development of the quantum computer platform, we have successfully completed a Rb full-stack quantum computer (Fig.1), as well as a control system dedicated to large-scale cold-atom quantum computing.
In the development of the quantum gates, we have successfully developed underlying technologies with Rb atoms for high-fidelity quantum gate operations including atomic wavefunction squeezing, ultra-precise optical tweezers, super-resolution optical imaging, and suppression of the intensity fluctuations of laser pulses driving our ultrafast gates. We also successfully demonstrated the coherent excitation to Rydberg states applicable to two-qubit gate operations and the coherent control of clock-transition qubits with Yb atoms (Fig.2).
In the development of the quantum error detection and correction architecture, we have successfully demonstrated nondestructive measurements of Rb-atom qubits with 94% fidelity allowing for the post-measurement re-use of those atomic qubits. We also successfully determined the magic wavelength for a newly identified ultra-narrow linewidth optical transition applicable to nondestructive measurements of Yb-atom qubits and successfully resolved this transition with a spectral width of several tens of Hz.
In the development of the high-stability and high-intensity laser systems, we developed a compact and high-power atom-trapping laser based on a Distributed Face Cooling (DFC) structure. We also successfully fabricated the prototype of bonded chips of Cr:LiSAF and sapphire crystals (Fig. 3). The generation of highly stable pulses from a new laser amplifier system with the DFC chip was also demonstrated.
3. Future plans
In the second stage of the Ohmori Moonshot Project that started in April 2026, we will operate the full-stack quantum computer to further develop and improve the integration and control technologies, upgrade the system toward fault tolerance and larger scales, and enable high stability and high-fidelity quantum computation for extended periods of time. Our goal is to realize a large-scale, high-performance, cold-atom fault-tolerant quantum computer with quantum error detection and correction capabilities available to external users. We will also develop highly stable and high-intensity laser systems necessary for the goal, as well as various innovative technologies that will enable further breakthroughs.