[Optical Control of Nuclear Spin Couplings]
　Interaction control between qubits is a fundamental requirement for quantum information processing. Nuclear spins in solids are attractive candidates for quantum memories because of their exceptionally long coherence times. However, their highly isolated nature has made it difficult to generate and control interactions only when needed. To address this challenge, we focused on photoexcited carriers generated in semiconductors and performed double-resonance NMR experiments under light illumination. These experiments revealed nuclear spin couplings that emerge exclusively under illumination and showed that both their strength and interaction range depend on the intensity of the excitation light. Furthermore, we demonstrated that these couplings are mediated by photoexcited carriers and that their magnitude can be controlled by adjusting the wavelength and intensity of the incident light. This technique represents an example of Hamiltonian engineering, in which interactions within a spin system are designed and manipulated using light. By optically bridging electron-spin and nuclear-spin systems, this approach provides a new route toward quantum control and offers new opportunities for semiconductor spintronics and quantum materials research.

[Development of Light-Illuminated NMR]
　As the technological foundation of this research, we developed a unique light-illuminated NMR system capable of highly sensitive measurements under optical excitation. Excitation light is delivered to samples inside a superconducting magnet through polarization-maintaining optical fibers, while a dedicated low-temperature probe enables measurements from cryogenic temperatures to room temperature. Together, these developments provide a stable environment for light-illuminated NMR experiments. The system enables highly sensitive detection of weak signals through optical-pumping-induced nuclear hyperpolarization, direct observation of spin interactions using double-resonance NMR techniques, selective observation of semiconductor heterointerfaces, and time-resolved studies of photoexcited states. More recently, the methodology has been extended to photoactive materials, where it serves as a powerful analytical tool for probing photoinduced phase transitions and other light-induced phenomena at the atomic level and in real time.

[References]
[1] A. Goto et al., Nature Communications 2, 378 (2011).
[2] A. Goto et al., npj Quantum Information 8, 59 (2022).
[3] A. Goto et al., Review of Scientific Instruments 77, 093904 (2006).
[4] A. Goto et al., Japanese Journal of Applied Physics 50, 126701 (2011).