NTT Research’s Physics and Informatics (PHI) Lab and the Graduate School of Information Science (GSIS) at Tohoku University have jointly published a paper titled “Single photon coherent Ising machines for constrained optimization problems” in the Quantum Science and Technology journal. This publication is part of an ongoing collaboration focused on researching methods to develop a large-scale Coherent Ising Machine (CIM) simulation platform utilizing High-Performance Computing (HPC).
The newly proposed CIM employs an average photon number per pulse as small as one, which is significantly lower than that used in conventional CIMs. Its performance is evaluated through quantum theory. The research indicates that the single photon CIM can convert quantum entanglement into robust classical correlations between a measured pulse and other pulses through its quantum measurement and feedback process. Numerical simulations suggest that the performance of the single photon CIM is enhanced compared to conventional CIMs that leverage a higher number of photons per pulse.
The joint research, initiated in 2023, aims to enable cyber CIMs that can address combinatorial optimization problems, including those mapped to an Ising model. Tohoku University is researching methods to optimize third-generation cyber CIMs using HPC platforms, including examining vectorization and parallelization of kernels as accelerants. NTT Research’s PHI Lab contributes its focus on using nonlinear quantum optical technologies to build computing machines for real-world problems, drawing inspiration from fundamental principles of quantum physics.
This collaboration’s findings suggest a method for efficient machine learning accelerators and for solving complex computational problems. The ability of single photon CIM to convert quantum entanglement into robust classical correlations is central to its enhanced performance. NTT Research and Tohoku University plan to continue their collaboration toward the physical implementation of the single-photon CIM and the development of the Cyber CIM, a large-scale simulation environment, with the aim of supporting solutions to industrial problems.
Read the full announcement here and the paper in Quantum Science and Technology here.
July 13, 2025
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