The Graduate School of Information Science (GSIS) at Tohoku University, together with Physics and Informatics (PHI) Lab at NTT 雷速体育_中国足彩网￥在线直播, Inc., have jointly published a paper in the journal Quantum Science and Technology. The study involved studying a combinatorial clustering problem, a representative task in unsupervised machine learning.
Joint 雷速体育_中国足彩网￥在线直播 Agreement on Large-scale Cyber CIM with High-Performance Computing
Together, the two institutions are researching methods to bring to life a large-scale CIM simulation platform using conventional high-performance computing (HPC). This large-scale CIM will be critical to enabling cyber CIMs that will be widely accessible for solving hard NP, NP-complete and NP-hard problems.
The collaboration kicked off in 2023 with Hiroaki Kobayashi, Professor at the GSIS at Tohoku University, acting as the principal investigator for the joint research agreement (JRA), with PHI Lab Director Yoshihisa Yamamoto joining as the NTT 雷速体育_中国足彩网￥在线直播 counterpart to Kobayashi. As part of the JRA, Tohoku University will research methods to optimize the third-generation cyber CIM using HPC platforms. Following this research, Tohoku University will examine vectorization and parallelization of kernels as accelerants and consider optimization of data management in the cache memory hierarchy, as well as ways to scale cyber CIM to 100 million spins with sparse connection on an appropriate platform.
"NTT 雷速体育_中国足彩网￥在线直播's collaboration with GSIS at Tohoku University will unlock energy efficient and optimized machine learning accelerators," said Yoshihisa Yamamoto, PHI Lab Director at NTT 雷速体育_中国足彩网￥在线直播. "By combining quantum optical formalism and digital electronic platform, our work with Tohoku University brings us one step closer to bringing to life a large-scale CIM simulator, enabling cyber CIM simulators that offer users an accessible and efficient way to solve stochastic differential equations that describe a DOPO network with quantum measurement and feedback circuit."
Critical to the JRA is the PHI Lab's mission to use nonlinear quantum optical technologies to build simple, efficient and practical computing machines for real-world problems by redesigning analog/digital hybrid computers using the fundamental principles of quantum physics and neuroscience, drawing inspiration from biological computers present in brains. As part of this mission, the PHI Lab relies on the CIM, which is a network of degenerate optical parametric oscillators (DOPOs) programmed to solve combinatorial optimization problems mapped to an Ising model. The Ising model is a mathematical abstraction of magnetic systems composed of competitively interacting spins, or angular momenta of fundamental particles.
A Striking Result
In contrast to the conventional and experimental coherent Ising machines (CIM) reported previously in Science 354, 603 (2016) and Science 354, 614 (2016), a newly proposed CIM employs an average photon number per pulse as small as one, which is eight orders of magnitude smaller than the photon number existing in the conventional CIMs. In such an extremely weak light limit, performance of CIMs must be evaluated through quantum theory rather than classical heuristic models.
The result of a numerical simulation based on the quantum model was unexpected, which is in sharp contrast to a standard picture. Initially, it was hypothesized that a CIM with a single photon per pulse suffers from poor signal-to-noise ratio in the measurement of internal pulse amplitudes and challenges to storing the analog amplitude information stably. Under this assumption, the performance is expected to be much worse than the conventional CIM with 10^8 photons per pulse.
However, the research team found that within a numerical simulation, the result is the complete opposite. Figure 1 (below) shows the probabilities of success for finding exact solutions for various instances by the single photon CIM and the conventional CIM with 10^8 photons per pulse. The figure indicates the performance of the single photon CIM is much better than that of a conventional CIM.
Quantum Enhancement Mechanism
The superior performance of the single photon CIM discovered by the collaboration originates from a quantum mechanical effect. At a measurement port of the CIM, an extraction beam splitter generates a correlated internal pulse and extracted pulse to be measured, that is, the amplitude of the extracted pulse carries information of the internal pulse amplitude. This correlation between the internal and extracted pulses penetrates a quantum regime in spite of background noise, which indicates that there is quantum entanglement between these two pulses in the single photon CIM.
Despite the fragile nature of quantum entanglement that can be easily destroyed by optical loss and background noise, the single photon CIM was able to convert the fragile quantum entanglement into robust classical correlations between a measured pulse and all the other pulses through its quantum measurement and feedback process. The generation of quantum entanglement and its immediate conversion to classical correlation is key for understanding the improved performance of the single photon CIM, which is absent in conventional CIMs that leverage many photons per pulse.
Looking ahead, NTT 雷速体育_中国足彩网￥在线直播 will continue to collaborate with GSIS at Tohoku University to move toward the physical implementation of the single-photon CIM, building on its theoretical validation and developing Cyber CIM, a large-scale simulation environment. This effort will pave the way for fast and energy-efficient solutions to real-world industrial problems.
- Publication Details:
Title: Single photon coherent Ising machines for constrained optimization problems
Authors: Masahito Kumagai, Yoshitaka Inui, Edwin Ng, Satoshi Kako, Kazuhiko Komatsu, Hiroaki Kobayashi and Yoshihisa Yamamoto
Journal: Crystal Growth & Design
DOI: 10.1088/2058-9565/addde5
雷速体育_中国足彩网￥在线直播:
Hiroaki Kobayashi
Email: koba
tohoku.ac.jp
