A research proposal by Prof. Shigeki Takeuchi (Graduate School of Engineering, Kyoto University), has been accepted as a research area "Super Quantum Entanglement" under the ERATO (*1) research program of the Japan Science and Technology Agency (JST) for FY2024, and the program started on October 1, 2024.

ERATO is characterized by the research director designs his/her ERATO project based on own unique concepts, brings together researchers with various expertise and backgrounds, organizes research groups of different scientific fields or functions, and supervises the project to develop new fields in science and technology.

Prof. Takeuchi has made many pioneering achievements in basic research on quantum information processing, such as the generation and detection of photons (*2), quantum entangled states (*3), and photonic quantum sensing (*4). In the research area of "Super Quantum Entanglement" (*5), theoretical research in computer science, mathematics, and physics will be combined with experimental research in quantum photonics to understand the fundamental principles of "Super Quantum Entanglement", including complex quantum states and quantum entangled light in previously unrealized wavelength ranges, and to study their applications. This research is expected to make scientific and societal contributions to a wide range of fields from materials science to medicine, with the goal of creating new quantum information processing beyond the current quantum computer (*6), improving the efficiency of quantum computer implementation methods, and creating new photonic quantum sensing.

1. Name of the ERATO research area

Super Quantum Entanglement

2. Outline of research area "Super Quantum Entanglement"

In recent years, the research and development of quantum technology using quantum superposition and entanglement, which are essential properties of quantum, has progressed rapidly. Quantum computers, in particular, are expected to solve problems that conventional computers cannot solve because they take too much time. However, there are a variety of challenges in achieving the 10 million qubit scale that is considered necessary for this purpose. In particular, as the number of parameters that specify a quantum state increases exponentially with respect to the number of qubits, the situation of entanglement in a quantum state becomes more complex, but how to efficiently identify it and how to efficiently write and read large amounts of information is not fully understood.

In this research area, theoretical research in information science, mathematics, and physics and experimental research in quantum photonics will be integrated, and research will be conducted to understand and utilize the basic principles of "Super Quantum Entanglement," which is a complex quantum state with many quanta, beyond the conventional concept of "quantum entanglement." This will challenge the development of new methods that enable the identification of complex quantum states and the efficient input and output of information. Specifically, we will conduct empirical research using photons, which are capable of state control at room temperature and long-distance transmission, among various quanta. In addition, we will conduct research on the realization and application of quantum entangled light in a wavelength range that has not been realized before.

This research area makes it possible to understand and utilize quantum states on a large scale, and is expected to create new quantum information processing beyond the current concept of quantum computers and to improve the efficiency of quantum computer implementation. We also aim to create new photonic quantum sensing using unexplored wavelength ranges. The accelerated development of these photonic quantum technologies is expected to have a significant academic and social impact on a wide range of fields from materials science to medicine.

3. Research promotion system for research area "Super Quantum Entanglement"

Prof. Shigeki Takeuchi (Kyoto University) serves as the research director, and Dr. Ryo Okamoto, Dr. Yu Mukai, and Dr. Satoshi Hara (The University of Electro-Communications) serve as group leaders. Three research groups consisting of researchers and graduate students from Kyoto University, The University of Electro-Communications, Kansai University, Kanazawa University, Osaka University, Hiroshima University, Tohoku University, and Kagawa University cooperate with research institutes in Japan and overseas.

Our research focuses on the integration of theoretical research in information science, mathematics, and physics with experimental research in quantum optics to understand and utilize the basic principles of "Super Quantum Entanglement" such as complex quantum states and entangled light in wavelength regions that have not been realized before.

4. Expected academic and social impact

Through this research, we aim to create new quantum information processing beyond the current concept of quantum computers, improve the efficiency of quantum computer implementation, and create new photonic quantum sensing using unexplored wavelength ranges. This is expected to contribute academically and socially to a wide range of fields, including finance, materials science, production technology, life science, and medicine. It also fosters human resources related to light quantum technology.

Notes

*1) ERATO

Exploratory Research for Advanced Technology (ERATO) is a research funding program of the Japan Science and Technology Agency (JST), which aims to lead science and technology-based innovations through novel, unique, and transformative basic research. In an ERATO project, the Research Director together with diverse team members devote themselves to challenging themes that drive forward new areas of science and technology. ERATO greatly values the leadership and originality of Research Directors and builds project systems with a focus on "people".

*2) Photon

A fundamental particle that makes up light and is the smallest unit of energy, proposed by Albert Einstein in 1905.

*3) Quantum Entanglement

A state in which multiple quanta are in a quantum mechanical superposition of specific correlations (combinations of states), such that the quanta cannot be regarded as having independent quantum states. In 1935, Einstein et al. pointed out the incompatibility of quantum entanglement with local realism, which was generally taken to be true, and subsequently verified the existence of quantum entanglement. The existence of quantum entangled states has been confirmed by experiments, and the Nobel Prize in Physics was awarded in 2022 for this pioneering work.

*4) Photonic Quantum Sensing

A new sensing technology that uses quantum entanglement and quantum mechanical superposition to overcome the sensitivity limit of conventional optical sensing or to realize new functions. Examples include "quantum entangled microscopy," which uses quantum entangled light as a light source to break through the sensitivity limit of laser light as a light source, and "quantum infrared spectroscopy," which enables spectroscopy in the infrared region using a photodetector in the visible region.

*5) Super Quantum Entanglement

Recently, Professor Takeuchi and his colleagues have shown that there are cases where it is useful to classify states in which many quanta form complex quantum correlations based on a concept different from the conventional concept of "quantum entanglement," such as whether they can be realized using only linear optical elements (Science Advances (2023)). In this research area, we refer to such states in which many quanta have complex quantum correlations and quantum entangled light in an unprecedented wavelength range as "Super Quantum Entanglement".

*6) Quantum Computer

A concept of a computer that uses "qubits" as its basic unit, which can be a superposition of 0s and 1s, whereas conventional computers use "bits" as their basic unit, which take the value of 0 or 1. It is expected to be able to solve problems in factoring and quantum simulation that are too time-consuming for conventional computers.

Researcher's Comments

Quantum science and technology have made rapid progress in recent years, and there seems to be a recent emphasis on "engineering" studies of their large-scale implementation and systemization. However, describing the complex quantum states that are now being realized requires an enormous number of parameters that are virtually impossible to estimate using conventional methods. Thus, it is not well understood how to efficiently estimate information from, and input/output to, complex quantum states. Entangled light has also been studied in a very limited range of wavelengths. In this ERATO research area, researchers from computer science, mathematics, theoretical physics, and experimental physics will work together to address these issues and create new scientific trends and new applications.