The Wonderful Nature of Photons and Photonic Quantum Sensing

Quantum science and technology, which surpasses the limits of conventional technology by controlling the behavior of individual quantum particles such as electrons and photons, as well as the correlations between multiple quantum particles (quantum entanglement*1), is attracting attention. In particular, 2025 marks the 100th anniversary of the establishment of matrix mechanics by Heisenberg and others in 1925, which laid the foundation for modern quantum science. In recognition of this milestone, the United Nations General Assembly has declared 2025 as the UNESCO "International Year of Quantum Science and Technology."

Meanwhile, Kyoto University has long contributed to the development of quantum science through the work of many researchers, including Nobel Prize laureates Hideki Yukawa, Shin'ichirō Tomonaga, and Ken'ichi Fukui. Among them, Professor Shigeki Takeuchi's research group at the Graduate School of Engineering, Kyoto University, has been studying the behavior of light as a quantum for many years, achieving significant results in quantum entanglement and quantum interference, and promoting research on photonic quantum sensing, a new sensing technology utilizing the properties of quantum entanglement.

With the advancement of quantum entanglement and quantum science and technology utilizing it, the term "quantum entanglement" has become more widely recognized. However, to the best of our knowledge, there has been no exhibition of devices in Japan that actually operate on site to demonstrate the mysterious phenomena related to quantum entanglement, such as light in a quantum entangled state and the "violation of Bell's inequality," which was the subjet of the 2022 Nobel Prize in Physics. As a result, the general public has not had the opportunity to see or touch such phenomena directly.

This time, a team led by Professor Shigeki Takeuchi's laboratory members, in collaboration with the Kyoto University Office of Research Acceleration, the Kyoto University Office of Institutional Advancement and Communications, Kyoto University Museum, and Kyoto University Katsura Campus Administrative Office, among others, will present an exhibition that allows visitors to experience the mysterious world of "quantum entanglement" through devices that actually utilize entangled photon pairs. To the best of our knowledge, this is the first such exhibition open to the general public in Japan. Additionally, with the cooperation of Shimadzu Corporation and santec Holdings, the exhibition will introduce "photonic quantum sensing" technology using quantum-entangled light, which surpasses the limits of conventional technology, and its potential societal impact.

"Mitsuko"

For this exhibition, a character named "Mitsuko" was created, inspired by "Namino Mitsuko", who appears in Dr. Shinichiro Tomonaga's essay "The Trial of the Photon"^*2.
Mitsuko appears in various videos throughout the venue, helping to explain the astonishing phenomena of photons that visitors can experience through interactive installations.

ZONE1 | Prologue

Through Mitsuko’s video story, the narrative explains that light is made up of the smallest units called photons, describes the unique properties of photons, and illustrates the concept of entangled light.

ZONE2 | Experiment! The Mysterious World of Twin Photons

At the exhibition, visitors can try out three advanced experimental devices created by researchers at Kyoto University, and experience the mysterious behavior of entangled light.

Device 1　

The Birth of Twin Photons: Creating Entangled Light

Entangled light is generated in real time, and a live visualization of the entangled photons is displayed at the exhibition.

Device 2　

Indistinguishable Twin Photons: What Happens When They Meet and Interfere? An Experiment on Two-Photon Quantum Interference

In the world of quantum mechanics, interference between multiple physical processes can sometimes prevent events that would normally occur. Visitors can experience this phenomenon through an experiment in which a pair of photons is directed into a half mirror (beam splitter).

Device 3　

Even Far Apart, Still Entangled: Proving the Violation of Bell's Inequality

In quantum physics, the principle that physical phenomena are determined solely by the state of an object at its location—known as local realism—does not hold. At this exhibition, visitors can experience an experiment demonstrating the violation of Bell’s inequality, a phenomenon that was experimentally verified and recognized with the 2022 Nobel Prize in Physics. The setup uses entangled photon pairs to reveal this striking feature of the quantum world.

ZONE3 | Into the Future with Twin Photons

Through an interactive exhibit, visitors are introduced to photonic quantum sensing—a cutting-edge technology that uses entangled light to surpass the limits of conventional techniques. The display invites visitors to imagine how this innovation could transform our everyday lives in the future.

Quantum Optical Coherence Tomography (Q-OCT) (Equipment Provided by santec Holdings)

Visitors can experience observing the inside of their own finger using an OCT device. The exhibition then explains—through videos and data—how Q-OCT, which uses entangled light, can dramatically improve image resolution.

Quantum Infrared Spectrometer (Exhibition Coordinator : Shimadzu Corporation)

Visitors will have the opportunity to experience molecular identification using an infrared absorption spectroscopy device. Through explanatory videos and a mock-up illustrating its future design, the exhibition explains how quantum infrared spectroscopy using entangled photons can achieve significant miniaturization.

Epilogue — What's Next for Photonic Quantum Sensing

This exhibit provides an overview of the development of quantum mechanics and its connection with Kyoto University through a timeline starting from 1900. It also explains the technology of photonic quantum sensing using entangled photons and its potential impact on society. Additionally, the exhibit introduces the initiatives of the Photonic Quantum Sensing Social Implementation Consortium, recently established at Kyoto University.