"Quantum 2.0: Quantum Science and Technology Open Up New Horizons" aims at establishing a solid foundation for quantum science and technology, which have a potential to develop Japan's economy, industry, and national security by controlling the microscopic behavior of atoms, electrons, photons, etc., as described by quantum mechanics. "Quantum 2.0" is about the ability to control and utilize quantum-specific properties which were difficult to use in the past, such as quantum coherence and entanglement. The related wide-ranging R&D should be promoted along with efforts to address social and economic issues, to strengthen national security and industrial competitiveness, and to form new academic fields, communities and researcher networks.

With the growth of the Internet of Things (IoT), more and more people, devices, and organizations are connected to the network, and a large amount of digital data called "big data" is being generated, collected, and stored. In a knowledge-intensive society led by the advent of a digitized society, the interdependence between countries becomes deeper and more complex, and at the same time, various constraints on Japan's economy and the maintenance or improvement of the living standard of the people are also becoming prominent. Quantum science and technology is one of the new technological fields that show signs of rapid development in view of solutions to social issues and industrial applications.

The movement to apply quantum mechanics to computation and communication goes back to Feynman's conceptual proposal of quantum simulation in the 1980s. However, it was not until the late 1990s, when the quantum's behavior was able to be manipulated and controlled as theoretically expected, that there was significant R&D progress after the birth of quantum information science from the merger of quantum mechanics and information science. Recently, in parallel with experimental verification of important properties such as quantum coherence and entanglement, various physical systems are known as a qubit which serves as a medium of quantum information; their coherence time, during which the qubit can maintain quantum information, has so far been extended by orders of magnitude. Thus, quantum science and technology have promised the possibility of creating new values in terms of addressing social issues and industrial applications through the advancement of high manipulation and control technology.

Therefore, in major countries, very large-scale government investments have been made based on the common understanding that quantum science and technology can provide national security and economic benefits. In contrast, in Japan, while some of the related cutting-edge R&D activities are being internationally recognized, they are not integrated among universities, national labs, companies, etc., which would be a major barrier to establishing our nation's leading position in many fields that will create a new trend in the world. The R&D of quantum science and technology should be strategically promoted through enhancement of international competitiveness, resolution of social and economic issues, and creation of new academic fields, thereby leading to the future growth and development of Japan.

In the following, we will show the future R&D subjects in the four major areas of quantum science and technology and in the area of a common quantum technological platform for deepening and developing these areas.

(i) Quantum computing and simulation: The R&D of hybrid quantum-classical algorithms indispensable for killer applications of NISQ (Noisy Intermediate-Scale Quantum computing) machines such as quantum-chemical calculations and quantum machine learning, development of real machines with superconducting qubits as the building blocks, enhancement of the overall computer architecture toward the realization of the fault-tolerant quantum computer as a final goal, and basic R&D related to the control of various qubit systems should be promoted. For the R&D of quantum simulators, it is necessary to establish modeling and simulation techniques for complex quantum many-body systems that intrinsically require large amounts of quantum entanglement and coherence.

(ii) Quantum measurement and sensing: The R&D should be promoted with a strong focus on social implementation by clarifying the specific application fields or industrial exits. In sensing technology using diamond nitrogen-vacancy (NV) centers, quantum entanglement of light or matter, and room-temperature nuclear hyperpolarization, it is important to develop applications for biomedical measurement and to produce or commercialize prototypes for medical and diagnostic purposes. Atomic interferometer-type gyroscopes and optical lattice clocks should be miniaturized and stabilized to demonstrate a proof-of-principle and practical application of self-location estimation and relativistic geodesy, respectively. Particularly, Japan's original optical lattice clocks are expected to contribute to the redefinition of the SI second by international organizations.

(iii) Quantum cryptography and communications: Importantly, in the short term, we should search for killer applications of quantum key distribution (QKD) devices, identify their application fields by early commercialization or trial use, and lower their price. In the medium-to-long term, it is necessary to promote the R&D of the satellite-based QKD, long-range QKD, and new-principle-based QKD technologies. Furthermore, for the development of high-speed and long-distance communications, the R&D of all-photonic quantum repeaters as well as quantum memories is required, thereby demonstrating a proof-of-principle of scalable quantum repeaters to realize a small-scale quantum network. Intensive standardization activities in international organizations are also required for the future.

(iv) Quantum materials: We should continuously create new quantum materials that are robust to environmental disturbances and produce attractive functions contributing to the next generation of quantum science and technology; new concepts, materials and technologies that induce innovation in existing fields are also required. Representative examples are topological quantum materials, spintronic materials, energy-conversion materials, and photonic materials.

(v) Common quantum technology platform: It is necessary to develop quantum measurement, manipulation, and control technologies such as the technologies of single-photon control, qubit systems, and coupling or interface between qubits, etc., and their theoretical basis. Microfabrication and analysis techniques and cryogenic electronics should be advanced as essential technologies.

Due to their very different timelines, these R&D subjects should be undertaken in both the short-to-medium (up to 10 years) and medium-to-long (up to 20 years or more) terms. Another important measure to promote R&D is the formation of core hubs, which could become internationally recognized and therefore be expected to serve as a place to attract excellent researchers from Japan and overseas.

To address social and economic issues, R&D should be targeted regarding the following five strategic subjects: "quantum computer", "quantum measurement and standard", "quantum medicine and diagnosis", "quantum security", and "topological materials." For this purpose, three approaches are important; i.e., "enhanced fusions of scientific disciplines and technological areas", "promotion of open innovation", and "encouragement of start-ups and improvement of investment environments". In addition, we need to pursue international cooperation while ensuring our superiority considering Japan's R&D strengths and weaknesses. National security and industrial competitiveness should also be strengthened through standardization and intellectual property management.

In order to create new academic fields, communities, and researcher networks for supporting the R&D in the long term, we need policy support that sustainably enables fusions and diversification of scientific disciplines and technological areas, human-resource development, and brain circulation in Japan and overseas. Importantly, these efforts should enhance the interactions with the activities of the above strategic R&D subjects towards resolving social and economic issues, thereby maximizing their synergistic effects.