[Developing quantum technologies based on the basic research to answers fundamental questions of quantum information science]

We try to develop quantum applications based on the understanding of the fundamentals of quantum information technologies. Our major research interests include quantum information processing based on the hybrid system consisting of photonic qubits and atom-like solid-state qubits and quantum secure communication. We focus on the spin-to-photon interface mediated by the color centers in solids and use it to connect quantum nodes consisting of integrated spin qubits to a photonic quantum network. Such a quantum network will be a building block for the long-distance quantum communication and networked quantum computing. For applications, we try to develop quantum secure communication technology including a quantum cryptography network system, long-distance quantum cryptography, quantum authentication and signature.

[Solid state quantum nodes]

Color centers in pure single crystalline solids with large bandgap, e.g. NV center in diamond, vacancy-related defects in silicon carbide, form a building-block for quantum nodes in which integrated electronic and nuclear spin qubits can be used as quantum registers. In order to build practical quantum nodes, we investigate spin-spin interaction which allows for connection among spin qubits in close proximity.

[Spin-photon quantum interface]

Controlling atom-photon interaction at the single quantum level is a crucial challenge in a wide range of perspectives for quantum information technologies. Especially, a coherent optical interface for long-lived spin qubits will be an essential building block for developing a large-scale quantum computing network and a quantum repeater for long-distance quantum communications. We aim to advance our vision of interconnecting defect spin qubits with high connectivity to realize a scalable quantum computing network.

[Fundamental research on quantum information science]

Although quantum communication and quantum computation aims practical applications, there are still lots of unknown aspects in quantum information science. In order to fully exploit the quantum advantages, therefore, it is essential to more deeply understand quantum world. In this sprit, we investigate fundamentals of quantum information such as the origin of quantum advantages, practical applications of quantum information processing, and resource efficient implementation of quantum information processing. The fundamental quantum phenomena are also experimentally investigated using solid and photonic qubits.

[Quantum secure communication]

Quantum secure communication is regarded as the closest commercial application among the quantum technologies. We are developing 1xN quantum key distribution system and verifying its feasibility in deployed fiber network. Also we are studying quantum authentication and signature for providing quantum solution about crypto service of integrity, authentication and non-repudiation. And we are preparing technologies for long-distance quantum cryptography including quantum repeater.