Quantum Functional System Research Group

Principal Investigator

PI Name Seigo Tarucha
Degree D.Eng.
Title Group Director
Brief Resume
1978Staff Member at the Basic Research Laboratories of Nippon Tel. & Tel. Corp.
1985Senior Researcher at the Basic Research Laboratories of Nippon Tel. & Tel. Corp.
1986Visiting Scientist, Max-Planck-Institute FKF (Stuttgart, Germany)(-1987)
1989Principal Researcher at the Basic Research Laboratories of Nippon Tel. & Tel. Corp.
1990Group Leader, Research Group on Electron Transport in Low-Dimensional Semiconductor Structures, NTT Basic Research Laboratories(-1998)
1994Distinguished Scientist, NTT Basic Research Laboratories (-1998)
1995Visiting Professor, Technical University of Delft (The Netherlands)
1998Professor, Department of Physics, University of Tokyo (-2004)
2004Professor, Department of Applied Physics, University of Tokyo (-2018)
2012Visiting Professor, Institut Néel CNRS, université Joseph Fourier (France)
2013Division Director, Quantum Information Electronics Division, RIKEN Center for Emergent Matter Science (-present)
2013Group Director, Quantum Functional System Research Group, RIKEN Center for Emergent Matter Science (-present)
2018Deputy Director, RIKEN Center for Emergent Matter Science (-present)
2019Guest Professor, Department of Physics, Tokyo University of Science (-present)
2020Team Leader, Semiconductor Quantum Information Device Research Team, RIKEN Center for Emergent Matter Science (-present)



We study hardware and underlying physics for quantum information processing with quantum control of solid-state quantum states. Quantum information processing is an ideal information technology whose operation accompanies low-energy dissipation and high information security. The purpose of our group is to demonstrate the ability of the solid-state information processing based on concepts of quantum coherence and entanglement in semiconductor, topological phases, and photons to spin conversion, and finally outline a path for the realization. The specific research targets are "quantum computing" constructed by gate-based quantum logic operations, "quantum interface" useful for quantum repeaters, "quantum devices" relevant for the quantum control, and “topological control” providing new concepts of quantum information. We investigate best suited quantum circuits and devices, and fundamental physics of quantum entanglement, quantum dynamics, and topological particles.

Research Fields

Physics, Engineering


Quantum computing
Quantum simulation
Photon-spin interface
Spin control
Quantum dots
Topological particles


An ultra-high fidelity quantum dot qubit in a silicon quantum dot

The building block of quantum computers, or the smallest unit of quantum information, is called a qubit. A very large number of high-quality qubits will be needed to build a quantum computer. Single electron spins in quantum dots are a strong candidate as qubits, as they likely benefit from modern electronics integration technology, once sufficient quality is reached.

Enhancing the qubit quality means improving both coherence time and control time, challenging the trade-off commonly observed between these. In this work, we fabricated a quantum dot on an isotopically-clean silicon wafer to increase the coherence time, and deposited a micromagnet nearby to decrease the control time by its slanting magnetic field. With the coherence time ten times longer and the control time two orders of magnitude shorter than conventional within a single device, we implement highly coherent qubit operations (Fig. B). We further demonstrate >99.9% control fidelity (precision), above the fault-tolerance threshold.

Our work offers a promising route to large-scale, ultra-high-fidelity spin-qubit systems in silicon.


(Fig. A) Schematic view of the quantum-dot qubit device
(Fig. B) Chevron resulting from ultra-high fidelity spin rotations


Seigo Tarucha

Group Director tarucha[at]riken.jp R

Takashi Nakajima

Research Scientist

Kenta Takeda

Research Scientist

Takashi Kobayashi

Research Scientist

Chien-Yuan Chang

Postdoctoral Researcher

Akito Noiri

Special Postdoctoral Researcher

Sadashige Matsuo

Special Postdoctoral Researcher

Juan Sebastian Rojas Arias

Research Associate

Yosuke Sato

Research Associate

Xin Liu

Technical Staff I

Hima Annapoorna Kavuri

Technical Staff I

Yago Baltasar Del Valle Inclan Redondo

Visiting Researcher

Tomohiro Otsuka

Visiting Scientist

Michael Desmond Fraser

Visiting Scientist

Raisei Mizokuchi

Visiting Scientist

Yohei Kojima

Student Trainee

Takamoto Yokosawa

Student Trainee

Yuusuke Takeshige

Student Trainee

Miuko Tanaka

Student Trainee

Kento Ueda

Student Trainee

Yoshihiro Uehara

Student Trainee

Masahiro Tadokoro

Student Trainee



2-1 Hirosawa, Wako, Saitama 351-0198 Japan