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.
1986Visiting Scientist , MPI (Stuttgart, Germany)(-1987)
1990Leader, Research Program on Electron Transport in Low-Dimensional Semiconductor Structures, NTT Basic Research Laboratories(-1998)
1993Distinguished member of technical staff, NTT Basic Research Laboratories (-1998)
1995Distinguished member of technical staff, NTT Basic Research Laboratories (-1998)
1998Professor, Department of Physics, University of Tokyo
2004Professor, Department of Applied Physics, University of Tokyo (-present)
2012Visiting Professor, Institut Néel CNRS, université Joseph Fourier(France)
2013Group Director, Quantum Functional System Research Group, Quantum Information Electronics Division, RIKEN Center for Emergent Matter Science (-present)
2018Deputy Director, 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 using quantum operations of quantum coherence and entanglement in semiconductor and superconductor nanostructures and finally outline a path for the realization. The specific research targets are "quantum computing" including quantum logic operation and quantum simulation, "quantum interface" which can offer quantum memory and relay, and "quantum nanodevices" relevant for the quantum control. We investigate architectures for best suited quantum systems, science and technology for both materials and devices, and fundamental physics of quantum entanglement, decoherence and spin correlation.

Research Fields

Physics, Engineering


Quantum computing
Quantum simulation
Quantum relay
Spin control
Quantum dots


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

Jun Yoneda

Research Scientist

Hiroshi Kamata

Research Scientist

Kenta Takeda

Postdoctoral Researcher

Akito Noiri

Postdoctoral Researcher

Sen Li

Postdoctoral Researcher

Tomohiro Otsuka

Visiting Scientist

Michael Desmond Fraser

Visiting Scientist

Marian Nicola Joachim Marx

Visiting Technician

Takumi Ito

Student Trainee

Juan Sebastian Rojas Arias

Student Trainee

Yohei Kojima

Student Trainee

Yosuke Sato

Student Trainee

Takamoto Yokosawa

Student Trainee

Yuusuke Takeshige

Student Trainee

Miuko Tanaka

Student Trainee

Kento Ueda

Student Trainee

Shotaro Kano

Student Trainee



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