Superconducting Quantum Electronics Research Team

Principal Investigator

PI Name Yasunobu Nakamura
Degree D.Eng.
Title Team Leader
Brief Resume
1992Researcher, Fundamental Research Laboratories, NEC Corporation
1997Senior Researcher, Fundamental Research Laboratories, NEC Corporation
2001Principal Researcher, Fundamental Research Laboratories, NEC Corporation
2001Visiting Scientist, Delft University of Technology, The Netherlands (-2002)
2002Frontier Researcher, Frontier Research Systems, RIKEN
2005Research Fellow, Fundamental and Environmental Research Laboratories, NEC Corporation
2008Visiting Researcher, Advanced Science Institute, RIKEN
2012Professor, Department of Applied Physics, The University of Tokyo
2012Professor, Research Center for Advanced Science and Technology, The University of Tokyo (-present)
2014Team Leader, Superconducting Quantum Electronics Research Team, RIKEN Center for Emergent Matter Science (-present)


We study quantum information electronics using artificial quantum systems based on superconducting circuits. Superconducting quantum bits are realized in Josephson-junction circuits and utilized as an elementary component for quantum information processing as well as a basic tool for quantum state control and measurement. Qubits are coupled with superconducting microwave resonators and transmission lines, enabling quantum state control of the microwave modes. Quantum optical technologies in the microwave domain will be developed and applied to quantum information science and technology such as quantum computing.

Research Fields

Physics, Engineering, Quantum Information Science


Quantum information
Quantum optics
Quantum bit


Microwave quantum optics in superconducting circuits

There is almost no energy dissipation in superconducting electrical circuits. Therefore, alternating current flows in a microwave resonator for a long period of time, and microwave signal travels along a transmission line without damping. Quantum mechanically, these can be described as storage and transmission of microwave ‘photons’ confined in the circuits. Similarly, superconducting quantum-bit (qubit) circuits consist of elements such as capacitors and inductors. However, due to strong nonlinearity induced by a Josephson junction, an additional inductive element, they can store at most a single quantum of microwave.

We combine those components, i.e., qubits, resonators, and transmission lines, for manipulation of quantum states of the microwave modes. Differently from the case in free space, electromagnetic field in the circuits is confined effectively either in zero-dimension (qubit and resonator) and one-dimension (transmission line), allowing efficient generation and detection of single photons and other nonclassical states of microwave. We have proposed and demonstrated a quantum node consisting of a driven superconducting qubit, which works as a microwave single-photon detector, for example.

Microwave single-photon detector using a superconducting qubit. (a) Schematic of the device, (b) Schematic of the circuit, (c) Energy-level diagram and the pulse sequence, (d) Detection quantum efficiency as a function of the qubit drive power and the signal frequency, (e) Quantum efficiency vs. qubit drive power.


Yasunobu Nakamura

Team Leader yasunobu.nakamura[at] R

Hiroki Ikegami

Senior Research Scientist

Kirill Shulga

Postdoctoral Researcher

Kun Zuo

Postdoctoral Researcher

Koichi Kusuyama

Technical Staff I

Koh-ichi Nittoh

Technical Staff I

Laszlo Szikszai

Technical Staff I

Yoshiro Urade

Visiting Researcher

Zhirong Lin

Visiting Scientist



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