Quantum Electron Device Research Unit

Principal Investigator

PI Name Michihisa Yamamoto
Degree D.Sci.
Title Unit Leader
Brief Resume
2004Ph. D. in Physics, The University of Tokyo, Japan
2004Research Associate, Department of Applied Physics, The University of Tokyo
2014Lecturer, Department of Applied Physics, The University of Tokyo
2017Associate Professor, Quantum-Phase Electronics Center, School of Engineering, The University of Tokyo (-present)
2017Unit Leader, Quantum Electron Device Research Unit, RIKEN Center for Emergent Matter Science (-present)


We develop quantum electron devices based on manipulation and transfer of quantum degrees of freedom in solids. We employ quantum electron optics, where quantum states of propagating electrons are manipulated in a single electron unit, and experiments on transfer and manipulation of novel quantum degrees of freedom in atomic-layer materials. These experiments aim to reveal physics of quantum coherence, quantum correlations, and quantum conversions, as guiding principles for quantum electron devices. We also employ state of the art quantum technologies to solve long-standing problems in condensed matter physics from microscopic points of view.

Research Fields

Physics, Engineering


Two-dimensional electron system
Single electron manipulation
Quantum coherence
Quantum correlations


Scattering phase of an electron wave through an artificial atom revealed by quantum electron optics experiment

The phase of an electron wave function, a counterpart of the wave function amplitude characterizing the electron probability density, plays an important role in quantum devices. Techniques for precise measurement and control of the phase shift of an electron wave are useful not only for development of quantum devices but also for investigation of microscopic quantum effects in solids that cannot be detected in conventional transport experiments. We employ quantum electron optics, where the quantum state of a propagating electron is manipulated, to investigate scattering of an electron wave by an artificial atom.

In scattering problems, the scattering phase contains essential physical information as well as the scattering amplitude characterizing the conductivity. We embed a quantum dot into an original electronic interferometer allowing us to measure precisely the scattering phase through an artificial atom. In addition to the Friedel sum rule, which connects the number of electrons in the quantum dot to the scattering phase, we have revealed influences of the parity of orbital wave function and the interaction between a local spin confined in the quantum dot and conducting electrons in the reservoirs, i.e. the Kondo effect. The observed π/2 phase shift in the Kondo regime is the hallmark of Kondo effect interpreted as the fingerprint of local moment screening.

(a) Scanning electron micrograph of the device and measurement setup. Output currents I1 and I2 oscillate with opposite phase as a function of the difference of phase shift acquired in the two paths of the Aharonov-Bohm ring. (b) Phase shift through a quantum dot extracted from the oscillating component of the measured current I = I1 I2, plotted with the oscillation amplitude and the total conductance. Phase lapse appears between Coulomb peaks (maximum of the conductance through the quantum dot), depending on the parity of orbital wave function in the quantum dot.
Figure (b) taken from Nature Communications 8, 1710 (2017).


Michihisa Yamamoto

Unit Leader