Quantum Electron Device Research Team
Principal Investigator
PI Name  Michihisa Yamamoto  

Degree  D.Sci.  
Title  Team Leader  
Brief Resume 


Outline
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 atomiclayer 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 longstanding problems in condensed matter physics from microscopic points of view.
Research Fields
Physics, Engineering
Keywords
Twodimensional electron systems
Single electron manipulation
Nanodevices
Quantum coherence
Quantum correlations
Results
Electrical control and quantum simulation of the Kondo screening cloud
The Kondo effect, an archetype of manybody correlations, arises from the interaction between a localized spin and surrounding conducting electrons. Since conducting electrons form a spin cloud to screen the localized spin, the Kondo state is also called as the Kondo screening cloud. The size of the Kondo cloud is inverse proportional to the Kondo temperature and the cloud has the universal shape.
The Kondo cloud is formed by confining a localized spin in a semiconductor artificial atom coupled to conducting electrons. Our recent experiment has revealed that the quantum interference can deform the cloud and modulate the entanglement between the localized spin and conducting electron spins. We are now investigating systems, where multiple Kondo clouds overlap with one another. Such strongly correlated systems are quantum manybody states, where quantitative calculation of physical quantities is difficult. Precise control of quantum systems based on the tunable Kondo cloud is expected to enable quantum simulations of systems with longrange spin coupling.
Quantum control of electron waves and measurement of the scattering phase
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.
We recently apply this technology for quantum control of electron waves to the quantum information processing. Based on the electron wave states, we attempt to control delocalized quantum bits defined by ondemand special quasiparticles. Similarly to the photon qubit, where the number of qubits is not limited by the hardware size, this may open up a way to control numerous semiconductor qubits in a compact hardware. Our aim is to bring a paradigm shift in semiconductor quantum architectures, from vast infrastructure to a much smaller hardware, by realizing quantum control of ondemand qubits.
Members
Michihisa Yamamoto 
Team Leader  michihisa.yamamoto[at]riken.jp  

Yuya Shimazaki 
Research Scientist  yuya.shimazaki[at]riken.jp  
Han Ngoc Tu 
Postdoctoral Researcher  
David Pomaranski 
Visiting Scientist 
Publications
 M. Tanaka, K. Watanabe, T. Taniguchi, K. Nomura, S. Tarucha, and M. Yamamoto
Temperatureinduced phase transitions in the correlated quantum Hall state of bilayer graphene
 R. Ito, S. Takada, A. Ludwig, A. D. Wieck, S. Tarucha, and M. Yamamoto
Coherent beam splitting of flying electrons driven by a surface acoustic wave
 M. Tanaka, Y. Shimazaki, I. V. Borzenets, K. Watanabe, T. Taniguchi, S. Tarucha, and M. Yamamoto
Charge Neutral Current Generation in a Spontaneous Quantum Hall Antiferromagnet
 I. Borzenets, J. Shim, J. C. H. Chen, A. Ludwig, A. D. Wieck, S. Tarucha, H. S. Sim, and M. Yamamoto
Observation of the Kondo screening cloud
 Y. Shimazaki, M. Yamamoto, I. V. Borzenets, K. Watanabe, T. Taniguchi, and S. Tarucha
Generation and detection of pure valley current by electrically induced Berry curvature in bilayer graphene
21 Hirosawa, Wako, Saitama 3510198 Japan
Email：
michihisa.yamamoto[at]riken.jp