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 system
Single electron manipulation
Nanodevices
Quantum coherence
Quantum correlations
Results
Observation 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 cloud. While the size of the Kondo cloud is one of the most important parameters that determine properties of manybody states containing multiple localized spins, its detection has remained elusive for the past 50 years.
We confined a localized spin in a semiconductor artificial atom coupled to conducting electrons, embedded it into an electronic interferometer, and observed real shape of the Kondo cloud. We found that its size is inverse proportional to the Kondo temperature and that the cloud mostly lies close to the localized spin accompanied with a long tail.
Our work is an important step towards understanding of manybody correlated states containing multiple magnetic impurities and development of novel quantum information devices based on the 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  

Yuya Shimazaki 
Research Scientist  
Han Ngoc Tu 
Postdoctoral Researcher  
David Pomaranski 
Postdoctoral Researcher  
Ryo Ito 
Postdoctoral Researcher  
Genki Okano 
Postdoctoral Researcher 
Publications
 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
 H. Edlbauer, S. Takada, G. Roussely, M. Yamamoto, S. Tarucha, A. Ludwig, A. D. Wieck, T. Meunier, and C. Bauerle
Nonuniversal transmission phase behaviour of a large quantum dot
 B. Bertrand, S. Hermelin, S. Takada, M. Yamamoto, S. Tarucha, A. Ludwig, A. D. Wieck, C. Bauerle, and T. Meunier
Fast spin information transfer between distant quantum dots using individual electrons
 F. Amet, C. T. Ke, I. V. Borzenets, J. Wang, K. Watanabe, T. Taniguchi, R. S. Deacon, M. Yamamoto, Y. Bomze, S. Tarucha, and G. Finkelstein
Supercurrent in the quantum Hall regime
 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
Email：
michihisa.yamamoto[at]riken.jp