電子のスピンやバレーを量子ビットの媒体として用いるための半導体材料の開発を行っています。半導体量子ビットは近接電子間の交換相互作用を用いるので、100nm程度の間隔で並べられ、集積化に優れています。本研究では、従来半導体量子ビットの研究で用いられてきたGaAsやSiに替わり、電子の量子コヒーレンスのさらなる向上や制御手法の 多様化が可能となる新たな材料の開拓を行っています。材料の作製から、微細加工プロセスの開発、特性評価までグループ内外の協力の元進めています。

We are developing semiconductor materials to place electron spins and valleys as media for quantum bits. In this research, we are searching for new materials that will enable further progress in quantum coherence of electrons and diversification of control methods, in place of GaAs and Si, which have been used in conventional semiconductor qubit research. We are collaborating both within and outside the group, from fabrication to microfabrication We investigate semiconductor materials for qubits utilizing electron spin or valley degree of freedom. We aim for new materials that enable further progress in quantum coherence and enhance the control and detecting schemes, compared with GaAs and Si, which have been used in conventional semiconductor qubit research. We are collaborating both within and outside the group, from material synthesis and microfabrication to low-temperature evaluation.process development and property evaluation.

• "Single-carrier transport in graphene/hBN superlattices"
  Nano Letters 20, 2551-2557 (2020)
• "Quantized conductance of one-dimensional strongly correlated electrons in an oxide heterostructure"
  Physical Review B 99, 121302(R)-1-6 (2019)

外部擾乱に強固な量子ビットとしてトポロジカル量子ビットの材料開発を行っています。トポロジカル量子ビットは超伝導ギャップ内に局在する準位を利用するので外乱に強い一方、制御と検出が難しく他の量子ビット技術よりも萌芽的段階にあります。本研究では、トポロジカル量子ビットを形成するのに適する半導体材料と超伝導材料の開発、およびその制御手法の開拓を進めています。

We study materials for topological qubits that are believed to be robust against external disturbances. Topological qubits utilize localized levels within the superconducting gap and are, therefore, resistant to external disturbances. However, they are difficult to control and detect, and are at a more emerging stage than other qubit technologies. In this research, we investigate semiconductor and superconducting materials, and their hybrid systems suitable for forming topological qubits.

• "Andreev reflection at the interface with an oxide in the quantum Hall regime"
  J. Phys. Soc. Jpn. 87, 124712-1-7 (2018)

超伝導や半導体を用いた固体量子ビットを動作させるには、多くの場合波形制御性の高いマイクロ波が用いられています。外部擾乱を抑制するため、量子ビット素子をマイクロ波のエネルギーより低い絶対零度近くの温度に下げる必要があります。その温度において効率的に動作する電子材料や磁性材料の開発を行っています。

Microwaves with highly controllable waveforms are often used to operate solid-state quantum bits using superconductors or semiconductors. To suppress external disturbances, the qubit device must be lowered to a temperature near absolute zero, below the microwave energy. We are developing electronic and magnetic materials that operate efficiently at these temperatures.