Klaus Ensslin

Electrostatically defined quantum dots in bilayer graphene offer a promising platform for spin qubits with presumably long coherence times due to low spin-orbit coupling and low nuclear spin density. We employ a capacitively coupled charge sensor to study the time dynamics of the excited state using the Elzerman technique. We find that the relaxation time of the excited state is of the order of milliseconds. We perform single-shot readout of our two-level system which is an important step for developing a quantum information processor in graphene. We also present quantum devices fabricated on magic-angle-twisted bilayer graphene and demonstrate operation of a Josephson junction and a SQUID.

This work was done in collaboration with Lisa Maria Gächter, Rebekka Garreis, Chuyao Tong, Max Josef Ruckriegel, Folkert Kornelis de Vries, Annika Kurzmann, Wister Wei Huang, Elias Portoles, Giulia Zheng, Peter Rickhaus, Shuichi Iwakiri, Takashi Taniguchi, Kenji Watanabe, and Thomas Ihn.

1.     Chuyao Tong, Rebekka Garreis, Angelika Knothe, Marius Eich, Agnese Sacchi, Kenji Watanabe, Takashi Taniguchi, Vladimir Fal'ko, Thomas Ihn, Klaus Ensslin, and Annika Kurzmann, “Tunable valley splitting and bipolar operation in graphene quantum dots”, Nano Lett. 21, 1068 (2021)

2.     Rebekka Garreis, Angelika Knothe, Chuyao Tong, Marius Eich, Carolin Gold, Kenji Watanabe, Takashi Taniguchi, Vladimir Fal'ko, Thomas Ihn, Klaus Ensslin, Annika Kurzmann, “Shell Filling and Trigonal Warping in Graphene Quantum Dots”, Phys. Rev. Lett. 126, 147703 (2021)

3.     F. K. de Vries, E. Portoles, G. Zheng, T. Taniguchi, K. Watanabe, T. Ihn, K. Ensslin, and P. Rickhaus, “Gate-Defined Josephson Junctions in Magic-Angle Twisted Bilayer Graphene“, Nature Nano 16,  760 (2021)

4.     P. Rickhaus, F. de Vries, J. Zhu, E. Portolés, G. Zheng, M. Masseroni, A. Kurzmann, T. Taniguchi, K. Wantanabe, A. H. MacDonald, T. Ihn, and K. Ensslin, “Correlated Electron-Hole State in Twisted Double-Bilayer Graphene”, Science 373, 1257 (2021)

5.     Annika Kurzmann, Yaakov Kleeorin, Chuyao Tong, Rebekka Garreis, Angelika Knothe, Marius Eich, Christopher Mittag, Carolin Gold, Folkert K. de Vries, Kenji Watanabe, Takashi Taniguchi, Vladimir Fal'ko, Yigal Meir, Thomas Ihn, Klaus Ensslin, «Kondo effect and spin-orbit coupling in graphene quantum dots», Nat. Comm. 12, 6004 (2021)

6.     Chuyao Tong, Annika Kurzmann, Rebekka Garreis, Wei Wister Huang, Samuel Jele, Marius Eich, Lev Ginzburg, Christopher Mittag, Kenji Watanabe, Takashi Taniguchi, Klaus Ensslin, and Thomas Ihn, «Pauli Blockade of Tunable Two-Electron Spin and Valley States in Graphene Quantum Dots», Phys. Rev. Lett. 128, 067702 (2022)

7.     Lisa Maria Gächter, Rebekka Garreis, Chuyao Tong, Max Josef Ruckriegel, Benedikt Kratochwil, Folkert Kornelis de Vries, Annika Kurzmann, Kenji Watanabe, Takashi Taniguchi, Thomas Ihn, Klaus Ensslin, Wister Wei Huang, «Single-shot readout in graphene quantum dots», PRX Quantum 3, 020343 (2022)

8.     Elías Portolés, Shuichi Iwakiri, Giulia Zheng, Peter Rickhaus, Takashi Taniguchi, Kenji Watanabe, Thomas Ihn, Klaus Ensslin, and Folkert K. de Vries, «A Tunable Monolithic SQUID in Twisted Bilayer Graphene», arXiv:2201.13276