Freitag Nils M, Reisch Tobias, Chizhova Larisa A, Nemes-Incze Péter, Holl Christian, Woods Colin R, Gorbachev Roman V, Cao Yang, Geim Andre K, Novoselov Kostya S, Burgdörfer Joachim, Libisch Florian, Morgenstern Markus
II. Institute of Physics B, JARA-FIT, RWTH Aachen University, Aachen, Germany.
Institute for Theoretical Physics, TU Wien, Vienna, Austria.
Nat Nanotechnol. 2018 May;13(5):392-397. doi: 10.1038/s41565-018-0080-8. Epub 2018 Mar 19.
Coherent manipulation of the binary degrees of freedom is at the heart of modern quantum technologies. Graphene offers two binary degrees: the electron spin and the valley. Efficient spin control has been demonstrated in many solid-state systems, whereas exploitation of the valley has only recently been started, albeit without control at the single-electron level. Here, we show that van der Waals stacking of graphene onto hexagonal boron nitride offers a natural platform for valley control. We use a graphene quantum dot induced by the tip of a scanning tunnelling microscope and demonstrate valley splitting that is tunable from -5 to +10 meV (including valley inversion) by sub-10-nm displacements of the quantum dot position. This boosts the range of controlled valley splitting by about one order of magnitude. The tunable inversion of spin and valley states should enable coherent superposition of these degrees of freedom as a first step towards graphene-based qubits.
对二元自由度的相干操控是现代量子技术的核心。石墨烯提供了两种二元自由度：电子自旋和能谷。在许多固态系统中已经证明了高效的自旋控制，而对能谷的利用直到最近才开始，尽管尚未实现单电子水平的控制。在此，我们表明将石墨烯范德华堆叠到六方氮化硼上为能谷控制提供了一个天然平台。我们利用扫描隧道显微镜针尖诱导出的石墨烯量子点，并证明通过量子点位置亚10纳米的位移，能谷分裂可在-5至+10毫电子伏特之间调节（包括能谷反转）。这将可控能谷分裂的范围提高了约一个数量级。自旋和能谷态的可调反转应能实现这些自由度的相干叠加，这是迈向基于石墨烯的量子比特的第一步。
