posted on 2021-01-15, 19:04authored byChuyao Tong, Rebekka Garreis, Angelika Knothe, Marius Eich, Agnese Sacchi, Kenji Watanabe, Takashi Taniguchi, Vladimir Fal’ko, Thomas Ihn, Klaus Ensslin, Annika Kurzmann
Quantum
states in graphene are 2-fold degenerate in spins, and
2-fold in valleys. Both degrees of freedom can be utilized for qubit
preparations. In our bilayer graphene quantum dots, we demonstrate
that the valley g-factor gv, defined analogously
to the spin g-factor gs for valley splitting
in a perpendicular magnetic field, is tunable by over a factor of
4 from 20 to 90, by gate voltage adjustments only. Larger gv results from larger electronic dot sizes,
determined from the charging energy. On our versatile device, bipolar
operation, charging our quantum dot with charge carriers of the same
or the opposite polarity as the leads, can be performed. Dots of both
polarities are tunable to the first charge carrier, such that the
transition from an electron to a hole dot by the action of the plunger
gate can be observed. Addition of gates easily extends the system
to host tunable double dots.