  Quantum states in graphene are four-fold degenerate: two fold in spins, and
two fold in valleys.Both degrees of freedom can be utilized for qubit
preparations. In our bilayer graphene quantumdots, we demonstrate that the
valley g-factorgv, defined analogously as the spin g-factorgsforvalley
splitting in perpendicular magnetic field, is tunable by over a factor of 4
from 20 to 90. Wefind that largergvresults from larger electronic dot sizes,
determined from the charging energy.This control is achieved by adjusting
voltages on merely two gates, which also allows for tuning ofthe dot-lead
tunnel coupling. On our versatile device, bipolar operation, charging our
quantum dotwith charge carriers of the same or the opposite polarity as the
leads, can be performed. Dots ofboth polarity are tunable to the first charge
carrier by action of the plunger gate, such that thetransition from an electron
to a hole dot can be observed. By adding more gates, this system caneasily be
extended to host double dots.
