  A gate-defined quantum dot in bilayer graphene is utilized as a sensitive
electrometer for probing the charge density of its environment. Under the
influence of a perpendicular magnetic field, the charge carrier density of the
channel region next to the quantum dot oscillates due to the formation of
Landau levels. This is experimentally observed as oscillations in the
gate-voltage positions of the Coulomb resonances of the nearby quantum dot.
From the frequency of the oscillations, we extract the charge carrier density
in the channel and from the amplitude the shift of the quantum dot potential.
We compare these experimental results with an electrostatic simulation of the
device and find good agreement.
