  Here we investigate high frequency AC transport through narrow graphene
nanoribbons with topgate potentials that form a localized quantum dot. We show
that as a consequence of the finite dwell time of an electron inside the
quantum dot (QD), the QD behaves like a classical inductor at sufficiently high
frequencies \omega\gtrsim50 GHz. When the geometric capacitance of the topgate
and the quantum capacitance of the nanoribbon are accounted for, the admittance
of the device behaves like a classical serial RLC circuit with resonant
frequencies \omega\sim100-900 GHz and Q-factors greater than 10^{6}. These
results indicate that graphene nanoribbons can serve as all-electronic
ultra-high frequency oscillators and filters thereby extending the reach of
high frequency electronics into new domains.
