  We present an approach for time-dependent quantum transport based on a
self-consistent non-equilibrium Green function formalism. The technique is
applied to a ballistic carbon nanotube transistor in the presence of a time
harmonic signal at the gate. In the ON state the dynamic conductance exhibits
plasmonic resonant peaks at terahertz frequencies. These vanish in the OFF
state, and the dynamic conductance displays smooth oscillations, a signature of
single particle quantum effects. We show that the nanotube kinetic inductance
plays an essential role in the high-frequency behavior.
