  Nonlinear effects in mesoscopic devices can have both quantum and classical
origins. We show that a three-Josephson-junction (3JJ) flux qubit in the
_classical_ regime can produce low-frequency oscillations in the presence of an
external field in resonance with the (high-frequency) harmonic mode of the
system, $\omega$. Like in the case of_quantum_ Rabi oscillations, the frequency
of these pseudo-Rabi oscillations is much smaller than $\omega$ and scales
approximately linearly with the amplitude of the external field. This classical
effect can be reliably distinguished from its quantum counterpart because it
can be produced by the external perturbation not only at the resonance
frequency $\omega$ and its subharmonics ($\omega/n$), but also at its
overtones, $n\omega$.
