  It is intuitively imagined that the energy of a classical object always takes
continues values and can hardly be confined to discrete ones like the energy
levels of microscopic systems. Here, we demonstrate that such classical energy
levels against intuition can be created through a previously unknown
synchronization process for nonlinearly coupled macroscopic oscillators driven
by two equally strong fields. Given the properly matched frequencies of the two
drive fields, the amplitude and phase of an oscillator will be frozen on one of
a series of determined trajectories like energy levels, and the phenomenon
exists for whatever drive intensity beyond a threshold. Interestingly, the
oscillator's motion can be highly sensitive to its initial condition but,
unlike the aperiodicity in chaotic motion, it will nonetheless end up on such
fixed energy levels. Upon reaching the stability, however, the oscillations on
the energy levels are robust against noisy perturbation.
