  The strong coupling regime is observed in a system of two-dimensional
electrons whose cyclotron motion is coupled to an electro-magnetic mode in a
Fabry-Perot cavity resonator. The Rabi splitting of eigenfrequencies of coupled
motion is observed both in the cavity reflection spectrum and ac current of
electrons, the latter probed by measuring their bolometric photoresponse.
Despite the fact that similar observations of the Rabi splitting in
many-particle systems have been described as a quantum-mechanical effect, we
show that the observed splitting can be explained completely by a model based
on the classical electrodynamics.
