  The effective Hamiltonian describing resonant interaction of an ensemble of
identical quantum particles with a photon-free vacuum electromagnetic field has
been obtained with allowance for the second-order terms over the coupling
constant (the Stark interaction) by means of the perturbation theory on the
basis of the unitary transformation of the system quantum state. It has been
shown that in the Markov approximation the effective Hamiltonian terms of the
first-order coupling constant are represented as the quantum Wiener process,
whereas the second-order terms are expressed by the quantum Poisson process. In
the course of investigation it was established that the Stark interaction
played a significant role in the ensemble dynamics, thus influencing the
collective spontaneous decay of the ensemble of an appreciably high number of
identical particles. New fundamental effects have been discovered, i.e., the
excitation conservation in a sufficiently dense ensemble of identical particles
and superradiance suppression in the collective decaying process of an excited
ensemble with the determined number of particles.
