A modification of the Holstein-Primakoff transformation is proposed such that
creation and annihilation operators for a bosonic field are rewritten as
operators of a SU(2) algebra. Once it is applied to a quantum Hamiltonian, a
subsequent application of the prescription by Lieb to obtain the classical
limit for spin operators allows one to write efficiently a classical
Hamiltonian for the system. This process is illustrated for the M-atom
Jaynes-Cummings model.Comment: 11 pages, 3 figures, English version of the work published in Anais
do XX ENMC -- Encontro Nacional de Modelagem Computacional e VIII ECTM --
Encontro de Ci\^encias e Tecnologia de Materiais, Nova Friburgo, RJ -- 16 a
19 Outubro 2017 Some errors concerning the Jaynes-Cummings model need to be
fixed