Low density limit: Without rotating wave approximation

In the present paper we investigate the low density limit of a quantum “System + Reservoir” model in which the temperature is finite and the Hamiltonian of the system has a discrete spectrum. It is proved that the matrix elements of the time evolution operator, with a time rescaling and some proper choice of collective vector, tends to matrix elements of a solution of a quantum stochastic differential equation driven by a quantum Poisson process.