Berry phase in open quantum systems: a quantum Langevin equation   approach
  The evolution of a two level system with a slowly varying Hamiltonian, modeled as s spin 1/2 in a slowly varying magnetic field, and interacting with a quantum environment, modeled as a bath of harmonic oscillators is analyzed using a quantum Langevin approach. This allows to easily obtain the dissipation time and the correction to the Berry phase in the case of an adiabatic cyclic evolution. 
Gabriele De Chiara, Artur Lozinski and G. Massimo Palma