Damping and decoherence of Fock states in a nanomechanical resonator due   to two level systems
  We numerically investigate the decay of initial quantum Fock states and their superpositions for a mechanical resonator mode coupled to an environment comprising interacting, damped tunneling two level system (TLS) defects. The cases of one, three, and six near resonant, interacting TLS's are considered in turn and it is found that the resonator displays Ohmic bath like decay behavior with as few as three TLS's. 
Laura G. Remus, Miles P. Blencowe
cond-mat.mes-hall quant-ph