Universal destabilization and slowing of spin transfer functions by a   bath of spins
  We investigate the effect of a spin bath on the spin transfer functions of a permanently coupled spin system. When each spin is coupled to a seperate environment, the effect on the transfer functions in the first excitation sector is amazingly simple: the group velocity is slowed down by a factor of two, and the fidelity is destabilized by a modulation of |cos Gt|, where G is the mean square coupling to the environment. 
Daniel Burgarth and Sougato Bose