The importance of level statistics for the decoherence of a central spin   due to a spin environment
  We study the decoherence of a central spin-1/2 due to a closed environment composed of spin-1/2 particles. It is known that a frustrated spin environment, such as a spin glass, is much more efficient for decoherence of the central spin than a similar size environment without frustration. We construct a Hamiltonian where the degree of frustration is parametrized by a single parameter $\kappa$. By use of this model we find that the environment can be classified by two distinct regimes with respect to the strength of level repulsion. These regimes behave qualitatively different with respect to decoherence of the central spin and might explain the strong enhancement of decoherence observed for frustrated environments. 
H{\aa}kon Brox, Joakim Bergli, Yuri M. Galperin
quant-ph cond-mat.mes-hall