Decoherence of a Superposition of Macroscopic Current States in a SQUID
  We show that fundamental conservation laws mandate parameter-free mechanisms of decoherence of quantum oscillations of the superconducting current between opposite directions in a SQUID -- emission of phonons and photons at the oscillation frequency. The corresponding rates are computed and compared with experimental findings. The decohering effects of external mechanical and magnetic noise are investigated. 
E. M. Chudnovsky and A. B. Kuklov