Optimal Dynamical Decoherence Control of a Qubit
  A theory of dynamical control by modulation for optimal decoherence reduction is developed. It is based on the non-Markovian Euler-Lagrange equation for the energy-constrained field that minimizes the average dephasing rate of a qubit for any given dephasing spectrum. 
Goren Gordon, Gershon Kurizki, Daniel A. Lidar