Quantum internal model principle and enhanced disturbance decoupling

In this article we present the Quantum Internal Model Principle which is a consequence of theory of Disturbance Decoupling for quantum systems, the applications of which extends to control of decoherence in open quantum systems. In the process of formulating a disturbance rejection scheme for quantum systems we arrive at the Internal Model Principle for quantum control systems which is first of its kind in the literature. The internal model principle relates the disturbance rejecting control to the model of the environmental interaction and provides conditions under which a quantum system could be successfully and completely decoupled from the environmental interactions. Although the theory of quantum disturbance decoupling is inspired from classical decoupling, the vagaries of quantum mechanics entails non-trivial modifications and redesign of the construction of decoupling control. Such a modification leads to an enhanced disturbance rejection scheme for the classical systems as well.