A quantum system with finite degrees of freedom can simulate a composite of a system and its environment if the state of the hypothetical environment is randomized by external manipulation. We propose to examine various techniques in quantum information processing in virtual noisy environment with two concrete examples. One simulates phase decoherence of a single qubit in a transmission line, and the other does in a quantum memory. In both cases, the bang-bang control, a typical example of useful techniques employed in quantum information processing, is observed to be effective to suppress decoherence.

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