Demonstration of bang-bang control for decoherence suppression with NMR

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 manipulations. We propose to examine various techniques in quantum information processing under noisy environment. A concrete example in which a qubit under artificially generated noise is considered. It is shown both theoretically and experimentally that bang-bang control employing multiple short pulses suppresses decoherence. We demonstrate this using an NMR quantum computer and verify the validity of the theory.