  Liquid-state NMR quantum computer has demonstrated the possibility of quantum
computation and supported its development. Using NMR quantum computer
techniques, we observed phase decoherence under two kinds of artificial noise
fields; one a noise with a long period, and the other with shorter random
period. The first one models decoherence in a quantum channel while the second
one models transverse relaxation. We demonstrated that the bang-bang control
suppresses decoherence in both cases.
