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It is shown that a simplified version of the error correction code recently suggested by Shor Phys. Rev. A 52, R2493 (1995) exhibits manifestation of the quantum Zeno effect. Thus, under certain conditions, protection of an unknown quantum state is achieved. Error prevention procedures based on four-particle and two-particle encoding are proposed and it is argued that they have feasible practical implementations.
Vaidman et al. (Sun,) studied this question.