Dynamical Suppression of the Decoherence in Quantum Registers

Abstract

Quantum computers that are designed to be perfectly isolated from their environments are in principle, able to solve hard, computationally demanding problems more powerfully than conventional classical computers [1] can. For a real quantum system, however, one can not completely neglect the interaction with its environment. This interaction causes the problem known as decoherence, which corrupts the information stored in the quantum system and produces wrong outputs. To perform a quantum computation we must prepare qubits in a proper initial state and keep them free from interactions that lead to noise and decoherence. Thus, we have to overcome such difficulties to realize practical quantum computers. There have been proposals for more realistic quantum computers. One is to use error-correcting codes encoded in a linear subspace of the total Hilbert space in such a way that errors induced by the interaction with environment can be detected and corrected [2]. Another is to use the error-avoiding codes that are barely corrupted rather than states that can be easily corrected. These error-avoiding codes can be constructed by building a nontrivial subspace of the total Hilbert space that allows a weaker correlation with the environment than the remaining part of the Hilbert space does [3]. Alternatively, recent works [4,5] have demonstrated that