Decoherence in a N -qubit solid-state quantum register
Boris Ischi, Michael Hilke, Martin Dubé · Physical Review B · 2005
We investigate the decoherence process for a quantum register composed of $N$ qubits coupled to an environment. We consider an environment composed of one common phonon bath and several electronic baths. This environment is relevant to the implementation of a charge based solid-state quantum computer. We explicitly compute the time evolution of all off-diagonal terms of the register's reduced density matrix. We find that in realistic configurations, ``superdecoherence'' and ``decoherence-free subspaces'' do not exist for an $N$-qubit system. This means that all off-diagonal terms decay, but not faster than ${e}^{\ensuremath{-}q(t)N}$, where $q(t)$ is of the same order as the decay function of a single qubit.