Quantum pathology of static internal imperfections in flawed quantum computers

Even in the absence of external influences the operability of a quantum computer (QC) is not guaranteed because of the effects of residual one– and two–body imperfections. Here we investigate how these internal flaws affect the performance of a quantum controlled-NOT (CNOT) gate in an isolated flawed QC. First we find that the performance of the CNOT gate is considerably better when the two–body imperfections are strong. Secondly, we find that the largest source of error is due to a coherent shift rather than decoherence or dissipation. Our results suggest that the problem of internal imperfections should be given much more attention in designing scalable QC architectures.