  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.
