  Scalable quantum computation in realistic devices requires that precise
control can be implemented efficiently in the presence of decoherence and
operational errors. We propose a general constructive procedure for designing
robust unitary gates on an open quantum system without encoding or measurement
overhead. Our results allow for a low-level error correction strategy solely
based on Hamiltonian engineering using realistic bounded-strength controls and
may substantially reduce implementation requirements for fault-tolerant quantum
computing architectures.
