Arbitrary n-Qubit State Transfer Implemented by Coherent Control and   Simplest Switchable Local Noise
  We study reachable sets of open n-qubit quantum systems, whose coherent parts are under full unitary control, by adding as a further degree of incoherent control switchable Markovian noise on a single qubit. In particular, adding bang-bang control of amplitude damping noise (non-unital) allows the dynamic system to act transitively on the entire set of density operators. Thus one can transform any initial quantum state into any desired target state. Adding switchable bit-flip noise (unital) instead suffices to get all states majorised by the initial state. Our open-loop optimal control package DYNAMO is extended by incoherent control to exploit these unprecedented reachable sets in experiments. We propose implementation by a GMon, a superconducting device with fast tunable coupling to an open transmission line, and illustrate how open-loop control with noise switching achieves all state transfers without measurement-based closed-loop feedback and resettable ancilla. 
Ville Bergholm, F.K. Wilhelm and T. Schulte-Herbrueggen
quant-ph