"Combining Coherent and Noise Control:"
'How to Transfer between Arbitrary n-Qubit States by Coherent Control and
Simplest Switchable Noise on a Single Qubit'
We explore reachable sets of open $n$-qubit quantum systems the coherent parts
of which are under full unitary control and that have just one qubit whose unital or
non-unital noise amplitudes can be modulated in time such as to provide an additional
degree of incoherent control. 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. This means one can transform any initial quantum state into
any desired target state. Adding switchable bit-flip noise (unital), on the other hand,
suffices to explore all states majorised by the initial state. We have extended our
optimal control algorithm (DYNAMO) by degrees of incoherent control so that these
unprecedented reachable sets can systematically be exploited for experimental
settings. Numerical results are compared to constructive analytical schemes.