  This paper presents a non-Markovian coherent feedback scheme to control
single quantum dot systems. The feedback loop is closed via a quantum tunneling
junction between the natural source and drain baths of the quantum dot. The
exact feedback-controlled non-Markovian Langevin equation is derived for
describing the dynamics of the quantum dot. To deal with the nonlinear memory
function in the Langevin equation, we analyze the Green's function-based root
locus, from which we show that the decoherence of the quantum dot can be
suppressed via increasing the feedback coupling strength. This effectiveness of
decoherence suppression induced by non-Markovian coherent feedback is verified
by an example of single quantum dot systems.
