  We propose the manipulation of an isolated qubit by a simple instantaneous
closed-loop feedback scheme in which a time-dependent electronic detector
current is directly back-coupled into qubit parameters. As specific detector
model we employ a capacitively coupled single-electron transistor. We
demonstrate the stabilization of pure delocalized qubit states above a critical
detector-qubit coupling. This electronic purification is independent of the
initial qubit state and is accomplished after few electron jumps through the
detector. Our simple scheme can be used for the efficient and robust
initialization of solid-state qubits in quantum computational algorithms at
arbitrary temperatures.
