  Experimental validation and control of quantum traits for an open quantum
system are important for any quantum information purpose. We consider a
traveling atom qubit as a quantum memory with adjustable velocity inside a
leaky cavity, adopting a quantum witness as a figure of merit for quantumness
assessment. We show that this model constitutes an inherent physical instance
where the quantum witness does not work properly if not suitably optimized. We
then supply the optimal intermediate blind measurements which make the quantum
witness a faithful tester of quantum coherence. We thus find that larger
velocities protect quantumness against noise, leading to lifetime extension of
hybrid qubit-photon entanglement and to higher phase estimation precision.
Control of qubit motion thus reveals itself as a quantum enhancer.
