  Using a single quantum probe to sense other quantum objects offers distinct
advantages but suffers from some limitations that may degrade the sensing
precision severely, especially when the probe-target coupling is weak. Here we
propose a strategy to improve the sensing precision by using the quantum probe
to engineer the evolution of the target. We consider an exactly solvable model,
in which a qubit is used as the probe to sense the frequency of a harmonic
oscillator. We show that by applying adaptive periodic quantum control on the
qubit, the sensing precision can be enhanced from 1/T scaling with the total
time cost T to 1/T^{2} scaling, thus improving the precision by several orders
of magnitudes. Such improvement can be achieved without any direct access to
the oscillator and the improvement increases with decreasing probe-target
coupling. This provides a useful routine to ultrasensitive quantum sensing of
weakly coupled quantum objects.
