Quantum sensing enhanced by adaptive periodic quantum control

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.