  Extracting useful signals is key to both classical and quantum technologies.
Conventional noise filtering methods rely on different patterns of signal and
noise in frequency or time domains, thus limiting their scope of application,
especially in quantum sensing. Here, we propose a signal-nature-based (not
signal-pattern-based) approach which singles out a quantum signal from its
classical noise background by employing the intrinsic quantum nature of the
system. We design a novel protocol to extract the Quantum Correlation signal
and use it to single out the signal of a remote nuclear spin from its
overwhelming classical noise backgrounds, which is impossible to be
accomplished by conventional filter methods. Our work demonstrates the
quantum/classical nature as a new degree of freedom in quantum sensing. The
further generalization of this quantum nature-based method opens a new
direction in quantum research.
