  Quantum metrology pursues the physical realization of higher-precision
measurements to physical quantities than the classically achievable limit by
exploiting quantum features, such as entanglement and squeezing, as resources.
It has potential applications in developing next-generation frequency
standards, magnetometers, radar, and navigation. However, the ubiquitous
decoherence in the quantum world degrades the quantum resources and forces the
precision back to or even worse than the classical limit, which is called the
no-go theorem of noisy quantum metrology and greatly hinders its applications.
Therefore, how to realize the promised performance of quantum metrology in
realistic noisy situations attracts much attention in recent years. We will
review the principle, categories, and applications of quantum metrology.
Special attention will be paid to different quantum resources that can bring
quantum superiority in enhancing sensitivity. Then, we will introduce the no-go
theorem of noisy quantum metrology and its active control under different kinds
of noise-induced decoherence situations.
