  Unique properties of multimode non-Hermitian lattice dynamics can be utilized
to construct exponentially sensitive sensors. However, the impact of noise
remains unclear, which may severely degrade their sensitivity. We analytically
characterize and highlight the impact of loss and gain on the sensitivity
revival and stability of non-Hermitian sensors. Defying the general belief that
the superiority of quantum sensing will vanish in the presence of loss, we find
that by proactively tuning the loss, the exponential sensitivity can be
surprisingly regained when the sensing dynamics is stable. Furthermore, we
prove that gain is crucial to fully revive the ideally exponential sensitivity
and to ensure the stability of non-Hermitian sensing by making a balanced loss
and gain. Our paper opens a way to significantly enhance the sensitivity by
proactively tuning the loss and gain, which may promote future quantum sensing
and quantum engineering.
