  Considering non-Hermitian systems implemented by utilizing enlarged quantum
systems, we determine the fundamental limits for the sensitivity of
non-Hermitian sensors from the perspective of quantum information. We prove
that non-Hermitian sensors do not outperform their Hermitian counterparts
(directly couples to the parameter) in the performance of sensitivity, due to
the invariance of the quantum information about the parameter. By scrutinizing
two concrete non-Hermitian sensing proposals, which are implemented using full
quantum systems, we demonstrate that the sensitivity of these sensors is in
agreement with our predictions. Our theory offers a comprehensive and
model-independent framework for understanding the fundamental limits of
non-Hermitian quantum sensors and builds the bridge over the gap between
non-Hermitian physics and quantum metrology.
