Heisenberg Scaling in Many-Body Kinetic Uncertainty Relation via Quantum Feedback
Precision is a central figure of merit for quantum devices, including quantum clocks whose performance is determined by the stability of counting events. Kinetic uncertainty relations set fundamental limits on the precision of such counting observables, showing that their fluctuations cannot be suppressed without increasing the activity of the system. While many-body effects offer a natural route to enhanced performance, it remains unclear how far they can enhance counting precision. In quantum metrology, Heisenberg scaling refers to the suppression of estimation variance as $1/N^2$ with the particle number $N$. This raises the question of whether the fluctuation of counting observables can exhibit an analogous Heisenberg-like $1/N^2$ scaling, but no protocol for achieving it has been established. We establish a protocol that achieves this scaling by applying quantum feedback to a superradiant spin ensemble. Because the superradiant enhancement of activity is transient, the scaling of counting precision becomes achievable only when it is controlled by feedback. We establish this result analytically through a many-body kinetic uncertainty relation and feedback-modified mean-field equations, and show it by numerical simulations. Our results demonstrate that feedback can turn collective dissipation into a resource for Heisenberg scaling of counting precision.