Precision Bounds for Nonlinear Quantum Metrology under Collective Dephasing
Deriving the best achievable estimation precision when N quantum sensors encode a frequency parameter quadratically (nonlinearly) in a Ramsey protocol subject to collective dephasing. Learners see why entanglement gives no advantage under Markovian noise, how temporally correlated noise unlocks a Zeno-regime N^-5/4 scaling, how spin-squeezed states with nonlinear readout reach the asymptotically optimal N^-3/2, and how a two-observable ratio estimator removes noise-induced bias.
2501.00189
Quantum metrology estimates a parameter (here a frequency) more precisely than classical methods by using entanglement, spin squeezing, or interactions among N sensors. Dephasing noise is the main ob…