Abstract: Spatially correlated dephasing noise remains a leading source of decoherence in state-of-the-art platforms for quantum-enhanced sensing. In this talk, I will focus on quantum frequency estimation in the presence of fully correlated (“collective”) classical dephasing noise, in both the Markovian and non-Markovian (temporally correlated) regime. In standard Ramsey interferometry settings where the target parameter couples linearly to an observable of N non-interacting qubit probes, a no-go for asymptotic superclassical precision scaling can be established, even if the estimation protocol is augmented with the use of time-dependent dephasing-preserving control. I will outline two strategies for possibly evading such a no-go result. First, I will consider generalized metrological protocols with quadratic signal encoding, and show how, for non-Markovian dephasing, a scaling advantage over the linear 1/N Heisenberg scaling may be reached with initial unentangled spin-coherent states, with further improvement from initial spin-squeezed states. Returning to linear quantum metrology, I will then argue that, for non-Markovian dephasing, the use of time-dependent quadratic control may provide a mechanism for separating the noise from the signal and for achieving a scaling advantage over the no-control case.