  I consider the role of detection noise in quantum-enhanced metrology in
collective spin systems, and derive a fundamental bound for the maximum
obtainable sensitivity for a given level of added detection noise. I then
present an interaction-based readout utilising the commonly used one-axis
twisting scheme that approaches this bound for states generated via several
commonly considered methods of generating quantum enhancement, such as one-axis
twisting, two-axis counter-twisting, twist-and-turn squeezing, quantum
non-demolition measurements, and adiabatically scanning through a quantum phase
transition. I demonstrate that this method performs significantly better than
other recently proposed interaction-based readouts. These results may help
provide improved sensitivity for quantum sensing devices in the presence of
unavoidable detection noise.
