Quantum Measurement Encoding for Quantum Metrology

Preserving the precision of the parameter of interest in the presence of environmental decoherence is an important yet challenging task in dissipative quantum sensing. In this work, we study quantum metrology when the decoherence effect is unraveled by a set of quantum measurements,dubbed quantum measurement encoding. In our case, the estimation parameter is encoded into a quantum state through a quantum measurement, unlike the parameter encoding through a unitary channel in the decoherence-free case or trace-preserving quantum channels in the case of decoherence. We identify conditions for a precision-preserving measurement encoding. These conditions can be employed to transfer metrological information from one subsystem to another through quantum measurements. Furthermore, postselected non-Hermitian sensing can also be viewed as quantum sensing with measurement encoding. When the precision-preserving conditions are violated in non-Hermitian sensing, we derive a universal formula for the loss of precision.