Realizing the optimal measurement scheme for an SU(1,1) interferometer in ab initio phase estimation
Phys. Rev. A 111, 063711 – Published 26 June, 2025
DOI: https://doi.org/10.1103/rv9m-n7px
Abstract
In phase estimation via quantum interferometry, measurement precision is governed by the quantum state and the measurement strategy. Nonlinear SU(1,1) interferometers prepare entangled states that have been shown to enable Heisenberg-limit precision. In previous work, we developed the optimal measurement scheme, which saturates the ultimate limit in ab initio phase estimation, avoiding the issue of ambiguity. However, realizing this scheme is highly nontrivial and involves measurements beyond the photon-number operator. In this study, we propose a probabilistic measurement scheme capable of realizing the optimal measurement scheme with a success rate of 50% through postselection. This method allows us to achieve Heisenberg-scaling precision but it is suboptimal with respect to saturation of the quantum Cramér-Rao bound. It utilizes projection synthesis by introducing an ancillary optical mode prepared in a superposition state, combined with standard photon-number-resolving detection. This approach provides insights into the physical realization of optimal measurement strategies in nonlinear interferometers, with implications for quantum precision measurement in general.
