Identification of Phase Plate Properties Using Photonic Quantum Sensor Networks

Quantum sensor networks (QSNs) have been widely studied for their potential of precise measurements. While most QSN research has focused on estimating continuous variables, recent studies have explored discrete-variable estimation. Here, we propose a method for high-precision identification of phase plate properties using a photon-based QSN, which is categorized as discrete-variable estimation. We consider an interaction of a single photon with $N$ phase plates. There are some distinct properties of the phase plates, and we aim to identify such properties. Specifically, we investigate two cases: (i) distinguishing between phase plates that impart uniformly random phases in the range $[0, 2\pi]$ and those that impart the same phase, and (ii) distinguishing between phase plates that impart uniformly random phases in $[0, 2\pi]$ and those that impart phases within a narrower range $[- \delta, \delta]$ ($0< \delta \ll 1$). For this distinction, we consider two approaches: one in which a single photon is prepared in a nonlocal state before interacting with the phase plates, and the other in which the single photon remains in a local state. Our results demonstrate that the nonlocal state enables more precise identification when $N$ is large.