# Interaction-free measurement study as a quantum channel discrimination problem

## TL;DR

This paper models interaction-free measurement as a quantum channel discrimination problem using quantum Zeno effect, analyzing probabilities of photon loss and error, and finds optimal states and conditions for perfect detection.

## Contribution

It introduces a quantum channel framework for interaction-free measurement, providing minimum error and loss probabilities, and explores the role of quantum correlations in the process.

## Key findings

- Perfect detection as N approaches infinity with zero loss and error
- Single photon input state is optimal over entangled states for minimizing loss and error
- The analysis technique can be applied to other quantum measurement scenarios

## Abstract

Interaction-free measurement (IFM), just as its name implies, can enable one to detect an object without interacting with it, i.e., substantially reducing the damage to the object. With the help of quantum channel theory, we investigate the general model of "quantum-Zeno-like" IFM, whose optics setup is a Mach-Zehnder like interferometer utilizing the quantum Zeno effect, where the object to be detected is semitransparent and the interrogation cycle number $N$ is finite. And we define two important probabilities $P_{\rm loss}$ and $P_{\rm error}$ to evaluate the IFM process, which describe the photon loss rate and the error of discriminating the presenece/absence of the object respectively. The minimum values of these two probabilities and the corresponding initial input states to reach them are attained via this model. And we find that when the interrogation cycle $N$ approaches infinity, the object can be perfectly detected, where the minimum values of these two probabilities are both zero and the initial input state to reach them becomes the same state $|1\rangle$ in our system. In addition, we also study whether quantum correlation can benefit IFM or not, but the answer is no, in the sense that the entangled photon input state cannot minimize $P_{\rm loss}$, $P_{\rm error}$ more than single photon input state. Our work provides principal theoretic support for the practical realization of IFM and the employed analysis technique can be applied to other quantum facilitating scenarios.