# Experimental investigation of linear-optics-based quantum target detection

## TL;DR

This paper experimentally compares quantum and classical linear-optics-based target detection, demonstrating a quantum advantage in noisy environments, with potential for further improvement using better detection electronics.

## Contribution

It provides the first experimental demonstration of quantum target detection using linear optics and analyzes the noise limitations compared to classical methods.

## Key findings

- Quantum strategy outperforms classical when SNR > 1/40 (~16dB noise)
- Multiple background photons limit quantum advantage in linear optics
- Potential for near-future quantum advantage with improved detection electronics

## Abstract

The development of new techniques to improve measurements is crucial for all sciences. By employing quantum systems as sensors to probe some physical property of interest allows the application of quantum resources, such as coherent superpositions and quantum correlations, to increase measurement precision. Here we experimentally investigate a scheme for quantum target detection based on linear optical measurment devices, when the object is immersed in unpolarized background light. By comparing the quantum (polarization-entangled photon pairs) and the classical (separable polarization states), we found that the quantum strategy provides us an improvement over the classical one in our experiment when the signal to noise ratio is greater than 1/40, or about 16dB of noise. This is in constrast to quantum target detection considering non-linear optical detection schemes, which have shown resilience to extreme amounts of noise. A theoretical model is developed which shows that, in this linear-optics context, the quantum strategy suffers from the contribution of multiple background photons. This effect does not appear in our classical scheme. By improving the two-photon detection electronics, it should be possible to achieve a polarization-based quantum advantage for a signal to noise ratio that is close to 1/400 for current technology.