Long distance quantum illumination and ranging using polarization entangled photon pairs in a lossy environment

TL;DR

This paper demonstrates a robust quantum illumination and ranging scheme using polarization-entangled photon pairs over nearly 1 km in lossy free-space environments, maintaining strong quantum correlations for practical object detection.

Contribution

The study introduces a polarization-entangled photon pair setup for long-distance quantum illumination that remains effective despite high losses and scattering.

Findings

High-visibility polarization entanglement with CHSH parameter S=2.802

Strong quantum correlations observed over 1 km free-space propagation

Robust entanglement recovery after scattering from distant objects

Abstract

Using polarization entangled photon pairs, we demonstrate a robust scheme for quantum illumination and ranging in a lossy environment. Entangled photon pairs are generated in a Sagnac interferometer configuration, yielding high-visibility two-photon polarization entanglement with a measured CHSH parameter of $S =2.802\pm0.002$. One of the photons from the entangled pair is retained as idler and the other one is directed into either of the two paths, namely reference and probe, of which probe is sent toward a distant object through a lossy free-space channel, and the reflected photons are collected after round-trip free-space propagation over distances approaching $1$ km. Remarkably, strong correlations are observed with CHSH values $S >2.6$ even when only a few tens of probe photons are returned, confirming the robustness of polarization entanglement under long-distance free-space propagation. This work reports the robustness of encoding photons in different basis before it is sent towards the object and recovery of polarization entanglement even after a kilometer-scale scattering from the objects, establishing a practical foundation for scalable quantum-assisted object detection and ranging.