Quantum illumination with a light absorbing target

TL;DR

This paper investigates quantum illumination for detecting absorbing targets, showing that absorption can enhance detection efficiency and that quantum advantage persists under certain conditions, with optimal states identified.

Contribution

It models a realistic absorbing target in quantum illumination and analyzes the impact on detection performance using Chernoff bounds, highlighting absorption effects on quantum advantage.

Findings

Absorption can improve detection efficiency in quantum illumination.

Quantum advantage persists despite finite absorption levels.

TMSV state's advantage diminishes with increasing absorption.

Abstract

In a quantum illumination (QI) protocol, the task is to detect the presence of the target which is typically modelled by a partially reflecting beam splitter. We analyze the performance of QI when the target absorbs part of the light that falls on it, thereby making the scenario more realistic. We present an optical setup that models a target with these characteristics and explore its detectability in the quantum domain in terms of the Chernoff bound (CB). For an idler-free setup, we use the coherent state for QI while the two mode squeezed vacuum (TMSV) state is employed in the signal-idler scheme. In both the cases, we report an absorption-induced enhancement of the detection efficiency indicated by a lowering of CB with increasing amounts of absorption. Interestingly, we show that in the presence of absorption, a more intense thermal background can lead to target detection with enhanced efficiency. Moreover, we observe that the quantum advantage persists even for finite amounts of absorption. However, we find that the quantum advantage offered by TMSV decreases monotonically with absorption, and becomes vanishingly small in the high absorption regime. We also demonstrate the optimality of both the coherent and the TMSV states in their respective setups (idler-free and signal-idler) in the limit of low reflectivity and absorption.