[Paper Review] Introduction to quantum radar

Ricardo Gallego Torromé, Nadya Ben Bekhti-Winkel+1 more|arXiv (Cornell University)|Jun 25, 2020

Quantum Information and Cryptography81 references21 citations

TL;DR

This paper provides a comprehensive, accessible review of quantum radar concepts, focusing on quantum illumination and interferometric radar using entangled photons. It evaluates the feasibility of various quantum radar protocols, highlighting theoretical advantages in noisy environments—such as a 3 dB sensitivity gain over classical radar—but identifies major practical challenges, including microwave entanglement generation, lossy idler storage, and the time-bandwidth problem, which currently prevent realization of functional quantum radar systems.

ABSTRACT

After a brief introduction to the notion of quantum entanglement and quantum correlations, several schemes for a quantum radar based upon the quantum illumination and others protocols are discussed. We review different concepts that have been introduced to overcome several of the inherent difficulties in the implementation of quantum generation and/or detection quantum sensing protocols for RADAR applications. Our review is an up-to date critical presentation of the state of the art, with emphasis in the case by case assessment of the feasibility of the different concepts. We also aim that the review is accessible to non-experts in the field. Hence several appendixes and a technical glossary are included.

Motivation & Objective

• To provide a critical, up-to-date overview of quantum radar concepts for non-experts in quantum optics and radar engineering.
• To assess the practical feasibility of quantum radar protocols, especially quantum illumination, under realistic noise and technological constraints.
• To identify and analyze key theoretical and experimental challenges hindering the implementation of functional quantum radar systems.
• To bridge the gap between quantum optics researchers and classical radar practitioners by clarifying technical concepts and current limitations.
• To evaluate the potential of quantum radar for target detection beyond classical limits, despite current technological barriers.

Proposed method

• Reviews theoretical foundations of quantum entanglement and non-classical correlations relevant to radar applications.
• Analyzes quantum illumination protocols, including Lloyd’s proposal and Gaussian quantum illumination, using quantum Chernoff bounds to quantify sensitivity gains.
• Examines experimental implementations such as Lopaeva et al.’s and England et al.’s direct photon detection experiments, comparing performance with coherent-state illumination.
• Evaluates microwave quantum illumination using Josephson parametric amplifiers (JPAs) and four-wave mixing in birefringent fibers for entangled photon generation.
• Discusses the use of adaptive optics and non-linear processes (e.g., SPDC, SFWM) for generating and manipulating entangled states in continuous variable systems.
• Assesses hybrid protocols and the Maccone-Ren quantum radar scheme, focusing on entanglement-enhanced sensitivity and practical limitations like time-bandwidth product and lossy idler storage.

Experimental results

Research questions

• RQ1 Can quantum illumination provide a measurable sensitivity advantage over classical radar in noisy environments, and what is the magnitude of this advantage?
• RQ2 What are the primary technical barriers—such as loss, bandwidth, or cryogenic requirements—that prevent the realization of practical quantum radar systems?
• RQ3 How do different entanglement generation methods (e.g., SPDC, JPA, four-wave mixing) compare in terms of efficiency, frequency tunability, and suitability for radar applications?
• RQ4 To what extent does the use of entangled states enhance target detection in the presence of Rayleigh fading or environmental noise?
• RQ5 Can hybrid or alternative protocols (e.g., Maccone-Ren, JPA-modulated radar) overcome the limitations of standard quantum illumination for real-world radar deployment?

Key findings

• Quantum illumination provides a theoretical sensitivity advantage of up to 3 dB over coherent-state illumination, as shown by Chernoff bound analysis in Guha and Erkmen’s work.
• Theoretical analysis confirms that entanglement-based radar maintains its advantage even in noisy environments, contrary to classical intuition.
• Practical implementation of Gaussian quantum illumination for radar is deemed impracticable due to stringent requirements on time-bandwidth product and signal-to-noise ratios.
• Microwave quantum illumination using Josephson parametric amplifiers enables partial frequency modulation and range resolution, but requires cryogenic conditions (~7 mK), posing a major engineering challenge.
• Four-wave mixing in birefringent fibers enables entangled photon generation at microwave frequencies without cryogenics, though phase-matching conditions are not fully satisfied.
• The Maccone-Ren protocol offers a path to enhanced sensitivity via entanglement, but practical deployment is limited by the need for high-fidelity entangled state generation and low-loss idler storage.