Quantum Radar: State of the Art and Potential of a Newly-Born Remote Sensing Technology

Quantum technology has already been introduced in many fields, like information processing and communications, and it can potentially change our approach to remote sensing in the microwave and millimeter-wave domain, leading to systems known as Quantum Radars. This new generation of systems does not leverage directly on quantum entanglement, since the latter is too “fragile” to preserve in a noisy and lossy environment,as a radar scenario,but rather on thehigh level of coherence derived from quantum entanglement. Quantum Illuminationisaprocess that exploitsquantum coherence of non-classical states of lightfor remote sensing. It allows for the generation and reception of highly correlatedsignals in the form of optical ormicrowave photons. By correlating the received signal photons with photons entangled with the transmitted ones,it is possible toclearly distinguish, among all the received photons, the echoes from background noise and interferences, boosting to an unprecedented level the sensitivity of remote sensing. Therefore, in principle,it is possible to detect very lowcross-radar section objets, such as stealth targets. Nowadays, very few experiments on Quantum Radar transceivers have been reported. This work aims at summarizing the state of the art of Quantum Radar, introducing its basic working principles, though raising the possible issues of such a technology; secondly, it will point out the possibilitiesof photonics-assisted Quantum Radars, proposing photonics as the ideal field where quantum science and remote sensing can meet for an effective cross-fertilization