Quantum target detection

Quantum target detection forms a particular subset of quantum sensing protocols whereby one's task is to determine whether or not a target is present within some region of interest. The goal is to outperform the corresponding optimal classical protocol, establishing a quantum advantage. Such an advantage arises from phenomena native to quantum mechanics allowing for measurement sensitivities otherwise impossible when one is restricted to purely classical means.

This thesis studies the potential of quantum target detection starting with the quantum illumination protocol and outlining the landscape of potential future research. Later chapters provide theoretical contributions addressing the many challenges associated with quantum illumination, particularly at the microwave, in turn.

Through the study of generic Gaussian sources, we show that maximal entanglement is not strictly necessary to achieve a quantum advantage, significantly reducing the experimental burden of source generation. Microwave operation brings a unique set of experimental challenges regarding source generation, detection and idler storage. These challenges also apply to coherent states for which we provide analyses of true classical benchmarks for the microwave. We study the potential of immediate idler measurement, only storing classical outcomes for later recombination with signal outcomes in post-processing. The effective signal-to-noise ratio is derived, assuming the simulation of a phase-conjugating receiver, which may be readily adapted to include noise from arbitrary measurements. We proceed to study the effect of a non-deterministic noiseless linear amplifier at the detection stage showing a significant improvement in error exponent compared to un-amplified protocols, retaining a quantum advantage. Channel position finding is considered in an attempt to extend quantum illumination to target metrology. We show a quantum advantage across a wide class of states constrained to at most one single photon per mode and study its potential in quantum illumination-based quantum target ranging.