Quantum-optical sensing and target detection

• Main Author: Tham, Guo Yao
• Other Authors: Gu Mile
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Physics; Quantum information; Quantum illumination; Quantum metrology; Quantum sensing; Quantum optics; Quantum channel discrimination; Hypothesis testing
• Online Access: https://hdl.handle.net/10356/180628
• Institution: Nanyang Technological University

This thesis encompasses three pivotal studies in the realm of quantum-enhanced sensing and target detection, each addressing unique aspects of quantum optics and information. The first study delves into covert target detection using optical or microwave probes. It establishes quantum-mechanical limits on the error probability performance of entanglement-assisted target detection, ensuring the sender's covertness from an adversary. This research outlines the minimum energy requirement for maintaining covertness while achieving significant error probability reduction. It compares the efficacy of two-mode squeezed vacuum probes and Gaussian-distributed coherent states against these limits and also extends to quantum limits in discriminating thermal loss channels and non-adversarial quantum illumination. The second study focuses on phase-insensitive optical amplifiers, fundamental in both theoretical and practical applications. It identifies the quantum limit of precision in estimating the gain of such amplifiers using multimode probes, possibly entangled with an ancillary system. Remarkably, it finds the average photon number N and the number of input modes M to be interchangeable resources for optimal gain sensing. The study compares classical probes with quantum probes, highlighting the advantages of the latter, even with single-photon probes and in cases of inefficient photodetection. It also presents a closed-form expression for the energy-constrained Bures distance between two amplifier channels. The third study compares three different probe states - coherent state, two-mode squeezed vacuum (TMSV), and single-photon entangled state (SPES) - in quantum-enhanced target detection. It characterizes their performance under signal energy constraints, relevant in applications like covert radar sensing. The study uniquely positions SPES as a feasible physical probe for its non-classical properties post thermal loss channel and ease of generation. Through numerical analysis, it demonstrates that for low signal energy, the error exponent of TMSV aligns with SPES, suggesting comparable target detection capabilities. Moreover, SPES shows superior accuracy over the best classical state, the coherent state, for certain signal strengths. Collectively, these studies contribute to the development of a comprehensive understanding of quantum sensing limits and the efficacy of various quantum probe states, paving the way for advancements in quantum metrology and related applications.