Quantum-optical sensing and target detection

TL;DR

This thesis investigates quantum-enhanced sensing and target detection, establishing fundamental limits, comparing probe states, and demonstrating advantages of quantum probes like SPES and TMSV over classical states in covert and high-precision scenarios.

Contribution

It provides new quantum limits for covert detection, analyzes phase-insensitive amplifiers, and compares quantum probe states, highlighting the practical advantages of SPES and TMSV in sensing.

Findings

Quantum limits on covert detection error probabilities established.

Quantum probes outperform classical states in gain estimation.

SPES and TMSV show comparable detection performance at low energies.

Abstract

This thesis presents three studies in quantum-enhanced sensing and target detection. The first study explores covert target detection using optical or microwave probes, establishing quantum-mechanical limits on the error probabilities of entanglement-assisted detection methods while maintaining the sender's covertness. It identifies the minimal energy required to preserve covertness and reduce error probabilities, compares two-mode squeezed vacuum probes and coherent states against these limits, and extends the analysis to discriminating thermal loss channels and non-adversarial quantum illumination. The second study focuses on phase-insensitive optical amplifiers, determining the quantum limit on the precision of gain estimation using multimode probes possibly entangled with ancillary systems. It finds that the average photon number and the number of input modes are interchangeable resources for achieving optimal gain sensing precision, contrasting classical probes with quantum probes and highlighting the advantages of the latter, even with single-photon inputs and inefficient photodetection. It also provides a closed-form expression for the energy-constrained Bures distance between two amplifier channels. The third study compares three probe states -- coherent state, two-mode squeezed vacuum (TMSV), and single-photon entangled state (SPES) -- in quantum-enhanced target detection, assessing their performance under signal energy constraints relevant to covert radar sensing. SPES is uniquely positioned as a practical probe due to its non-classical properties after thermal loss and ease of generation. Numerical analysis shows that at low signal energies, the error exponent of TMSV aligns with SPES, indicating comparable detection capabilities and that SPES surpasses the best classical state-the coherent state-in accuracy for certain signal strengths.