Quantum Sensing Based on Two-photon Interference

Abstract

Quantum sensing exploits quantum phenomena to estimate physical parameters with a precision that can surpass the capabilities of classical approaches. Among the available quantum resources, two-photon interference provides a powerful mechanism for retrieving information about the relative properties of optical probes. However, conventional interference-based sensing schemes are fundamentally limited when photons become distinguishable in the degree of freedom carrying the parameter of interest, resulting in the degradation or complete loss of interference. This thesis investigates how quantum interference can be recovered through measurements that resolve the internal modes of photons, enabling quantum-limited estimation beyond conventional interferometric approaches.
The theoretical foundations of quantum optics and quantum parameter estimation are developed to establish a general framework for analysing two-photon interference as a resource for sensing. The evolution and measurement of single-photon states are described within a unified quantum optical
formalism, which is then connected with classical and quantum estimation theory. This framework reveals how information encoded in the distinguishability of photons can be accessed by resolving the degree of freedom conjugate to the parameter of interest, leading to a general methodology based on inner-mode-resolved two-photon interference. The developed approach is applied to a broad range of quantum sensing problems. Quantum-limited estimation protocols are investigated for frequency shifts, temporal delays, transverse displacements
and transverse momentum differences. The impact of realistic experimental limitations, including finite detector resolution, imperfect measurement configurations, and partial distinguishability, is analysed to determine the achievable precision and operational range of the proposed schemes. Furthermore, the framework is extended to multiple-parameter estimation, including the simultaneous characterization of photonic states and polarization properties, demonstrating the applicability of the underlying principles across different physical degrees of freedom. The results establish a unified perspective on how suitably engineered measurements can overcome the limitations imposed by photon distinguishability. This thesis advances the theoretical understanding of quantum-limited optical sensing and provides practical methodologies for the development of future quantum technologies.

Date of Award	9 Sept 2026
Original language	English
Awarding Institution	University of Portsmouth
Supervisor	Vincenzo Tamma (Supervisor) & Paolo Facchi (Supervisor)