Manipulating Two-Photon Interference Using Metasurfaces

Abstract

Interference experiments like the light and electron double-slit are crucially important to quantum mechanics since they illustrate the core principle of wave-particle duality, by demonstrating the wave-like aspect of particle phenomena. In such experiments, a device is typically required to manipulate the particle-wave dual phenomenon, producing controllable interference.

Metasurfaces, with their highly flexible configurability, can serve as more versatile versions of such devices. They are powerful tools capable of modulating a broader category of effects beyond classical interference, such as the quantum Hong-Ou-Mandel (HOM) effect. The HOM effect is caused by interference taking place not between coherent waves from distinct sources which intersect in real space, but rather between parallel processes indistinguishable to the measurement apparatus. Existing research has highlighted the outsized importance of measurement in HOM interferometry, by showing that the occurrence of process interference depends only on indistinguishability at the detectors and nowhere else.

We are therefore interested in how quantum measurement occurs in HOM, and how metasurfaces can be used to enhance the HOM effect. In this thesis, we extend a formulation of quantum trajectory theory in two-eigenstate systems to 𝑁-state systems, producing a three-state formalism which serves as a possible description of coincidence pair detection in HOM experiments. We then develop an analytic model of polarisation HOM interferometry capturing both the width and the 𝑔₂ ratio of the HOM dip; finally, we design and fabricate a metasurface that exhibits polarisation filtering with respect to two-photon coincidence, whereupon HOM photon bunching occurs only at select metasurface orientations relative to photon polarisation.

Our three-state quantum state collapse model offers a promising explanation for how state measurement takes place in an HOM interferometer, where the interferometer output is a superimposition of three two-photon eigenstates. Meanwhile, our interferometer model and experiments provide evidence of successful polarisation filtering in HOM interferometry.

Date of Award	2025
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Jensen Tsan Hang LI (Supervisor)