Document Type

Paper

Publication Date

Spring 2026

Abstract

Quantum optics is a specialized area of physics that focuses on using light sources, lenses, mirrors, beam splitters, photon detectors, and other optics equipment to demonstrate the wave-particle nature of light. We take advan tage of the spontaneous down-conversion of photons through a beta-barium borate (BBO) crystal, which splits one higher energy photon into two lower energy photons, conserving energy. We confirm the down conversion in our experiment by precisely aligning two detectors in each of the expected paths of the two down-converted photons and counting the number of coincidences detected, or number of times a photon was detected in both detectors at the same time. Once confirming down-conversion, we set up a Mach-Zehnder Inter ferometer in the path of one of the down-converted photons, in which the beam splitter directs the photon along one of two paths. The paths meet at a second beam splitter, which then directs the photon to one of two detectors. Again, we count the number of coincidences detected and analyze the probability of a coincidence using the second-order coherence function, g(2)(0). These results confirm the particle characteristics of photons. Then, we add a piezo to one leg of the interferometer, which continuously changes the path length of one path. This experiment results in an interference pattern in the number of counts and coincidences, illustrating that the probability of every photon being detected was dependent upon the path length of one path, even if it took the other path. This is supporting evidence for the wave nature of light. Our results, therefore, testify that light has both particle and wavelike properties.

Notes

Course: PHY 330, Advanced Physics Laboratory (Dr. Ken Kiers)

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