This project improves the teaching of quantum mechanics at all levels of the undergraduate curriculum by exposing students to experiments that concretely illustrate some of the most surprising and abstract features of quantum mechanics. The project develops a set of introductory optics experiments and activity-based curricular materials that provide students with the necessary skills to perform and understand the more advanced quantum mechanics experiments by adapting a series of photon quantum mechanics experiments used at the sophomore and the junior/senior level. Student understanding of quantum interference as well as student attitudes and excitement about quantum mechanics are assessed.
The main objective of this grant was to incorporate single-photon quantum mechanics experiments into the undergraduate physics curriculum and to develop appropriate curricular materials to support these experiments. By incorporating such experiments and curricular materials, we hoped to improve the teaching of quantum mechanics by exposing students to real experiments that concretely illustrate some of the most surprising and abstract features of quantum mechanics. We began by incorporating a series of basic optics experiments to give students the appropriate background knowledge and skills that are necessary to understand and fully appreciate the more advanced quantum-mechanics experiments. Such introductory experiments include quantitative investigations on the polarization of light, diffraction from a single slit, and double-slit interference. Students are also exposed to an "optics playground," where they construct a polarizing Mach-Zehnder interferometer. In addition to these background experiments, we developed a Fourier optics experiment to semi-quantitatively investigate spatial filtering and image reconstruction. This experiment allows students to view and manipulate the (optical) Fourier transform of a square-wave image. By filtering specific spatial frequencies, students can observe how the reconstructed image differs from the original image and then compare their observation to a theoretical prediction. The main quantum experiments begin by first determining that light must be described in terms of photons (a reproduction of the Grangier experiment). In particular, we verify that when a photon is incident on a beam splitter, the photon can either be transmitted or reflected but never both. Once this photon description is established, we then go on to demonstrate an interference pattern after passing through a Mach-Zehnder interferometer. Such experimental results can only be explained if each individual photon simultaneously takes both paths through the interferometer. Such a series of experiments demonstrates the central mystery of quantum mechanics. We first show that each photon can only go one way or the other (never both) at a beam splitter, and then show that each photon must go both ways through the interferometer. This seeming contradiction provides great motivation for students to actually learn how quantum mechanics can predict such strange behavior. The difference between the two experiments lies in where we measure the photons. When we attempt to observe which way the photons travel, we see that they always go one way or the other. But if we do not try to observe which way the photons travel, then they always go both ways. Students respond very positively to these experiments. From a purely subjective standpoint, students are clearly intrigued by the strange results and there is a high level of energy during the quantum portion of the course. More objectively, we administered a short questionnaire that shows that students really do enjoy the experiments and believe that it leads to a better understanding of quantum mechanics. Beyond the experiments that we incorporated into courses, the new quantum optics lab has also served a number of advanced senior research experiments. For example, one student worked through an experimental variant of Bell’s theorem to demonstrate that the nature of reality is not consistent with the concept of local realism. In addition to putting together the experiments and developing the corresponding curricular materials, we also gave a two-day workshop for faculty members who were interested in developing similar experiments at their own institutions. This intensive workshop was designed to allow participants get their hands on the experiments and to provide an overview of how we incorporate such experiments in our classes. Participants were encouraged and given time to develop a plan for how these experiments can be implemented back at their own institutions. A survey demonstrated that the participants overwhelming felt the workshop was very useful. Lastly, we presented our work at both teaching and research conferences and gave a series of colloquia presentations at nearby institutions. We also published a lengthy article in the American Journal of Physics that outlines our incorporation of the quantum experiments into our sophomore-level "modern physics" course. We continue to tweak the spatial filtering setup and plan on writing an article to describe the unique semi-quantitative aspects of this experiment.
