Investigating and improving student understanding of quantum mechanics in the context of single photon interference

Single photon experiments involving a Mach-Zehnder interferometer can illustrate the fundamental principles of quantum mechanics, e.g., the wave-particle duality of a single photon, single photon interference, and the probabilistic nature of quantum measurement involving single photons. These experiments explicitly make the connection between the abstract quantum theory and concrete laboratory settings and have the potential to help students develop a solid grasp of the foundational issues in quantum mechanics. Here we describe students’ conceptual difficulties with these topics in the context of Mach-Zehnder interferometer experiments with single photons and how the difficulties found in written surveys and individual interviews were used as a guide in the development of a Quantum Interactive Learning Tutorial (QuILT). The QuILT uses an inquiry-based approach to learning and takes into account the conceptual difficulties found via research to help upper-level undergraduate and graduate students learn about foundational quantum mechanics concepts using the concrete quantum optics context. It strives to help students learn the basics of quantum mechanics in the context of single photon experiment, develop the ability to apply fundamental quantum principles to experimental situations in quantum optics, and explore the differences between classical and quantum ideas in a concrete context. We discuss the findings from in-class evaluations suggesting that the QuILT was effective in helping students learn these abstract concepts.

Figure 1

MZI setup with a phase shifter in the $U$ path.

Figure 2

MZI setup with beam splitter 2 (BS2) removed.

Figure 3

MZI setup with an additional detector placed in the $L$ path.

Figure 4

Reflection of light at an air-glass interface.

Figure 5

Screen shot of the computer simulation of a large number of single photons propagating through the MZI. Simulation developed by Albert Huber.

Figure 6

MZI setup with beam splitter 2 (BS2) inserted (left) and MZI setup with beam splitter 2 (BS2) removed (right).

Figure 7

Screen shot of the computer simulation in which an additional detector (blue device) is placed in one of the paths of the MZI. Simulation developed by Albert Huber.