The Stern-Gerlach experiment has played a central role in the discovery ofspin angular momentum. It can also play a pivotal role in teaching theformalism of quantum mechanics using a concrete example involving afinite-dimensional Hilbert space. Using this context, students can learn abouthow to prepare a specific quantum state starting from an arbitrary state,issues related to the time evolution of the wave function, and quantummeasurement. It can also be exploited to teach students about the distinctionbetween the physical space where one performs the experiment and the Hilbertspace where the state of the system lies and how the information about thestate of the system in the Hilbert space can be exploited to interpret thepossible outcomes of the experiment in the physical space. Students can learnthe advantages of choosing an appropriate basis to make suitable predictionsabout the outcomes of experiments with different arrangements of Stern-Gerlachdevices. This experiment can also help students understand that an ensemble ofidentically prepared systems, e.g., one in a linear superposition of twostationary states, is not the same as a mixture, e.g., in which half of thesystems are in one stationary state and the other half are in the otherstationary state. Here, we discuss investigation of students' difficultiesabout the Stern-Gerlach experiment by giving written tests and interviewingadvanced undergraduate and graduate students in quantum mechanics courses. Wealso discuss preliminary data from two quantum mechanics courses that suggestthat a Quantum Interactive Learning Tutorial (QuILT) related to theStern-Gerlach experiment is helpful in improving students' understanding ofthese concepts.
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