  Instruction in quantum mechanics is becoming increasingly important as the
field is not only a key part of modern physics research, but is also important
for emerging technologies. However, many students regard quantum mechanics as a
particularly challenging subject, in part because it is considered very
mathematical and abstract. One potential way to help students understand and
contextualize unintuitive quantum ideas is to provide them opportunities to
work with physical apparatus demonstrating these phenomena. In order to
understand how working with quantum experiments affects students' reasoning, we
performed think-aloud lab sessions of two pairs of students as they worked
through a sequence of quantum optics experiments that demonstrated
particle-wave duality of photons. Analyzing the in-the-moment student thinking
allowed us to identify the resources students activated while reasoning through
the experimental evidence of single-photon interference, as well as student
ideas about what parts of the experiments were quantum versus classical. This
work will aid instructors in helping their students construct an understanding
of these topics from their own ideas and motivate future investigations into
the use of hands-on opportunities to facilitate student learning about quantum
mechanics.
