  Learning quantum mechanics is challenging, even for upper-level undergraduate
and graduate students. Interactive tutorials which build on students' prior
knowledge can be useful tools to enhance student learning. We have been
investigating student difficulties with the quantum mechanics pertaining to the
double-slit experiment in various situations. Here we discuss the development
and evaluation of a Quantum Interactive Learning Tutorial (QuILT) which makes
use of an interactive simulation to improve student understanding. We summarize
common difficulties and discuss the extent to which the QuILT is effective in
addressing them in two types of courses.
