This site does a beautiful job of visualizing otherwise difficult to conceive aspects of quantum mechanics. With their changeable conditions, the applets inspire great curiosity for the layman to inquire more in depth about the presented topics as well as clarification for the a little more advanced physics student. In either case, the applets invite the user to spend ample time with the concepts.The applets are not only very helpful and sound, but also an aesthetically pleasing supplement to any Quantum Mechanics/Modern Physics book. Minor technical flaws overal do not distract from the site's easy to use, instructing applets.
Wave/Particle Duality in Quantum Mechanics This site superbly visualizes the Young slit experiment. The posed question about the reason for the decrease in noise the when more particles have hit the screen guides the reader in the right direction to think of the experiment in a statistical manner.
Propagation of a Free Wavepacket The otherwise difficult to envision propagation and successive spreading of a wavepacket is playfully illustrated here. The only improvement suggestions I have are 1) To enlarge the graph in which the waves are spreading. This way the waves of width 1 and 2 would more clearly show signs of spreading by the time they reach the graph's end in both the probability density as well as in the real part of the wave function. 2) To include the wavepacket's propagation in momentum space as it is so tightly related to configuration space.
Propagation of a Non-Minimal Wavepacket This illustration is an excellent follow up to the previous applet. Not all wavepackets start propagation from their minimum size. The non-minimal wavepacket first contracts in configuration space as the waves with higher frequencies at the trailing edge "catch up" to the bulk of the wave and then spread ahead of the rest.
Steps and barriers This applet smoothly visualized a gaussian wavepacket hitting a step potential under various conditions. The reflection,
interference and transmission are evident and well executed. The user really benefits from the changeability of the energy of the step potential. There is one thing that demands change for the text to be physically sound: The second paragraph should read "When the step height is less or smaller ?" It would also be nice to see what happens when a wavepacket hits a finite barrier of step height less than its particle energy.
Scanning Tunneling Microscope This applet is a fun and thoughtful addition to the previous visualizations as it provides a bridge from theoretical to measurable physics. I suggest explaining what is meant by the "sample." The electric green color made me think of GAK, which the sample is not.
Spelling and grammar need some attention to make the texts a non- distracting, flawless reading. A better compromise between tex box size and applet size could also be found. When manipulating an applet would be moe helpful to be able to read the whole featured explanation text rather than merely one sentence at a time.