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This set of applets features illustrations of quantum mechanics through interactive animations in the following domains : Young interference fringes - wavepacket propagation - linear superposition of eigenstates (including coherent states of the harmonic oscillator) - nuclear magnetic resonance.
I don't know much about quantum mechanics but, after reviewing these wonderful websites I'm willing to take a chance and learn a little more.
Time spent reviewing site:
13 years ago
Having had a first course in undergraduate quantum mechanics I found Manuel Joffre?s wave mechanics physlets to be at most supplementary in nature but at the same time rather enlightening. The wave-particle duality physlet provides a simulation of the well known double slit experiment. The simulation provides two windows. The first window serves as a backdrop revealing the interference pattern that characterizes the wave behavior of particles passing through a two slit barrier. The second window serves as a histogram for each shot registered at a particular channel/detector on the backdrop. The author does well in asking the user to make qualitative and quantitative assessments as to why the relative noise in the per channel histogram decreases with sample size. This really forces the all important notion of statistical procedure associated with quantum mechanics.
In this double slit simulation, the user may vary two aspects of the experiment: the rate at which particles are fired and the number of fringes to be observed. Some comments might be in order concerning the option for fringe variation. When a double slit experiment is performed in the laboratory, there are certain parameters that must be varied to produce a different number of fringes. Having presented the option for fringe variation in the simulation, it seems natural to provide some instructional comments as to why fringe variation is possible and how it relates to wave theory and experiment.
In the second physlet, Joffre presents a simulation of the propagation of a free wave packet in a dispersive medium. The simulation provides an excellent visualization of the spreading /dispersion of a wavepacket as it propagates through space. As in the double slit simulation,
this simulation has a dual window presentation. The simulation allows the user to toggle between two different representations of the same wave packet as it moves and disperses through space. The first representation is the probability density associated with the wave packet in configuration space. The second representation is the actual physical wave packet itself or the real part of the packets wave function. By toggling between these two representations the user may develop some intuition as to how a probability density in configuration space relates to the physical propagation/dispersion of a wave packet in space. In short, this dual representation offers an excellent opportunity to develop some physical interpretation of a probability density. The author offers some instructional comments concerning the spreading of the wave packet and its probability density in momentum space. While the comments are instructive, perhaps a third representation of the wave packet in momentum space would be most enlightening. In conjunction with the configuration space and real/physical representations , a third representation in momentum space might allow the user to form a more complete picture of the motion of a wave packet and its associated probability densities.
The next of Joffre?s simulations presents a particle of fixed energy relative to potential steps and barriers of various energies. In the case of potential steps the user may vary the step potential and then observe the differences in transmission and reflection probabilities. Probability densities are plotted versus position. The simulation is extremely effective in conveying the idea of how step potentials of various energies affect probabilities of reflection/transmission. In the case of finite potential barriers,
the user may vary only the barrier width and not the barrier height. This is somewhat unfortunate as both barrier height and barrier width determine transmission/reflection probabilities. This dual dependence on height and width seems to be obscured by restricting the users ability to vary only barrier width.
The final simulation in this wave mechanics applet brings us back tothe laboratory with an interactive demonstration of the scanning tunneling microscope (STM). Here, the user traces out the surface of some sample by varying the height of the STM. As the STM traverses across the surface of the sample, electrons tunnel into the microscope?s tip through a Coulomb potential due to the sample?s nuclei and thus generate a measurable current. The user has the task of keeping the measured current constant by varying the height of the STM as it moves across the sample. The interactive nature of this simulation gives the user a good idea of how an STM works and what it measures. What seems to be lacking here are some contextual comments on how the measurements might be interpreted and the overall purpose and usefulness of the STM. More on the STM, however, may by be found in the last segment of this wave mechanics applet. This last segment also contains some interesting biographical sketches of quantum mechanics? most well known pioneers.
In summary, the simulations in this wave mechanics applet do much to enhance the users intuition of some key concepts in quantum mechanics. The dual representations in both the double slit and wave packet simulations are most revealing in their presentation of probability densities, a cornerstone of quantum mechanics. To make a final criticism,
the author might have done better in providing some textual instruction; the simulations seem to have been presented in a sort of vacuum where key concepts might be missed for lack of textual underscore.
13 years ago
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.
13 years ago
These are excellent tools to visualize the basic postulates of Quantum Mechanics. The physical observables demonstrated in the applets are well chosen and allow for rapid serial imprinting of the basics of the theory. I believe that student brain time devoted to insufficient mental models of QM is better served by something like these applets which allow the mind to jump an abstraction layer conceptually. This is a good, non-mathematical starting point for QM.
All the remarks that went with the applets were well written and did teach me new some new physics I had not known about. The only thing I could think to improve would be to specify in the wave packet applet whether or not the wave packet is the minimum uncertainty (Gaussian).
13 years ago
This review of Quantum Physics Online (English Version) covers only the section on wave mechanics. I am a junior undergraduate physics major who has completed a course in modern physics, and I have also been exposed to material generally covered in the first few chapters of an undergraduate quantum mechanics text. My response to this site is extremely positive. The animations concerning both the wave-packet propagation and the steps and barriers clearly illustrate concepts that I had not yet been able to clearly visualize. When I take a quantum mechanics course in the fall and will be more actively studying the mathematics of the subject, I intend on returning to this site for a better-informed pass at the wave mechanics applets, as well as the additional material of the site. Comments concerning the specific material reviewed follow:
Wave-particle duality in a Young slit experiment: I found the animation an excellent representation of the particle-wave slit experiment and was reminded of Feynman scratching out probability curves on his blackboard. I cranked up the rate of the ?lumps? being fired and watched as the curves on the histogram smoothed out to the nearly continuous distributions expected. Simple and very nice.
Propagation of a wave packet: Having scratched my head more than once trying to visualize a ?wave-packet propagating through space?, this applet and some re-reading of textbook material helped me to make some headway on this subject, at least two-dimensionally. I liked that one could specify to watch either the absolute square of the wave function or the real part of the wave function. That the parts of the wave-packet with the greater momentum will propagate faster causing spreading of the wave-packet makes sense when you can watch it happen. I like the option of varying the width (from .5,
1,2) of the wave-packet, assuming that the numbers .5,1,2 correspond to relative widths. This variable ?width? isnice to show that the more localized the packet is initially, the quicker it spreads out in space due to the correlation of increased localization and increased uncertainty in momentum. That the parts of the packet with larger momentums would propagate with larger velocities is nicely seen, though I would prefer to see the animation progress a bit longer than it does. Quibbles.
Propagation of non-minimal wave-packets: Just a variation on the previous, excellent wave-packet applet. The wave-packet localizes and then spreads due, as I have read, to the different initial configuration of momenta in the packet. I have also read that outside measurements will collapse a wave-packet, only for the wave-packet to then spread out or ?grow? with time, collapsing again at each additional measurement. How exactly is this phenomenon related to the non-minimal wave-packet portrayed in this applet?
Steps and Barriers: This is the section for which I have the least exposure and understanding. Again, the animation of quantum tunneling appears to be a wonderful treatment of the subject, but since I am not versed in the mathematics of the phenomenon, in my eyes it still smacks of witchcraft, something I hope that will pass with further exposure. Varying the step size to watch the relative amount of the wave reflected and transmitted is a very instructive exercise, and I look to revisit this applet in the near future when I am better armed.
Scanning tunneling microscope: Our excellent electronics instructor here at Humboldt State has spoke on this topic a few times,
and this applet reflects exactly what I have already learned on the subject (on a relatively qualitative level). The applet provides a nice, fairly qualitative look at the subject, and the interactive part is instructive--calling it a game might be a bit of a stretch.
I applaud the design and operation of the applets. While they were fairly sizable, the load time on my 56K modem was only about ten seconds?well worth the brief wait. There were a few typos noticed, and the brief encroachment of French on the English site (e.g. barriere). The author has obviously paid great attention to detail throughout, both in the programming and in the physics. I offer only my compliments.
13 years ago
The most admirable aspect of this site is that it provides a certain amount of visual elucidation and thus inspiration to the novice quantum mechanic. It is easy to feel like quantum mechanics is a vast collection of unrelated mathematical abstractions when one first embarks on the time-honored set of introductory wave mechanics problems (the particle in a box, particle incident on a step potential, harmonic oscillator etc?). This site illustrates every introductory wave mechanics problem I had previously encountered and several I had not. While the lack of associated text and derivation makes this site unsuitable as a stand alone educational tool it did give many of these problems, which were heretofore vague and abstract, a more visual and concrete significance, and a sense of coherence which I found to be quite appealing. The material presented on this site is primarily at or above my current level of competence in the field of wave mechanics and partial differential equations, but with that disclaimer, I could find no flaws in the material presented. My favorite applet was the particle incident on a step potential barrier. If memory serves most texts put forth a similar problem to describe the transmission probability in which the particle is described by a completely delocalised wave function (&Delta x = infinity). In the applet the particle is described by a function with finite uncertainties in momentum and position. I found that the treatment given in the applet provided a more intuitive sense of transmission of a particle through a barrier, and when time permits I would like to work through the problem for myself. I also enjoyed the applet depicting the double potential well,
but further rumination is needed before I can make any reasonably intelligent commentary on it. In summation I would say that this site is the first to have truly convinced me that Java can play an important role in the teaching of physics, and I intend to return to it to further my own understanding of the subject. My congratulations are extended to its authors.
The site is technically well constructed. The Java applets are masterfully done: plots are clearly labeled and easy to read, all functions are straightforward and easy to use, and the presentation is professional and aesthetically appealing. The only drawbacks I could identify were a handful of typographical errors and the daunting size of the Java applets. The average applet size appeared to be in the neighborhood of 150k, which produced a 10 to 30 second delay on the university computers. I shudder to think how long they would have taken me to load through the 28.8 modem on my home computer
13 years ago
More vital than a book full of equations and physical laws, is the imagination of the physicist. For it is our imagination and physical intuition that lead us to new discoveries. Web pages such as this one help students see, and therefore be able to better imagine the world of quantum mechanics. The beauty of java applets is their ability to show experiments that are difficult, or even impossible to reproduce in the class room. For example, the applet displaying the spreading of the wave packet shows students something they could never see in real life by showing not only the way the packet spreads over time, but the real AND IMAGINARY components of the wave. Illustrations such as these simultaneously help the student understand the situations quantum mechanics deal with, and hopefully spark their imagination as well. The customizable nature of the applets transforms the simulations into virtual experiments, allowing the students to put their new knowledge to work. They can gain a wonderfull intuition about the various systems by playing with the different variables. With all this in mind, it is important to remember that the applets alone cannot do the full job of teaching quantum mechanics. No matter how interactive they are, they are still limited to the boundaries of their program. As a result they can never answer all the questions and address all the concerns of prospective students. They must retain their position in life as a teaching tool, not a teacher.
The provided text boxes are very small, making it impossible to read the entire text and view the applet at the same time. Given the wonderfull job the programmers did putting together these applets,
this is definately negligable, yet an annoying feature of this site. On the other hand I must comment that the translation from French to English was done quite well, with the exception of a few typos
14 years ago
A collection of applets covering many topics in modern physics. Almost all of them were very good.