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PROFESSOR: Superposition is very unusual and very interesting. Now we've said about superposition that in classical physics, when we talk about superposition we have electric fields, and you add the electric fields, and the total electric field is the sum of electric fields, and it's an electric field. And there's nothing strange about it. The nature of superposition in quantum mechanics is very strange. So nature of superposition-- I will illustrate it in a couple of different ways. One way is with a device that we will get accustomed to. It it's called the Mach-Zehnder interferometer, which is a device with a beam splitter in here. You send in a beam of light-- input- beam splitter and then the light-- indeed half of it gets reflected, half of it gets transmitted. Then you put the mirror here-- mirror 1, you put the mirror 2 here, and this gets recombined into another beam splitter. And then if there would be just a light going in, here there would be tw...

It's not unusual to find that an application is organized as multiple communicating processes. What's the advantage of using multiple processes instead of just a single process? Many applications exhibit concurrency, i.e., some of the required computations can be performed in parallel. For example, video compression algorithms represent each video frame as an array of 8-pixel by 8-pixel macroblocks. Each macroblock is individually compressed by converting the 64 intensity and color values from the spatial domain to the frequency domain and then quantizing and Huffman encoding the frequency coefficients. If you're using a multi-core processor to do the compression, you can perform the macroblock compressions concurrently. Applications like video games are naturally divided into the "front-end" user interface and "back-end" simulation and rendering engines. Inputs from the user arrive asynchronously with respect to the simulation and it's...