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Dear Dr. B: What is the difference between entanglement and superposition?

2 Mar 2016, 17:15 UTC
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The only photo in existencethat shows me in high heels.This is an excellent question which you didn’t ask. I’ll answer it anyway because confusing entangled states with superpositions is a very common mistake. And an unfortunate one: without knowing the difference between entanglement and superposition the most interesting phenomena of quantum mechanics remain impossible to understand – so listen closely, or you’ll forever remain stuck in the 19th century.Let us start by decoding the word “superposition.” Physicists work with equations, the solutions of which describe the system they are interested in. That might be, for example, an electromagnetic wave going through a double slit. If you manage to solve the equations for that system, you can then calculate what you will observe on the screen. A “superposition” is simply a sum of two solutions, possibly with constant factors in front of the terms. Now, some equations, like those of quantum mechanics, have the nice property that the sum of two solutions is also a solution, where each solution corresponds to a different setup of your experiment. But that superpositions of solutions are also solutions has nothing to do with quantum mechanics specifically. You can also, for example, superpose electromagnetic waves ...