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Recently started to learn how the confinement in quantum dots affects the momentum and position of the electron wave as the dot gets smaller. As possible positions of the wave become smaller, the uncertainty of the momentum becomes bigger.

Yet, the increase in momentum seems like it would violate conservation of energy to me.

Imagine the following thought experiment. There is an electron looping around an electric field at constant velocity. As it moves, it will release cyclotron radiation corresponding to its mass and velocity.

Now say we envelop it in a spherical donut that keeps progressively shrinking. As its position becomes more known, its momentum will change, being either a big numerical answer or smaller. Simultaneously, as it has a constant velocity; the only way for its momentum to change is by an increase in mass, i.e its velocity should not be relativistic.

As it revolves and its mass oscillates, it will release very high energy/frequency radiation when its momentum becomes high and low frequency/energy radiation when the mass is low. Wouldn’t this be breaking conservation of energy? It would taking energy out of apparent nothingness when as it emits higher energy that when it has lower mass at a random moment in time.

Unless my thought experiment or my conceptual understanding is erroneous, how would this not break conservation of energy?

  • "There is an electron looping around an electric field at constant velocity." Constant speed is not constant velocity. if it is looping it it will radiate due to the loop – anna v Oct 06 '22 at 04:10
  • Your are correct. It will be radiating like in a cyclotron. I’m sure I stated that. Why is the question closed? – Evamentality Oct 07 '22 at 00:15
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    Your assumption that electrons behave like classical objects is simply false. A charged quantum dot has energy levels and bands that can be excited with light and then it will give off light of a different frequency. That's no different from an atom. – FlatterMann Oct 07 '22 at 00:18
  • Right, but I’m not talking about a quantum dot. In any case, when shrinking the doughnut around the electron as it is looping around the electric field, are you saying that it will stop moving and just get confined? – Evamentality Oct 07 '22 at 01:00
  • @Evamentality you seem not to understand that radiation takes away energy and momentum so there is no conservation. In addition the electron mass is constant, it is the invariant mass that enters the calculations – anna v Oct 07 '22 at 03:29
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    As @Flatterman notes, a quantum dot is an artificial atom, and your thought experiment of an "electron looping around an electric field" sounds like a classical (as opposed to quantum) atomic model of an electron orbiting a nucleus. As you have discovered, such models don't work. I suggest looking at the answers to the related question "Why don't electrons crash into the nuclei they "orbit"?". – David Bailey Oct 07 '22 at 05:49

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