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Can we take a single lone hydrogen atom (proton and electron?) and set it in one place and observe it staying there?

How about just a proton?

A neutron?

How about just an electron?

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  • $\begingroup$ You can "freeze" molecules in place using laser cooling techniques. But you cannot perfectly localise them due to Heisenberg's Uncertainty Principle. $\endgroup$ – Constandinos Damalas Jul 30 '14 at 12:39
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In liquid helium, there is a phonon resonance with temperature around 11 K that has the same energy and momentum as a cold neutron with wavelength around 9 Å. Neutrons with this wavelength (which have a speed of a few hundred meters per second) essentially undergo a "billiard ball collision" with a phonon and stop. Since liquid helium (with boiling point around 4 K) doesn't contain much background of 11 K phonons to scatter the neutrons back up, you can produce quite a population of "stopped" neutrons. They're technically called ultracold neutrons since they don't quite stop: the typical leftover velocity is 5–10 m/s, slower than a good human sprinter.

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At least for spin-$\frac{1}{2}$ particles like protons and electrons this is not possible. A phenomenon called zitterbewegung is responsible for rapid motion of these particles. The frequency of these motions can be as high as $10^{21}$ hertz.

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  • $\begingroup$ @ACuriousMind: Wikipedia: "Zitterbewegung (English: "trembling motion", from German) is a theoretical rapid motion of elementary particles, in particular electrons, that obey the Dirac equation. The existence of such motion was first proposed by Erwin Schrödinger in 1930... Zitterbewegung of a free relativistic particle has never been observed, but the behavior of such a particle has been simulated with a trapped ion..." I was teached about Zitterbewegung too but now it seems that it's not approved. $\endgroup$ – HolgerFiedler Jul 30 '14 at 20:01
  • $\begingroup$ @HolgerFiedler: I didn't write the answer, I just edited in the link since rotiyan did not explain anything about it. I've got no opinion on whether or not Zitterbewegung is a real or purely fictional phenomenon. $\endgroup$ – ACuriousMind Jul 30 '14 at 20:07
  • $\begingroup$ @ACuriousMind: sorry, my failure. $\endgroup$ – HolgerFiedler Jul 30 '14 at 20:17

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