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Quantum measurement of energy

  1. May 14, 2009 #1
    I would like to know, does anyone know of specific examples of quantum measurement of energy? The reason I am asking is that anything that is observed is ultimately in a position space as opposed to momentum space (for example, it might be specific position of the errow of a measurement device). So, does energy measurement ultimately involve position measurement? If so, how can we get around the uncertainty relations?

    I also have a related question: how is it possible to measure an energy of a single particleanyway? For one thing, its energy is very small, so how can it be suffi cient to cause something classically observed. Also, in light of second quantization, a particle can decay any time.
  2. jcsd
  3. May 14, 2009 #2


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    My avatar is a CCD image of photoelectrons emitted from a material. The vertical axis is energy, the horizontal axis is momentum. It measures the band dispersion of the material in a particular crystal symmetry direction using angle-resolved photoemission technique.

    The energy is measured, using this instrument, using a series of electrostatic "lenses". But this is similar to putting those photoelectrons (or any charge particle) into a dipole magnet and bending the trajectory. By knowing the strength of the field, and the amount that the particle got bent in the field (i.e you look at a screen and the position where the particle hits), you can measure its energy. This is a technique that we often used in electron particle accelerator.

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