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Decoherence by macroscopic interaction

  1. Jul 14, 2010 #1
    From my understanding decoherence occurs whenever a quantum object interacts with a macroscopic sized object. So for instance a measurement involving a photographic plate registering a particle will cause decoherence of the wavefunction, which appears to us as the wavefunction collapsing. However there are other instances where a quantum object interacts with a macroscopic object which doesn't cause decoherence. For instance a half silvered mirror that acts as a beam splitter in various experiments, and also the partition in the double slit experiment where the wavefunction encounters this but doesn't decohere. What is it physically that differentiates these objects from measurement devices such as photon detectors which does cause the wavefunction to appear to collapse?
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  3. Jul 15, 2010 #2


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    Not necessary. Any mechanism that means that a system is "open" (i.e. can interact with the environment) leads to decoherence.
    In e.g. solid state quantum computing the coherence times are limited by the fact that the qubits couple to large ensembles of microscopic systems; e.g. impurities (atoms, molecules etc.) etc. that can exist in one of two energy states and happens to have an energy splitting close to the qubit frequency (they basically "suck" energy from the system).
    Hence, from a practical point of view we are usually limited by interactions with microscopic objects; the interaction with macroscopic objects really only comes into play during an actual measurement.
  4. Jul 15, 2010 #3


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    One of the papers highlighted in the Recent Noteworthy papers thread in the General Physics section is this:


    You'll notice that even ONE interaction with an additional electron is enough to destroy the 1-particle quantum effect. This means that just one electron is enough to provide the coupling to the "environment" needed to recover the classical picture.

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