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Delayed choice quantum eraser

  1. Mar 25, 2013 #1
    How accurate is this statement:

    After the photon passes through the detector, it then passes through the eraser. The eraser is an electronic device that alters the wave-function of the photon, just like the detector is an electronic device that alters the wave-function of the photon.

    This guy is claiming that after the photon goes through the detector it then goes through an eraser and the eraser returns it to an interference pattern.

    This is from Greene's Fabric of the Cosmos
    It seems to me that they are erasing the tagging device above the slits after the photon passes through it, they are not sending a photon through an eraser.
    Last edited: Mar 25, 2013
  2. jcsd
  3. Mar 25, 2013 #2


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    Not very accurate. It is also not close to what Greene is claiming.

    First of all, it is important to note that the 'tagging device' is NOT a detector. It just leaves some mark on the beam using a reversible interaction (like polarization rotation), but does not perform any measurement. The eraser is not necessarily an electronic device. In most cases, it is just a piece of optics. For example, if one used orthogonal linear polarizations for tagging beforehand, a polarizer oriented at 45° to these polarizations will do as it lets both polarizations pass with equal probability and the resulting beam will have the same polarization irrespective of which of the two initial polarizations entered the eraser.
  4. Mar 29, 2013 #3
    I want to get a second opinion on what this guy is saying, the words in bold. A third and fourth opinion would be nice.

    The detector destroys the interference pattern. The eraser restores it.

    Natural laws don't do anything. The detector is made up of charged particles. Charged particles interact with photons. The natural laws that describe how the detector interacts with the photon are the same natural laws that describe how charged particles interact with photons. Specifically, the law in question is quantum electrodynamics.

    Right. We now understand that the wave function of the photon interferes with itself. Specifically, when the photon passes through plate with the two slits, the wave-function of the photon interacts with the plate such that you have two wave fronts coming out, one through each slit. Those two wave fronts interfere with each other.

    Again, quantum electrodynamics describes this. No natural law is causing it, because natural laws do not cause anything to happen. They are descriptions, not causes.

    What causes the interference pattern to be destroyed when a detector is put into the system is the detector itself. The detector interacts with the photon in such a way that the wave function is no longer two wave fronts coming out, one through each slit, but instead a single wave front coming out from just one of the slits.

    And likewise, what causes the interference patter to reappear when the eraser is used is the eraser itself. The eraser interacts with the photon, resulting in two wave fronts that interfere with each other. As a result, the interference pattern reappears.

    All of this is accurately described by quantum electrodynamics, which is part of the standard model.
  5. Mar 30, 2013 #4
    Still hoping for an answer to this.
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