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I have developed an idea to explain quantum entanglement to a layperson. I would like to discuss it over here and question about issues with it.

Suppose if person A has a box with a robotic hand holding a pen above two blank papers. The two blank papers are separated by a carbon copy paper which imprints whatever is drawn on the first onto another.

Now, the robotic hand randomly draws a straight arrow on one of the paper. It gets copied on the other paper below it. However, the person holding the box has no idea in which direction the arrow points as the box is closed.

Now, somehow we are able to spatially separate one of the papers without Person A knowing anything about the drawn arrow on it. It is given to Person B let's say in another city.

Now, both A and B open their boxes to reveal the direction in which the arrows were drawn and are surprised to find both of their arrows point in the same direction on the paper.

Is this a nice way to explain entanglement? Are there any flaws, misconceptions or warning which need to be addressed before mentioning this analogy? Is initial spatial proximity a necessity for quantum entanglement?

Ruslan
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Chetan Waghela
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1 Answers1

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A crucial element is lacking in your narrative.

That missing element is superposition of states.

About the concept of superposition:
In classical mechanics there it is recognized that sound propagation supports superposition of multiple wavelengths. Example: let's say we create two beams of sound, produced in such a way that the two beams cross each other. Let one beam be a sinus wave of, say, 500 Hz, and the other beam a sinus wave of 550 Hz. A microphone placed at a point where both sound beams are present will not only pick up the separate sounds, but the difference between the two frequencies will also manifest itself as a sound, one of 50 Hz. The point I want to make is this: the two beams do not affect each other. The two sounds propagating in the air are truly independent. That is the concept of superposition.

In the case of entanglement:
If you have, say, two photons, propagating away (in opposite directions) from the point where they were generated: If those photons are in a superposition state the experimentor is in a position to demonstrate/verify the entanglement by performing a measurement of the state. For a sufficiently large number of photon pairs (all generated and measured in sequence) a particular correlation of the measurement results demonstrates/verifies entanglement of the photon pairs.

About superposition state:
Sure: when a photon is in a superposition state you don't know what state is it in.

The point is: the photon doesn't know either. It's not that in some hidden way the photon does already know, and it's only you who doesn't know. The state of the photon is a true superposition state. Only a measurement will make the state unambiguous.

The measurement proces reports a particular state. As with any measurement of a quantum entity that is in a superposition state; which state ends up as the measured state is random.


In a demonstration/verification of entanglement the superposition state is used as a tool. Both photons are subjected to measurment. If the photons are entangled the result of the measurements will show a correlation.


So:
In your attempt at exposition of entanglement to a layperson a crucial element is missing

Cleonis
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