Does Observing an Entangled Particle Affect Its Superposition?

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Discussion Overview

The discussion revolves around the concept of superposition and entanglement in quantum mechanics, specifically questioning whether an observed particle can return to a state of superposition after being observed. The scope includes theoretical considerations and conceptual clarifications related to quantum states and measurement.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that if a particle is not observed, it exists in a superposition of states, but once observed, it may not return to that superposition.
  • Others argue that measurement is not reversible, and once superposition is destroyed by observation, stopping observation will not restore it.
  • A participant questions the understanding of terms like "virtual particles," "superposition," and "entanglement," suggesting a need for clearer definitions.
  • Another participant mentions that if a particle's angular momentum is measured, it may be in a superposition of states along a different axis, indicating the complexity of quantum states.
  • Some participants highlight that virtual particles cannot be contained in boxes, challenging the initial scenario posed in the discussion.
  • There is a suggestion that a better approach to discussing superposition would involve preparing a single particle in a known state rather than relying on entangled pairs.
  • One participant emphasizes that observation is an interaction and not a continuous process, further complicating the notion of returning to superposition.

Areas of Agreement / Disagreement

Participants express differing views on the nature of measurement and superposition, with no consensus reached on whether an observed particle can return to a state of superposition after being observed.

Contextual Notes

Limitations include the ambiguity in the definitions of terms used, the nature of virtual particles, and the complexities surrounding the measurement process in quantum mechanics.

Allen_Wolf
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Consider two virtual entangled particles (+ve & -ve particles) which emerged out of nothing.
We keep +ve and -ve in two different boxes. If the box containing +ve particle is closed and we do not observe the particle, then it is said to be in a superposition of +ve and -ve, Right? After some time, we open the box and observe the particle. We then again keep the particle back in the box and close it i.e. stop observing it. Will it again be back into a state of superposition of +ve and -ve?
 
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Allen_Wolf said:
Consider two virtual entangled particles (+ve & -ve particles) which emerged out of nothing.

There is no such thing, so it's hard to consider it.
 
Simply, can an already observed particle return to superposition when we stop observing it?
 
Allen_Wolf said:
Simply, can an already observed particle return to superposition when we stop observing it?

It doesn't need to "return" to it. Whatever its state after the observation, it will be a superposition in some base.
 
Allen_Wolf said:
Simply, can an already observed particle return to superposition when we stop observing it?
You seem to be confusing entanglement and superposition. Do you understand what these terms mean?
 
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Allen_Wolf said:
Consider two virtual entangled particles (+ve & -ve particles) which emerged out of nothing.
We keep +ve and -ve in two different boxes. If the box containing +ve particle is closed and we do not observe the particle, then it is said to be in a superposition of +ve and -ve, Right? After some time, we open the box and observe the particle. We then again keep the particle back in the box and close it i.e. stop observing it. Will it again be back into a state of superposition of +ve and -ve?
Measurement is not reversible. Once the superposition is destroyed by measurement, stopping observation will not restore the superposition.
 
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PeroK is right. It seems like you don't understand what a lot of the terms mean: at least virtual, superposition, entanglement. It might make more sense for you to re-pose your question, carefully checking to see that the words you use are the words you mean.

To answer the question you asked - which I suspect is not the question you intended to ask - if I measure a partcle's angular momentum along the z-direction, it's in a superposition of states along the x-direction.
 
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Allen_Wolf said:
Consider two virtual entangled particles (+ve & -ve particles) which emerged out of nothing.
We keep +ve and -ve in two different boxes.

You can't keep virtual particles in boxes.
 
Allen_Wolf said:
Consider two virtual entangled particles (+ve & -ve particles) which emerged out of nothing.
We keep +ve and -ve in two different boxes. If the box containing +ve particle is closed and we do not observe the particle, then it is said to be in a superposition of +ve and -ve, Right? After some time, we open the box and observe the particle. We then again keep the particle back in the box and close it i.e. stop observing it. Will it again be back into a state of superposition of +ve and -ve?
If you prepare a particle as a member of an entangled pair you cannot ascribe a state to it at all, you have to specify the other particle and talk about the state of the two together. Of course if you cleanly ignore the other particle you can talk about the one you still have but then it is simply a probability distribution - it might be +ve or it might be -ve.

I can see what you are trying to do. You want to specify a scenario where the particle is unambiguously in superposition. Far better to prepare your superposition by taking a single particle, putting it into a known state and then, if necessary, forcing it into a superposition of the two states you want. Doing this with charge is next to impossible, but with spin or polarisation it is quite easy.

Also, quantum states are nothing to do with opening boxes - Schroedinger's cat has a lot to answer for!

And observation isn't a continuous process that we start and stop. It's an interaction.

So let's re-cast your question:
Consider a particle in superposition. After some time, we observe the particle. After observation (assuming it is kept safe from other interactions) will it be back in superposition?
No, it will remain in the state you observed it to be in. That's kind of what observation means.
 

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