Decorrelate 2 particles initially entangled

  • #1
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Main Question or Discussion Point

Hello,

I am studying the entanglement in quantum physics, especially the Aspect's experience where 2 photons initially correlated keep this correlation through the measure of their polarity. The Wikipedia article is only available in French, but there is an article in English written by Alain Aspect ( https://physics.aps.org/articles/v8/123 ) here that describes the experiments.

I am wondering if there is a way, from an experimental or theoretical point of view, to decorrelate 2 entangled particles ?

Is there any experience which has be performed in this goal to remove the entanglement ?

On another forum, one told me that Entanglement is destroyed by Quantum decoherence ( https://en.wikipedia.org/wiki/Quantum_decoherence ) and that any interaction with a system that has many degrees of freedom will do it.

If I have well understood, a system of 2 entagled particles can't be never considered as an isolated system, can it ? however, for the moment, we don't know if there is a distance limit for entanglement, beyond which entanglement would have disappeared, is it right ?

If there is a distance limit, then we could consider maybe that Quantum decoherence destroys the entanglement.

thanks for your clarifications
 

Answers and Replies

  • #2
DrChinese
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There is no one hard and fast rule. Entanglement comes in many forms, in fact it comes in many counter-intuitive forms.

Generally, once an entangled particle (say entangled as to spin) interacts irreversibly with a system on its entangled basis, it will no longer be correlated (entangled) with its former partner. It is often possible to interact with such a particle in such a way that it does not cause decoherence on a particular basis.
 
  • #3
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@DrChinese

Thanks for your answer. From your said, it seems that answer to my question is not binary. Do you want to say that, "Generally", a entangled system interacts with its surrounding since the system totally isolated is an ideal case. From experimental point of view, I mean concretelly, 2 polarizing entangled photons will interact with vacuum fluctuations and its virtual photons, won't they ?

So, I should ask rather : in which experimental cases the entanglement is preserved , even considering system as not perfectly isolated ?
 
  • #4
DrChinese
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Any case in which the value of an entangled property is NOT learned, that would be a scenario where entanglement continues. Without discussing the merits of the existence of virtual particles: virtual particles do NOT collapse entanglement.

You can also transform entangled properties without revealing an underlying value. An example of that would be using a wave plate to rotate photon polarization. Or reflecting a photon off a mirror. These interactions with an external apparatus do not cause decoherence.
 
  • #5
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@DrChinese

So what process or physical entities causes decoherence : the environment, i.e the surrounding ... ?

You say that, in the case of reflecting a photon off a mirror, the interactions with an external apparatus don't cuase decoherence : so you suppose that system "photon + mirror" is totally isolated ?

Why virtual particles are not interacting with an entanglement system ? for example, diffusion between entantgled particles and virtual ones can't occur ?

Sorry for my bad english, I try to be clear as can as I do.
 
  • #6
DrChinese
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So what process or physical entities causes decoherence : the environment, i.e the surrounding ... ?

You say that, in the case of reflecting a photon off a mirror, the interactions with an external apparatus don't cuase decoherence : so you suppose that system "photon + mirror" is totally isolated ?

Why virtual particles are not interacting with an entanglement system ? for example, diffusion between entantgled particles and virtual ones can't occur ?
It doesn't work that way. You need not consider the mirror as isolated, nor consider an entangled particle as not interacting with virtual particles.

The issue is that no information is irreversibly gained - whether you know it or not - about particle on the entangled basis. If it is possible (in principle) to obtain that information from the setup, then entanglement will end. With photon interaction with a mirror, for example, it does not take on a specific value of polarization even though the polarization is reversed. The superposition remains, and thus entanglement continues.
 

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