Entangled particles and measurement

In summary, the conversation discusses the concept of entanglement between particles and how it affects interference patterns. It is noted that measuring an observable on one of the entangled particles causes the interference to disappear, and it is questioned whether it is possible to measure both particles simultaneously to maintain the interference. It is concluded that entangled particles do not show an interference pattern and this is confirmed by the fact that there is always a time difference when measuring the particles. The conversation also touches on the idea that entanglement can explain why interference is lost in the double slit experiment when trying to determine the electron's position. It is mentioned that when particles interact with each other, they can become entangled.
  • #1
JK423
Gold Member
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We know that if, for example, two particles are entangled in a state like: |Ψ>=a |0>|0> + b |1>|1>, then measuring an observable on only one of the particles it makes the interference dissapear.
But isn't it impossible to measure both particles simultaneously in order to maintain the interference?? There should be an infinitsimal time difference!
That leads me to the conclusion that if two particles get entangled then no interferences will ever appear. Would you agree?

Also, the above can explain for example why in the double slit experiment interference is lost when we try to specify the electron`s position (which slit). When the photon scatters from the electron, their interaction makes them somehow get entangled. So, when the electron hit the wall (position measurement) the interference is lost just because it`s entangled to the photon that scattered!
If the scattered photon is detected first (measurement), then its' state collapses and so does the electron`s. That means, no interference again.
Is the above description any close to reality?

And one last question! I mentioned above that in the photon-electron scattering the particles somehow get entangled. In general, when particles interact with each other, they get entangled??
 
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  • #2
JK423 said:
We know that if, for example, two particles are entangled in a state like: |Ψ>=a |0>|0> + b |1>|1>, then measuring an observable on only one of the particles it makes the interference dissapear.
But isn't it impossible to measure both particles simultaneously in order to maintain the interference?? There should be an infinitsimal time difference!
That leads me to the conclusion that if two particles get entangled then no interferences will ever appear. Would you agree?

A couple of points. First, interference disappears for entangled photons if the possibility merely exists to determine which-slit information. It only "returns" (this is a bit too complex to get into in a paragraph) if you erase that possibility. Second, as you suggest, there is a time difference when measuring Alice and Bob pretty much no matter how you set things up.

So essentially, your conclusion is correct. Groups of entangled photons NEVER show an interference pattern directly.
 
  • #3
Thanks a lot DrChinese!
If there are any other comments on the rest of the OP, they`d be welcome!
 

1. What are entangled particles?

Entangled particles are pairs of particles that are connected in a way that their properties are linked together, regardless of the distance between them. This means that if you measure a property of one particle, the other particle will have a corresponding property.

2. How are particles entangled?

Particles can become entangled through a process called quantum entanglement, which occurs when two particles interact or are created at the same time and location. This creates a quantum state where the particles are correlated and their properties are intertwined.

3. What is the significance of entangled particles?

The significance of entangled particles lies in the potential applications in quantum communication and computing. Since the particles are connected, any changes to one particle will result in corresponding changes to the other particle, making them useful for secure communication and information processing.

4. How are entangled particles measured?

Entangled particles are measured by observing their properties, such as spin or polarization. This can be done by using specialized equipment, such as photon detectors, to measure the particles' properties and determine their correlation.

5. Can entangled particles be used for faster-than-light communication?

No, entangled particles cannot be used for faster-than-light communication. While changes to one particle will result in corresponding changes to the other particle, this information cannot be communicated faster than the speed of light. This is due to the principle of causality, which states that no information can travel faster than the speed of light.

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