3 ms·

> One half of the pair was then observed, and the time for the other half to assume the same state is measured. How?? How is it possible to observe whether or

> One half of the pair was then observed, and the time for the other half to assume the same state is measured. How?? How is it possible to observe whether or not an entangled particle has had its state resolved by the other particle being observed?

sbashyal 14y ago
In a pair of quantum particles [1], when one is spinning-up, other is spinning down even when they are separated. Therefore it is possible to find out about the state of one by looking at the other. [1] http://en.wikipedia.org/wiki/Quantum_entanglement#Concept http://en.wikipedia.org/wiki/Quantum_entanglement#Concept
- colanderman 14y ago
  Yes but doing so collapses the wavefunction. Hence there's no way to observe when the wavefunction collapses.
  - ubercow13 14y ago
    By a series of repeated experiments and statistical inference?
  - aroberge 14y ago
    Many (most?) interpretations of quantum mechanics do not involve a "collapse" of the wavefunction. The Copenhagen interpretation, which is the oldest and better known, does, but the many-worlds interpretation (which I dislike), which is favoured by many working in cosmology and quantum gravity, does not involve a collapse of the wavefunction.
lnanek2 14y ago
Well, for entangled light, figuring out the path taken by one part of the pair forces both to produce no interference patterns. Their superpositions both collapse into a set state. I assume there's a similar effect for electron deflection or whatever they are using. Electron beams can similarly produce interference patterns.
- pdonis 14y ago
  They're using photons, not electrons, but they're not using any interference patterns for detection since they're not bringing the entangled photons back together. They are detected separately.
pdonis 14y ago
How is it possible to observe whether or not an entangled particle has had its state resolved by the other particle being observed? It isn't. All they can detect immediately (i.e., when each photon is detected) is the measured polarization of each individual photon. They can't know the correlation between the two, which is what tests the entanglement, until the results from both measurements are brought together, which happens slower than light.

sbashyal 14y ago

In a pair of quantum particles [1], when one is spinning-up, other is spinning down even when they are separated. Therefore it is possible to find out about the state of one by looking at the other. [1] http://en.wikipedia.org/wiki/Quantum_entanglement#Concept http://en.wikipedia.org/wiki/Quantum_entanglement#Concept

colanderman 14y ago
Yes but doing so collapses the wavefunction. Hence there's no way to observe when the wavefunction collapses.
- ubercow13 14y ago
  By a series of repeated experiments and statistical inference?
- aroberge 14y ago
  Many (most?) interpretations of quantum mechanics do not involve a "collapse" of the wavefunction. The Copenhagen interpretation, which is the oldest and better known, does, but the many-worlds interpretation (which I dislike), which is favoured by many working in cosmology and quantum gravity, does not involve a collapse of the wavefunction.

lnanek2 14y ago

Well, for entangled light, figuring out the path taken by one part of the pair forces both to produce no interference patterns. Their superpositions both collapse into a set state. I assume there's a similar effect for electron deflection or whatever they are using. Electron beams can similarly produce interference patterns.

pdonis 14y ago
They're using photons, not electrons, but they're not using any interference patterns for detection since they're not bringing the entangled photons back together. They are detected separately.

pdonis 14y ago

How is it possible to observe whether or not an entangled particle has had its state resolved by the other particle being observed? It isn't. All they can detect immediately (i.e., when each photon is detected) is the measured polarization of each individual photon. They can't know the correlation between the two, which is what tests the entanglement, until the results from both measurements are brought together, which happens slower than light.