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I could never understand the part of quantum where only two particles could be entangled at a time with each other and multiple particles couldn't be entangled

by snissn 7y ago

I could never understand the part of quantum where only two particles could be entangled at a time with each other and multiple particles couldn't be entangled together.

hnews_account_1 7y ago
Multiple particle entanglement is the common state. 2 particle entanglement is a special state achieved for research and manipulative purposes. A quantum computer is made up with multiple particles being entangled. If they didn't, the speedup would only be a parallelised version of a 4x speed normal computation.
- PaulHoule 7y ago
  Actually quantum entanglement is the reason why solids are solid (fermi statistics) and why lasers are coherent (bose statistics.) The point of quantum entanglement is that it is not right to plot the wavefunctions for separate electrons (e.g. quarks, photons, ...) but rather you have a wavefunction for all of the electrons at once -- for N electrons the arguments of the wavefunction could be the positions of the N particles (or the momentum) It's that way all the time, whether people are doing an experiment to demonstrate entanglement or not. The "solid matter" and "laser" effects happen because of the two possible symmetries when you swap two of the particles -- either the wave function stays the same when you swap two particles (photons) or it goes 180 out of phase (electrons)
  - hnews_account_1 7y ago
    I don't know if EM phase coherence is a question of quantum entanglement. I think it can be achieved regardless of it i.e. if a laser was made of unentangled photons that just happened to be in phase, it'd still function as a laser. Imagine if all the photons in a laser are entangled: it'd mean any partial interference with the laser would interfere with the whole wave .. which, correct me if I'm wrong, but I don't think that happens. Like not all lasers are bose einstein condensates, though lasers can be made from the emissions of such a state. I could be entirely wrong about this. It's been a while since I went back to quantum physics.
    - PaulHoule 7y ago
      See https://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_statistics https://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_statisti... "The aggregation of particles in the same state, which is a characteristic of particles obeying Bose–Einstein statistics, accounts for the cohesive streaming of laser light" Fermi statistics mean that you can't put two electrons in the same state, but photons want to dogpile into the same state, that's what stimulated emission is all about.
sp332 7y ago
Multiple particles can be entangled. But it opens the system up to even more outside noise, so they tend to fall apart faster.

by snissn 7y ago

I could never understand the part of quantum where only two particles could be entangled at a time with each other and multiple particles couldn't be entangled together.

hnews_account_1 7y ago

Multiple particle entanglement is the common state. 2 particle entanglement is a special state achieved for research and manipulative purposes. A quantum computer is made up with multiple particles being entangled. If they didn't, the speedup would only be a parallelised version of a 4x speed normal computation.

PaulHoule 7y ago
Actually quantum entanglement is the reason why solids are solid (fermi statistics) and why lasers are coherent (bose statistics.) The point of quantum entanglement is that it is not right to plot the wavefunctions for separate electrons (e.g. quarks, photons, ...) but rather you have a wavefunction for all of the electrons at once -- for N electrons the arguments of the wavefunction could be the positions of the N particles (or the momentum) It's that way all the time, whether people are doing an experiment to demonstrate entanglement or not. The "solid matter" and "laser" effects happen because of the two possible symmetries when you swap two of the particles -- either the wave function stays the same when you swap two particles (photons) or it goes 180 out of phase (electrons)
- hnews_account_1 7y ago
  I don't know if EM phase coherence is a question of quantum entanglement. I think it can be achieved regardless of it i.e. if a laser was made of unentangled photons that just happened to be in phase, it'd still function as a laser. Imagine if all the photons in a laser are entangled: it'd mean any partial interference with the laser would interfere with the whole wave .. which, correct me if I'm wrong, but I don't think that happens. Like not all lasers are bose einstein condensates, though lasers can be made from the emissions of such a state. I could be entirely wrong about this. It's been a while since I went back to quantum physics.
  - PaulHoule 7y ago
    See https://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_statistics https://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_statisti... "The aggregation of particles in the same state, which is a characteristic of particles obeying Bose–Einstein statistics, accounts for the cohesive streaming of laser light" Fermi statistics mean that you can't put two electrons in the same state, but photons want to dogpile into the same state, that's what stimulated emission is all about.

sp332 7y ago

Multiple particles can be entangled. But it opens the system up to even more outside noise, so they tend to fall apart faster.