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In Wikipedia it is mentioned that position and momentum can be entangled as well as spin and polarization etc. I assume etc. is charge etc. I understand how if you measure spin up on one of a pair you get spin down on the second of the pair.

What happens to the other particle in an entangled pair if I measure the momentum, position or charge of one of the particles?

Is there a momentum up and down or charge up and down analog?

http://en.wikipedia.org/wiki/Quantum_entanglement

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1 Answer 1

Momentum conservation holds also for quantum mechanics. Energy and momentum conservation are used in studying elementary particle interactions continuously.

In a two body reaction the momenta are correlated, but unknown before measurement. After measuring the momentum of one of the particles, if the masses are known, one knows the momentum of the one that was not measured/observed using momentum conservation.

A prime example was the discovery of the neutrino, which was discovered by imposing energy and momentum conservation on the reaction. Within the accuracies of the experiments the neutrino mass was of order zero, though later, neutrino oscillations showed that neutrinos have a small mass, currently given by upper limits.

By the way, "entanglement" is a fancy way of talking of correlations, and is misleading, since there is nothing mysterious about conserving momentum energy and quantum numbers.

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Does that mean it's not the same type of entanglement? –  Jitter Nov 12 '13 at 6:36
    
Just to be specific, if I have an entangled electron pair and I measure the momentum of one electron will it always be equal to the other electron or can it vary? –  Jitter Nov 12 '13 at 6:53
    
It must conserve momentum Input total momentum - measured of one electron will always give the momentum of the unmeasured one. –  anna v Nov 12 '13 at 7:20
    
"Does that mean it's not the same type of entanglement" It is exactly the same type, in momentum the values are continuous, for spins they are discrete. –  anna v Nov 12 '13 at 7:21
    
Thankyou anna, looks like I can't tell what mesurement was made on my other qubit at a distance;-) –  Jitter Nov 12 '13 at 8:11

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