HOW can entanglement be observed experimentally?

[dpa]

hi all

i have two questions.
1. Quantum entanglement is observed experimentally. But how can that be. Does not Quantum decoherence effect it from being observed?

2.The general notion is that M String theory if proven is theory of everything. But without explaining entanglement how does it become TOE.

 

[Zarqon]

hi all

i have two questions.
1. Quantum entanglement is observed experimentally. But how can that be. Does not Quantum decoherence effect it from being observed?

Entanglement is typically detected through the measurement of correlations between the entangled particles. They need to display the appropriate non-local correlations to be considered entangled. Decoherence can indeed destroy these features, but decoherence only sets in at a particular time scale, which is given by how strong the coupling to the surrounding environment is, how much the surroundings fluctuate, and also how big your object is. This gives a time scale on which decoherence effects sets in, but as long as you are able to read out all necessary data before that time, you are fine.

 

[Mr_Physicist]

Entanglement is typically detected through the measurement of correlations between the entangled particles. They need to display the appropriate non-local correlations to be considered entangled. Decoherence can indeed destroy these features, but decoherence only sets in at a particular time scale, which is given by how strong the coupling to the surrounding environment is, how much the surroundings fluctuate, and also how big your object is. This gives a time scale on which decoherence effects sets in, but as long as you are able to read out all necessary data before that time, you are fine.

I second Zarqon's explanation. I would also like to point out that while decoherence is a major problem in many experiments in quantum mechanics (such as those involving electrons or ion traps), its is not nearly such an issue in quantum optics. Entangled photon pairs have very few problems with decoherence, one of the reasons that they are attractive for quantum computing (although they possesses other disadvantages). As I recall, Zeilinger et. al. have done experiments where they separate two entangled photons and then send one several miles away where it is collected via telescope and the correlations between them survive. The specifics of what measurements are done to verify entanglement depends on the particular experiment, but it can certainly be done.