When Were Anomalous Correlations in Entangled Photons First Observed?

[jed clampett]

For a properly prepared entangled state of photons, we expect 100% correlation between detection events when filtered through aligned polarizers. I’m wondering when this was first observed experimentally.

It’s not what you’d expect for ordinary photons. If two photons are prepared in the same polarization state, and fired at a random polarizer, the results are a little different. If I’ve calculated correctly, there’s a 37.5% chance they both get through, a 37.5% chance neither gets through, and a 25% chance that one or the other gets through - a 75% probability of coincidence detection. I think that gives you a correlation of 50%. It’s definitely not 100%.

So I wonder when these anomalous correlations for the entangled state were first observed? This topic came up tangentially in another discussion so I thought I should start a new thread for it.

 

[DrChinese]

Good question. The 100% correlation is the quantum prediction for Entangled State statistics. This is calculated a bit different than you might expect, although it reduces to cos^2(theta). I will try to lay that out.

The numbers you mention are what is called Product State statistics. Generally this is .25+(cos^2(theta)/2) and ranges from a minimum of 25% to a max of 75%. As you might guess, the Product State statistics are more properly with a Local Realistic interpretation in which the photons (of a pair) have a single identical but unknown polarization. So this is like an extension to the usual classical wave interpretation. Of course, this prediction does not agree with observation.

 

[DrChinese]

For the QM calculation, you may benefit from this which lays it out:

http://arxiv.org/abs/quant-ph/0205171

See (1), (2), (3) although this does not show as clear as I might hope how it reduces to cos^2(theta).