Quantum fun: how identical must "identical photons" be?

[n2doc]

By Chris Lee |

I have completely lost count of how many times I have read phrases like, "Consider a light source that emits photon pairs that are indistinguishable." This indistinguishability, along with the ability of these pairs to be correlated, plays a central role in the games that we play with quantum mechanics.

This isn't only a matter of games for academics—there are also security and computational applications that depend on photons that are (theoretically, at least) indistinguishable. But real experiments use real equipment that is never quite ideal. In some ways this is a benefit, because an ideal pair of detectors would detect differences in our slightly-less-than-ideal photons, destroying experiments and generating cynical graduate students.

Now, some new research from ETH Zurich and Aalto University in Finland explores how imperfect indistinguishability alters the appearance of quantum effects.

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http://arstechnica.com/science/news/2010/04/how-identical-do-identical-photons-have-to-be.ars