# Entanglement $g^{(2)}$ experiment - what components do I need?

Physics Asked by photongirl on July 23, 2020

I would like to measure whether my source emits entangled photon pairs. To that order I want to build a $$g^{(2)}$$ experiment, which measures photon coincidence counts as a function of time delay between photon detection.

Unfortunately, there is no one here who can show me how. Are there any books or papers that specify what components I need and why? I imagine that it must be much more complicated than hooking up two detectors to my source via fiber optics, right?

Also any hints at how to approach such a setup would be much appreciated. (I’m a first year grad student with next to no supervision.)

Wow, I am impressed by your ambition. Well, the usual way in which people test to see if a source is entangled is to perform a Bell test. In the link you'll find a list of groups that have done work on this. The basic idea is to perform simultaneous measurements of two photons after having performed some projections on them and then combine the results to see if they violate some inequality.

If you want to do more than just see whether the source is entangled, by making a measurement of state as a whole, you may want to do quantum state tomography. There are different ways, depending on what you are looking for.

These experiments are not simple to perform. Hope you won't become discourage if you don't succeed at first.

Answered by flippiefanus on July 23, 2020

A scheme to measure correlation functions via homodyne detection can be found in https://arxiv.org/abs/quant-ph/0602124 I find https://arxiv.org/abs/quant-ph/0506029 easier to understand. Hope it helps somehow.

Answered by Karl Pilkington on July 23, 2020

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