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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.)

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    $\begingroup$ Of course I have been to the library and conducted Internet research. :) I just wasn't successful and was hoping someone could point me in the right direction. Are there any books at all that talk about how to set up such experiments or am I supposed to learn from knowledgable colleagues (that I don't have)? How does this work? So far papers seem to be more about the results than about the methods. $\endgroup$ – photongirl Sep 19 '14 at 18:37
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    $\begingroup$ This is not helpful and I don't like your tone. $\endgroup$ – photongirl Sep 19 '14 at 22:08
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    $\begingroup$ It is true that it's difficult to find descriptions regarding basic experimental setup and tuning in quantum optics papers in general. Papers that describe their setups for doing more advanced experiments never go through the detailed steps required for alignment or where/how to purchase the right stuff. It is of course implicitly assumed that whoever is reading those things work in the field and know the basics :) I do think it might be easiest to discuss in person with someone at a local physics lab. $\endgroup$ – BjornW Sep 20 '14 at 9:50
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    $\begingroup$ Many papers do make it sound like it's a relatively straightforward measurement (see e.g. this example) but conclusive $g^{(2)}(0)<1$ measurements are still hard even in the best-equipped labs around. (I have heard from O'Brien that every Mandel dip observation is considered a significant triumph, often requiring several months of effort.) The reason is that 'indistinguishable' really means indistinguishable in every way, including perfect spatial and temporal mode matching, and that's never a trivial pursuit. $\endgroup$ – Emilio Pisanty Nov 9 '15 at 13:06
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    $\begingroup$ I don't know whether the problem is still pending, but you could search the literature for Hanbury Brown and Twiss setups and experiments. $\endgroup$ – jkalden Feb 21 '17 at 12:59
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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.

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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.

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  • $\begingroup$ General comment/advice: It is better (and appreciated here) to link to the abstract page rather than the PDF. It loads faster (even more so on the phone etc.), and in some cases people just want to know what reference it is, rather than actually look into it. $\endgroup$ – Norbert Schuch Jul 22 at 18:48

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