Some of the replies, as is prone on physics forums are wrong.
You can apply OAM to a single photon, and we do.
https://en.wikipedia.org/wiki/Orbital_angular_momentum_of_lightThis expression is generally nonvanishing when the wave is not cylindrically symmetric. In particular, in a quantum theory, individual photons may have the following values of the OAM:
Probably run a search "single photon OAM" for a list of various experimental results and tests.
The problem is single photon OAM can't be described in classical physics which is the same answer wikipedia is giving. As I stated I need another dimension to describe it mathematically or by language. The same problem as our collapse of Paul's wavicle you are going to have to make a cute fairytale and I can't think how to do it.
That is why I was wondering if Prof Chris Baird has a way of dealing with this for layman using classical physics.
For the record you can also entangle single photons carrying OAM, classical physics worst nightmare. Which answers your final question about how do we know, if detection destroys the photon. You measure the entangled partner (destroying it) but leaving the original to proceed as normal. The record for photon entanglement is with around 3000 atoms so you can get a number of measurements if you want. Remember destroying an entangled photon does nothing to the original partner you just don't share QM correlations anymore.
Now you should be able to understand how this experiment works. Your entangled photon you measure never sees the target but the entangled partner does so you can see it.
http://news.nationalgeographic.com/news/...photon-science/So in answer to your question, well we are more than a little sure, by experiments. This is that thing that no other framework makes
predictions that are correct. Infact most can't even explain it much less predict anything. Classical physics just stops and says what happens can't
Edit: LOL was seeing what was out there in search land and look different answer on same forum, same citation as me
http://physics.stackexchange.com/questio...-single-photonsHere is a pretty cute use of single photon OAM
http://www.extremetech.com/extreme/15583...uantum-internet
