How does one detect a single photon? I understand the double slit experiment up until the point that we begin "detecting" single photons. What does it mean to detect. You cant place a camera in the slit because that would capture the photon just like the photosensitive plates would.
I've also heard that you can do the double slit experiment with electrons. Perhaps you can use the attribute of charge to detect the electron from a distance.
I have read many times of how the double slit experiment works, but never the specific details of how the experimenters manage to shoot single particles and then detect them moving through the slit. Any links describing the equipment used in these experiments would be appreciated
 A: As strange as it may be to hear, the double-slit experiment conducted one photon at-a-time with "detectors at the slits" is nothing short of a myth. No such experiment has been reported in a peer-reviewed journal or any reputable book or publication. Talk of this supposed experiment, and even figures illustrating it, can be found throughout the internet, but these refer to no actual experiment being performed. 
The origin of the myth is a poor popularization of the quantum eraser experiment, which though "marking" the photons traveling through each of the two slits with which-way information and destroying the interference pattern, involves no detectors or recorders in front of or behind the slits except for the main CCD backplate.
A: Any measurement you make at the slits is going to destroy the interference pattern. The wavefunction of the photon or electron collapses as soon at it interacts with the environment in a thermodynamically irreversible way. In essence, any type of measurement you could make that would tell you which slit a particle went through would cause the wave function to collapse and the interference pattern would disappear. In order for the interference pattern to exist on the screen, the particles have to remain in a state of superposition all the way to the screen.
The interference pattern exists even when measuring single photons, which is significant because it shows that the effect is quantum in nature and not explained by any classical statistical interference. The wavefunction of a single particle can interfere with itself. 
One way of measuring single photons is to use a photomultiplier tube. Photons incident on the tube create an avalanche of electrons in each stage that can be detected as a current pulse. Photomultiplier tubes have sufficiently high gain to detect a single incident photon. However, they do not detect every incident photon since their quantum efficiency is less than 100%. There are probably other ways of detecting single photons but this is just one example.
A: The photons are not detected at the slits. They are detected at a distance from the slits as illustrated here: 


Photons or particles of matter (like an electron) produce a wave pattern when two slits are used

This has been done with single photons, as seen in this video.(after 2' it shows single photon interference), and this publication.. The detector of single photons in the video is a photomultiplier at the screen position.
Generally if a detector is put in one slit, the interference disappears. Here is the build up of single electron interference   


Successively longer integration times as electron arrivals (white dots) are recorded.

There have been experiments exploring why when the slit the electron went through is known the interference pattern is destroyed. A recent one  used the following method for detecting which slit the electron passed through:

they modified one of the slits by covering it with a filter made of several layers of “low atomic number” material to create a which-way detector for the electrons passing through. 

They concluded  that the method of detection changes the conditions to the point of destroying interference effects:

Overall, the results suggest that the type of scattering an electron undergoes determines the mark it leaves on the back wall, and that a detector at one of the slits can change the type of scattering. The physicists concluded that, while elastically scattered electrons can cause an interference pattern, the inelastically scattered electrons do not contribute to the interference process.

A: You can't detect single photons. There is no way to prove that a click in a photodetector represents a single photon versus the response of the system to an electromagnetic wave. There is no way to prove that the appearance of a fleck of silver on a photographic plate represents a single photon versus the response of the silver bromide crystal to an electromagnetic wave. See my blogpost on Quantum Siphoning for an explanation.
And while we're on the topic, you can't create single photons at will either. If you could, you would just shoot photons at a photodetector one by one and count them at will. Never been done. Why not? because there are no pea-shotters for photons (see my blogpost).
