How do you Send a Single Electron Through a Slit?

In reading about particle/wave duality, I've come across many accounts of the "two slit" experiment which involve "sending a single electron" or "sending a single photon" at the two-slit object. Well, what I want to know is, HOW exactly do physicists "shoot a single photon /electron". What I've read makes it sound as if we can load a very small BB gun with a single photon, and fire it. How is this physically done? How do we know we're shooting one, single electron at something?
- Adam Pace (age 47)
Seminole, FL USA

Good question!   First of all you must have a detector that is able to detect a single photon or electron.  A photomultiplier or sensitive CCD detector will do. (I know they work as I have used them in my own research projects.)   Then you have to calibrate the detector with a known flux of light or current of electrons: a standard procedure.   After that you insert the double slit into the beam and start turning down the amount of incident flux by inserting appropriate filters or by reducing the amount of current in the case of electrons. After enough attenuation you can be assured that there are so few incident particles that it is very, very improbable that two of them arrived within the time resolution of the detector.  Nevertheless, the interference pattern persists irrespective of the intensity of the incident beam.

LeeH

(published on 12/28/2009)