Yes, it is indeed possible to pass a single electron or a single photon through a double-slit experiment. In fact, the double-slit experiment has been performed with various types of particles, including electrons, photons, and even larger molecules like buckyballs.
In such experiments, a source is used to emit particles one at a time, ensuring that only one particle is present in the apparatus at a time. For example, in the case of electrons, an electron gun can be used to emit electrons individually, and similar techniques exist for photons. This ensures that the particles are not influenced by interactions with other particles during their passage through the experiment.
Regarding the detection of individual particles, there are various techniques employed to observe the passage of single electrons or photons. For instance, in the case of electrons, a sensitive detector, such as a phosphorescent screen or a particle detector, can be placed behind the double-slit setup. When an electron passes through one of the slits and interacts with the detection screen, it can be registered as a discrete event or a localized spot. Similarly, for photons, specialized detectors or photographic plates can be used to observe individual photons.
It is important to note that the act of detecting the particle can interfere with the interference pattern that is characteristic of the double-slit experiment. When the detection apparatus is employed, it effectively "collapses" the wavefunction of the particle and reveals its position. This interference between the particle and the measurement apparatus is a fundamental aspect of quantum mechanics, known as the measurement problem.
In summary, it is indeed possible to pass single particles, such as electrons or photons, through a double-slit experiment, and detection techniques exist to observe their passage as discrete events. However, the act of detection can affect the interference pattern, revealing the particle-like behavior of the individual particles rather than their wave-like nature.