In the double-slit experiment, when using a light source that emits photons, it is important to ensure that the light source emits photons one at a time to observe the interference pattern properly. This can be achieved using a specific type of light source known as a "single-photon source."
A single-photon source is designed to emit individual photons rather than a continuous stream of photons. There are several techniques to generate single photons, such as using certain types of quantum emitters or manipulating the properties of light to create photon pairs and then detecting only one of the pair.
Once a single-photon source is used, the emitted photons are directed towards the double-slit apparatus. Due to the nature of quantum mechanics, the single photon does not pass through both slits simultaneously but instead undergoes a wave-like superposition of possible paths.
After passing through the slits, the photon's wave-like nature leads to interference between the two possible paths it can take. This interference results in an interference pattern on a screen or detector placed behind the slits. Over time and with repeated experiments, the accumulation of many single photons forms the observable interference pattern.
The key point to note is that even though individual photons are sent through the slits one at a time, their wave-like nature allows for interference effects to occur. This phenomenon highlights the probabilistic nature of quantum mechanics, where each individual photon interacts with the slits and produces a pattern that contributes to the overall interference pattern over multiple trials.
By carefully controlling the experimental setup and ensuring that only one photon is present at a time, scientists can study the interference pattern generated by single photons, providing insights into the wave-particle duality and the fundamental nature of quantum systems.