In a typical double-slit experiment, where interference patterns are observed, the experiment is often performed with a large number of photons or particles being sent through the apparatus one at a time. This is done by using a source that emits photons or particles individually or in a controlled manner.
There are various methods to achieve this:
Dimmed Light Source: One way to achieve the one-photon-at-a-time condition is to use a very dim light source, such as a laser, and attenuate it to such an extent that only a single photon is present in the apparatus at a given time. This can be achieved using neutral density filters or by reducing the intensity of the light source to a level where the probability of more than one photon being present simultaneously is extremely low.
Quantum Dots or Single-Photon Sources: Another approach is to use specialized light sources, such as quantum dots or single-photon sources. These sources emit individual photons one at a time, allowing for precise control over the number of photons entering the double-slit setup.
Electron or Particle Guns: In experiments involving particles like electrons, it is possible to generate a particle gun that emits particles one at a time. This can be achieved using techniques like electron or particle sources that emit particles in a controlled manner, such as through electron guns or particle accelerators.
By ensuring that only one particle or photon is present in the apparatus at any given time, physicists can observe the interference pattern that arises when particles interact with the double-slit setup. Over many repetitions of the experiment, with one particle at a time, the accumulated results reveal the interference pattern characteristic of wave-particle duality.
It's important to note that while the experiment is conducted with single particles, the interference pattern that emerges is a statistical pattern resulting from the probabilistic nature of quantum mechanics. Individual particles are detected at specific locations, but the interference pattern becomes apparent when looking at the distribution of many particle detections.