In a two-slit experiment with electrons, if we place detectors near each slit to try to detect the presence of the electron without directly observing its path, the experiment's outcome will be different from the traditional double-slit interference pattern.
The interference pattern arises when electrons or other particles exhibit wave-like behavior and interfere with themselves as they pass through the two slits. This interference pattern is a result of the superposition of different possible paths the electron can take. When the electron's wavefunction encounters both slits, it splits and then recombines, leading to regions of constructive and destructive interference on the screen where the electrons are detected.
However, if we introduce detectors near each slit to determine which slit the electron passes through, we disrupt the interference pattern. This is known as the "which-way" or "which-path" measurement. The act of detecting which slit the electron goes through introduces an interaction between the electron and the detector, which collapses the electron's wavefunction into a well-defined path rather than a superposition of paths.
The introduction of the detectors destroys the interference because the electron is forced to behave more like a classical particle with a definite trajectory. The electron's wavefunction is no longer spread out to produce an interference pattern, and instead, we observe two distinct distributions of electrons corresponding to each slit. The result is a pattern similar to what we would expect if we were just firing particles through two separate slits.
It's important to note that the act of measurement or detection itself plays a significant role in the outcome of the experiment. In the presence of the detectors, the wave-particle duality of the electron is disrupted, and we no longer see the characteristic interference pattern associated with quantum behavior.