Coherence refers to the property of a system or a wave where the phases of different components or parts are correlated or aligned with each other. In the context of quantum mechanics, coherence is closely related to the wave-like behavior of particles and the interference phenomena observed in experiments.
When we talk about coherence in a quantum system, such as an electron or a photon, it means that the wave functions associated with different parts of the system are in phase or correlated. This coherence allows for the interference of the wave functions, resulting in observable interference patterns.
In the context of a double-slit experiment, for example, coherence is essential for the formation of the interference pattern on the screen. When the two slits are illuminated by a coherent light source, such as a laser, the wave functions associated with the two slits are in phase with each other. As a result, they interfere constructively or destructively, leading to the observed pattern of bright and dark fringes on the screen.
However, when the coherence is lost or disrupted, such as through interactions with the environment, decoherence occurs. Decoherence causes the phases of the wave functions associated with different parts of the system to become uncorrelated or out of phase, destroying the interference pattern and leading to a classical-like behavior.
In summary, coherence refers to the alignment or correlation of phases in a wave, and it is crucial for observing interference phenomena. When coherence is present, the wave functions associated with different parts of the system can interfere with each other, resulting in observable interference patterns. Decoherence, on the other hand, disrupts the coherence and leads to the loss of interference.