Decoherence and measurement are related concepts in quantum physics, but they are not synonymous.
Decoherence refers to the process by which a quantum system interacts with its environment, causing the system to lose its quantum coherence and behave more classically. When a quantum system becomes entangled with its surrounding environment, the superposition of quantum states can be disrupted, leading to a loss of interference effects and the appearance of classical behavior. Decoherence is a major challenge in quantum systems because it limits the ability to maintain and manipulate delicate quantum states.
Measurement, on the other hand, is a specific type of interaction between a quantum system and an observer or a measurement apparatus. When a measurement is performed on a quantum system, it effectively "collapses" the system's wavefunction into one of its possible measurement outcomes. This collapse is often described using the Copenhagen interpretation of quantum mechanics. Measurement involves extracting classical information from the quantum system, and it can lead to the loss of information about the system's initial quantum state.
While measurement is one possible cause of decoherence, not all interactions that lead to decoherence are measurements. Decoherence can arise from a variety of environmental interactions, such as scattering of photons, interactions with surrounding particles, or thermal effects. These interactions can introduce random phase shifts and entangle the quantum system with its environment, effectively causing the loss of coherence.
In summary, decoherence refers to the process by which a quantum system loses its quantum coherence due to interactions with the environment, while measurement is a specific type of interaction that collapses the quantum state into a specific outcome. Measurement can contribute to decoherence, but decoherence can occur even in the absence of measurement due to interactions with the environment.