Quantum decoherence is the process by which a quantum system loses its distinctively quantum properties, such as superposition and entanglement, due to interactions with its environment. It explains why the strange behaviors predicted by quantum mechanics are not commonly observed in our everyday, classical world.
In a purely isolated system, a quantum particle (like an electron or photon) can exist in a superposition—being in multiple states at once. But in reality, no system is ever perfectly isolated. When a quantum system interacts with its surroundings—such as air molecules, light, or even heat—information about its quantum state “leaks” into the environment.
This interaction causes the system to become entangled with the environment, effectively destroying the coherence between its different quantum states. As a result, the system begins to behave more classically, with well-defined outcomes, instead of showing interference patterns or quantum superpositions.
Quantum decoherence:
- Does not involve measurement, but explains why measurement outcomes appear definite,
- Occurs rapidly, especially in large or warm systems, making quantum effects hard to observe at the macroscopic scale,
- Is a key concept in explaining the quantum-to-classical transition,
- Poses challenges for quantum computing, where preserving coherence is crucial for reliable operation.