What is quantum entanglement?

Quantum entanglement is a fundamental phenomenon in quantum mechanics where two or more particles become interconnected in such a way that the state of one particle cannot be described independently of the state of the other(s), even when the particles are separated by large distances. This means that the measurement of one particle's properties (like its spin, polarization, or position) instantly correlates with the measurement of the other particle's properties, regardless of the distance between them. Key characteristics of quantum entanglement include: 1. **Non-locality**: Changes to one entangled particle seem to affect the other instantaneously, regardless of the distance separating them. This has been famously described as "spooky action at a distance" by Albert Einstein. 2. **Superposition**: Before measurement, entangled particles exist in a superposition of all possible states. When one particle is measured, it collapses the superposition and determines the state of the other particle. 3. **Bell's Theorem**: Experiments confirming quantum entanglement, such as those based on Bell's inequalities, show that no local hidden variable theory can explain the correlations observed between entangled particles, reinforcing the non-local nature of quantum mechanics. Quantum entanglement has profound implications for our understanding of quantum information theory, quantum computing, and quantum cryptography, enabling concepts like quantum teleportation and superdense coding. It remains a key area of research in fundamental physics and technology development.