Entanglement is a fundamental concept in quantum mechanics that describes a strong correlation between two or more particles, even when they are physically separated. It is a phenomenon that occurs when particles become intertwined in such a way that the state of one particle cannot be described independently of the state of the other particle(s).
In quantum mechanics, particles are described by a mathematical representation called a quantum state. A quantum state contains all the information about a particle's properties, such as its position, momentum, or spin. In a classical system, each particle has its own independent state, and the states of different particles can be described separately. However, in a quantum entangled system, the quantum states of the particles are no longer independent and must be described collectively.
The defining feature of entanglement is that the quantum states of entangled particles are highly correlated, regardless of the distance between them. This correlation means that measuring one particle's property instantaneously determines the corresponding property of the other particle, even if they are far apart. This seemingly non-local connection is often referred to as "spooky action at a distance."
The behavior of entangled particles is fundamentally different from classical systems. In classical physics, correlations between particles are limited by local interactions and information exchange, but in entangled quantum systems, these correlations can exist instantaneously over long distances. Additionally, entanglement allows for phenomena such as quantum superposition and quantum teleportation, which have no classical analogues.
Entanglement is a crucial resource in quantum information processing and quantum computing. It enables the development of quantum algorithms, secure communication protocols, and novel technologies like quantum cryptography. The study of entanglement continues to be an active area of research in both theoretical and experimental physics, with implications for various fields such as quantum mechanics, quantum field theory, and quantum gravity.