Quantum entanglement is a phenomenon in quantum mechanics where two or more particles become interconnected in such a way that the state of one particle instantly affects the state of the other, no matter how far apart they are. This “spooky action at a distance,” as Einstein famously called it, means that the properties of entangled particles are correlated, and changes to one will immediately reflect in the other, even across vast distances.

Key Features of Quantum Entanglement:

1. Non-locality: The effect of one particle on another happens instantaneously, seemingly defying the classical idea that no information can travel faster than the speed of light.
2. Superposition: Each particle in an entangled pair exists in a state of superposition, meaning that its properties (like spin or polarization) are not definite until measured. Once measured, both particles’ states become definite and correlated.
3. Bell’s Theorem: This theory, confirmed by experiments, shows that no local hidden variables can explain the correlations between entangled particles, which means classical physics cannot fully account for this behavior.

Applications:

Quantum entanglement has real-world applications, including:

• Quantum Computing: Entanglement is a key feature in quantum bits (qubits), enabling quantum computers to perform complex calculations more efficiently than classical computers.
• Quantum Cryptography: Entanglement is used in secure communication protocols like quantum key distribution (QKD), which ensures that any attempt to intercept the communication can be detected.
• Teleportation: Quantum entanglement forms the basis of quantum teleportation, where the state of a particle can be transferred to another particle over long distances.

In essence, quantum entanglement defies classical intuition, pointing to the interconnected nature of quantum systems.