What are the proofs of quantum entanglement?

Quantum entanglement is a phenomenon where particles become connected in such a way that the state of one particle is dependent on the state of the other, regardless of the distance between them. The proofs of quantum entanglement are primarily based on experimental demonstrations that violate the principles of classical physics, particularly through the violation of Bell's inequality. Here are some key proofs and experiments:

1. Bell Test

• Description: The Bell test is a series of experiments designed to verify the predictions of quantum mechanics regarding entangled particles. It tests whether the correlations between entangled particles can be explained by local hidden variable theories.
• Outcome: These experiments consistently show that entangled particles exhibit correlations that cannot be explained by classical physics, thus confirming quantum entanglement13.

2. EPR Paradox and Its Resolution

• Description: Initially proposed by Einstein, Podolsky, and Rosen in 1935, the EPR paradox questioned the completeness of quantum mechanics due to its seemingly "spooky action at a distance." However, subsequent experiments resolved this paradox by demonstrating that quantum mechanics accurately predicts the behavior of entangled particles.
• Outcome: Experiments have shown that entangled particles indeed exhibit non-local correlations, supporting quantum mechanics over local realism3.

3. Quantum Teleportation

• Description: Quantum teleportation is a process that relies on entanglement to transfer information about the quantum state of a particle from one location to another without physical transport of the particles themselves.
• Outcome: Successful demonstrations of quantum teleportation further validate the existence and utility of entanglement3.

4. Entanglement with Diverse Particles

• Description: Recent experiments have expanded the scope of entanglement by demonstrating it not just with identical particles but also with particles of opposite charges, such as positively and negatively charged pions2.
• Outcome: This shows that entanglement is a more universal phenomenon than previously thought.

5. Cosmological Evidence

• Description: Researchers have used light from ancient quasars to set up experiments that test quantum entanglement over vast distances, further confirming its validity5.

These experiments collectively provide strong evidence for the reality of quantum entanglement and its role in quantum mechanics.