A Road to Entanglement

At present time, most of the breakthrough technologies are based on the existence of a quantum state called entanglement. Even though this state is a direct prediction from quantum theory, but it turns out that, at the time this state was proposed, it’s very difficult to prove its existence in experiment. Nevertheless nowadays we figure out an efficient way to show this in experiment, which is much easier than what pioneers did in the past, and the theory used to describe this state is also well established than the past and yet there are still a lot more left to study about this state.