Quantum Physics

Track 11: Quantum entanglement

Quantum entanglement is one of the uber-bizarre phenomena seen when things get itty-bitty, or inside the quantum realm. No matter how far apart two or more particles are in space, their states remain linked when they hook up in a specific way. That indicates that they are in a single, shared quantum state. Therefore, regardless of how far apart the particles are, observations of one of the particles can automatically reveal information about the other entangled particles. Furthermore, any change to one of these particles will inevitably have an effect on the others in the entangled system.

Physicists developed the fundamental ideas behind entanglement as they worked out the mechanics of the quantum world in the early decades of the 20th century. They found that to properly describe subatomic systems, they had to use something called a quantum state.

In the quantum world, nothing is ever known for certain; for example, you never know exactly where an electron in an atom is located, only where it might be. A quantum state summarizes the probability of measuring a certain property of a particle, like its position or angular momentum. So, for example, the quantum state of an electron describes all the places you might find it, together with the probabilities of finding the electron at those places.