This article tries to explain what is so "spooky" about quantum entanglement. The "spookiness" comes from Einstein's description of quantum mechanics which he showed, via the EPR-type measurement, that information about a quantum property can be "transferred" instantaneously between entities across space.
You'll notice that in the article, the author had to go back and explain the concept of superposition of states. This is what makes this type of phenomenon different than the classical phenomenon.
If you had been following this blog for a while, this is the same attempt that I made to explain quantum entanglement before. This is because most people who are just trying to understand this only pay attention to the "entanglement" aspect of it, i.e. a property being "linked" over a distance, rather than actually understanding the superposition concept, which is actually more well-established. It is the presence of superposition, and the lack of classical realism on a system (before a measurement) that separates this from an ordinary classical conservation-of-quantity phenomenon.Let’s go over the issue of entanglement to start. The experiment is normally done with photons: you pass a single quantum of light through a specialized material (e.g., a down-conversion crystal) which splits it into two photons. These photons will be entangled in a particular sense, where one has a spin, or internal angular momentum, of +1, and the other has a spin of -1. But you don’t know which is which. In fact, there are some experiments you can do where, if you had large numbers of these photons, you’d see a difference between:
- the statistical results if the spin was +1,
- the statistical results if the spin was -1,
- or the statistical results if the spin was undetermined.