I'd disagree with the statement "we know what it is". What we know are the symptoms of QE when we see them. What we DON'T know is WHY it happens, since it doesn't fit into our models of how the world works. It's like the two-slit experiment, where light is both a particle and a wave... we can demonstrate it, but we don't know why it happens. So we can currently point at something that makes no sense and say "that's quantum entanglement", but we cannot say how it works or why ... and then on to your next question; is it something we can use in some way? I hope I live long enough to learn the mechanics of how QE works... "But... we know what quantum entanglement is. Quantum entanglement is quantum entanglement. We have the mathematics that allow us to describe the relatively complex system of two entangled atoms, and we have obviously designed an experimental setup and procedure that allows us to do it."