Hua Nan

Quantum entanglement is a fragile thing. Two friends move to different cities, each carrying a box with one of a pair of gloves: if one box has the left glove, the other has the right. Entangled particles behave similarly, except that until measurement, no one knows which is where.

Any battery, from a AA to a quantum one, is simple in principle: there's a store of energy, and there's a way to get it out. In the quantum world, this 'way' looks like a careful switching between particle states, akin to moving a ball from a high shelf to a low one.