Over the past few weeks, we have explored some of the foundational concepts in quantum physics, from quantum jumps to superposition and well beyond. Today we explore what may be the weirdest of quantum effects, that of quantum entanglement, which Einstein called spooky action-at-a-distance. The word says it clearly: To be entangled is to be connected — to have some kind of relation with or dependence on something else.
The dictionary definition is more pragmatic: “cause to become twisted together with or caught in,” like a fish entangled with a net or a person entangled in a difficult situation. Well, pairs of quantum objects — such as pairs of photons, pairs of electrons, or electrons and detectors — do get entangled. And this kind of quantum entanglement is in fact a difficult situation, at least to understand. To grasp what entanglement is, it might be best to apply it to a practical circumstance. If you stay with me, you will get the basics of entanglement and why it is weird.
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