Quantum entanglement between electrons and ions captured at attosecond timescale

Quantum mechanics is extremely successful at describing the behavior of matter at the atomic level. This success forces one to accept that certain aspects of physical reality go far beyond our intuition. Among these, none is more intriguing than the concept of quantum entanglement, which mathematically describes how two particles that have at some point in the past interacted with each other retain a memory of this interaction to such an extent that acting on one of the two particles has a measurable influence on the properties of the other particle, even if the two have long ago stopped interacting and may be separated by such a vast distance that communication between them is no longer possible.