At Last, Scientists Have Measured a Paradoxical Quantum Phenomenon

It’s share and share alike in the quantum world, but only at a surface level. A group of scientists just managed to experimentally confirm a longstanding paradoxical rule of quantum systems: they can share information, but how much depends on the surface area of a system, not on its volume.
That might seem like a “so what?” at first, but it’s remarkably different from the way we view our world. To quote an analogy from a press release on the result, “the information contained in a book depends on its volume—not merely on the area of the book's cover. In the quantum world, however, information is often closely linked to surface area.”
That relationship hinges on an idea called “mutual information.” It’s key in quantum, and it’s the idea that if two particles are close enough (within a short distance called the “coherence length”), and behaving quantumly, measuring one particle will tell you information about another. In our non-quantum world, this would be like being introduced to someone new, and suddenly also knowing the name of the person standing right next to them. And this isn’t just particle to particle—it can also be between two subsystems in the same system.
At Last, Scientists Have Measured a Paradoxical Quantum Phenomenon