- Scientists have confirmed a long-standing rule of quantum physics.
- For the first time, researchers were able to see experimentally that the information shared between quantum subsystems depends on surface area, not volume.
- This is very different from the way particles interact in the non-quantum world, where measuring one particle or one subsystem tells you nothing about another.
It is sharing and sharing alike in the quantum world, but only on a surface level. A group of scientists has just managed to experimentally confirm a long-standing paradoxical rule of quantum systems: they can share information, but how much depends on the surface area of the system, not its volume.
This may seem like a “so what?” at first, but it is remarkably different from the way we see our world. To quote an analogy from a press release about the result, “the information contained in a book depends on its volume—not just the area of the book’s cover. In the quantum world, however, information is often tightly bound to the surface.”
This relationship depends on an idea called “mutual information”. This is key in quanta, and is the idea that if two particles are close enough (within a short distance called the “coherence length”) and behave quantumly, measuring one particle will give you information about another. In our non-quantum world, it would be like meeting someone new and suddenly knowing the name of the person standing right next to them. And it’s not just particle to particle – it can be between two subsystems in the same system.
Subsystem to subsystem is where surface connection comes in. No matter how much information is contained in one subsystem, the only data that can be transferred to the particles in the neighboring subsystem is from the particles right at the surface where the two meet. Anything from further back in the quantum cloud cannot be transferred to the new subsystem. It’s a print rather than a download.
To prove this, the researchers took gas in a container and cooled it to as close to absolute zero as possible. At temperatures like this, particles stop behaving the way they do in the everyday world at everyday temperatures and start behaving quantumly, sharing their information. The researchers then turned on the gas.
Not literally, but they messed up the gas. “It’s like throwing a stone into a lake and then getting information about the state of the liquid and the lake from the subsequent waves,” Jörg Schmidtmeier, one of the study’s researchers, said in a press release.
Once the gas was broken through, the researchers were able to use specially developed techniques to see how the atoms in the gas interact quantumly with each other and were able to demonstrate that the information shared depends on surface area instead of volume. They were also able to confirm that temperature has an effect on this “coherence length” distance of information sharing. Heat a particle too much and the coherence disappears. Reduce it to almost absolute zero and it pops back up.
Confirmation of this connection for surface area and information sharing has major implications in a wide range of quantum fields, ranging from quantum gravity to solid-state physics. We still have a lot to learn about quantum physics, but every time we can confirm that we were right about something, we get one step closer to completing the picture.
Associate News Editor
Jackie is a writer and editor from Pennsylvania. She especially enjoys writing about space and physics and enjoys sharing the strange wonders of the universe with anyone who will listen. She is watched over in her home office by her two cats.