Quantum entanglement is when particles are produced which cannot be described as independent units but instead have a quantum state that must describe all of them simultaneously (for anyone good at maths, here’s a more mathematical description). If two electrons are produced that we know must have total spin zero, then of course one will have spin up and the other spin down. This leads to a seemingly impossible occurrence where the particles seem to be able to communicate information about what has happened to them over arbitrarily long distances instantaneously. The experiments have only ever shown this to be reliably true on the microscopic quantum scale, not surprising considering thermal fluctuations reek havoc upon quantum effects when they aren’t properly controlled, which is very difficult as size increases.
If a stable macroscopic example of quantum entanglement could be found, apart from the much more direct evidence of the world’s quantum nature, it would also allow the change between classical and quantum physics to be properly studied.
This recent paper has looked at the behaviour of two macroscopic scale oscillators that are separated physically but connected by the Coulomb interaction and also the radiation pressure between them. The logarithmic negativity, a representation of entanglement strength, was measured for different coulomb strengths. So long as the value for the entanglement remained above zero, there were some quantum effect between the two mechanical oscillators. It was unsurprisingly found that greater coupling resulted in greater entanglement with the numerical prediction being that no Coulomb interaction would result in no entanglement. This all occurred with no electromechanical forcing present. When this radiation pressure was applied it was found to dominate the interaction to the point where when it was removed the entanglement ceased despite the fact the Coulomb was as strong as ever. The numerical simulations imply that this experiment is stable and robust, far more so then previous ones. Hopefully this will give us a greater grasp on that ever elusive quantum to classical boundary.