For the first time, a pair of electrons have been detected temporarily inhabiting higher orbital states than normal. Although the phenomenon has long been predicted by quantum physics, it was thought nearly impossible to observe. The achievement may allow for a better understanding of superconductivity, in turn improving high-temperature superconducting devices.
Electrons associated with atoms have multiple energy levels, known as orbitals. Extra energy provided by collisions with photons can bump an electron to a higher orbital, before it drops back down again, releasing energy in the process. One of the features of quantum mechanics is that in multi-electron systems, pairs of electrons sometimes briefly hop to higher orbitals than their energy should classically allow.
The phenomenon is thought to be related to superconductivity, where two electrons' coherence keeps them moving endlessly through very cold materials. However, observing it was always going to be difficult, not just because of the size of the objects in question, but because it is rare. Professor Anatoli Kheifets of the Australian National University told IFLScience that in hydrogen molecules, at any given time there is a roughly 1 percent probability that the electron pair will be in the first raised orbital, and an even lower chance that it'll be somewhere higher. “Scientists never thought they could observe such a rare event,” Kheifets said in a statement.
In order to catch the process in action, Kheifets and other scientists beamed X-Rays at two hydrogen atom molecules, knocking one of the electrons from the system. Since the electrons help bind the molecules together, removing an electron causes the two hydrogen atoms to separate, leaving one hydrogen atom, a proton, and the knocked-out electron. However, as the team report in Nature Communications, the removed electron and the one still part of an atom remain entangled, so anything we learn about one tells us about the state of the other.
The authors then measured the energy of the removed electron, and orbital parameters of the surviving atom, creating a clear (to quantum physicists) picture of the state of the electrons when in the higher orbital.
In an effort to enable the rest of the world to understand the weird behavior, Kheifets drew an analogy with a pair of humans bound to each other, but still in need of some space. Going to a higher orbital is like a vacation for the electrons. It costs energy, the subatomic equivalent of money. Two electrons simultaneously in higher orbitals is analogous to couples going on holiday at the same time, but in different places to give each other space. It costs even more, but the room each gives the other helps them stay together in the long term.
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