Scientists at the University of Basel have experimentally demonstrated for the first time that there is a negative correlation between the two spins (The connection between the coupled electrons is shown) of a pair of electrons bound in a superconductor. For their study, the researchers used filters made of nanomagnets and quantum dots, as they report in the scientific journal Nature.
The coupling between two particles is one of the wonders of quantum physics that is difficult to reconcile with everyday experience. If they bind, some properties of the two particles are closely related, even when they are far apart. Albert Einstein described relativity as “frightening behavior at a distance”. Research on the interaction between light particles (pictured) won this year’s Nobel Prize in Physics.
Two electrons can be bound, for example in their spin. In a superconductor, the electrons form what are called Cooper pairs for the electrons to be lost and each other to accumulate.
For several years, researchers from the Swiss Nanoscience Institute and the Department of Physics at the University of Basel have been able to remove pairs of electrons from a superconductor and separate the two electrons. This is achieved by the number of pairs – nanoelectronics are connected to each other, each of them leaves only one electron.
Cooper’s second anti-electron
Members of Prof. Dr Christian Schönenberger and Dr Andreas Baumgartner, in collaboration with the researchers of Prof. Dr Lucia Sorba of the Istituto Nanoscienze-CNR at the Scuola Normale Superiore in Pisa has been able to demonstrate experimentally what was expected in theory: the electrons of the superconductor always appear in pairs and other colors.
Thanks to a new set of experiments, scientists can measure that the spin of electrons points up when others point down, and vice versa. Andreas Baumgartner, project leader, explains: ‘We have experimentally demonstrated the negative interaction between coupled electrons.
The researchers achieved this using a pin filter they developed in their lab. Using a small magnet, they create a magnetic field between two quantum dots that separates electrons in Cooper pairs. Since the spin also determines the magnetic moment of the electron, only one type of spin is allowed at a time.
“We were able to manipulate the two quantum dots so that most of the electrons have a small sample size passing through them,” says first author Dr Arunav Bordoloi. “For example, an electron with a higher spin passes through one quantum dot and an electron with a lower spin passes through the other quantum dot, or vice versa. If the two quantum dots are observed to emit only one spin, the electric potential in both quantum dots is reduced, even though an electron can pass successfully through one quantum dot.
“With this method, we can detect such a negative interaction between the electronics of a superconductor for the first time,” concluded Andreas Baumgartner. “Our experiment is a first step, but not a definitive proof of the addition of electrons, because we can’t define the reverse mechanism of the filter – but we are working on it.”
This research, which was recently published in Nature, is seen as an important step forward in the experimental study of quantum mechanical phenomena, such as particle collisions in solids, which are also the main components of quantum computers.
