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| Physicists in Finland and Russia have shown how graphene quantum dots can be used to split Cooper pairs. (Courtesy: Shutterstock/Mopic) |
Superconducting "Cooper pairs" of electrons have been split to create entangled pairs of electrons in a new device built by physicists in Finland and Russia. The device employs two quantum dots made of graphene. Although other types of quantum dots have been used for this purpose, the latest research suggests that graphene quantum dots should deliver long-lived entangled electron pairs that could be used in quantum computers.
Entanglement is a quantum-mechanical phenomenon in which properties of fundamental particles are correlated so that making a measurement on one particle can instantaneously affect another particle – even across very large distances. In principle, a quantum computer can use this connectedness to perform certain calculations much faster than a conventional computer. Although practical quantum computers do not exist today, some potential designs involve using the intrinsic angular momenta, or "spin", of electrons as quantum bits (qubits) of information that can be entangled.
Superconductors provide a ready source of entangled electrons because the Cooper pairs that allow these materials to conduct electricity with little or no resistance are in fact entangled pairs of electrons with opposite spin. Splitting the pairs while preserving the electrons' entanglement can be done simply by connecting ordinary metal wires to either end of the superconductor. If the set-up is just right, each wire will carry away one electron from a pair. However, it is more often the case that both electrons will end up going down the same wire.
Physics World: Graphene quantum dots split Cooper pairs, Edwin Cartlidge
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