Batteries belongs to everyday life. A classical battery, the Volta's pile, converts chemical energy into a voltage, which can power electronic circuits. In many quantum technologies, circuits or devices are based on superconducting materials. In such materials, currents may flow without the need of an applied voltage; therefore, there is no need for a classical battery in such a system. These currents are called supercurrents because they do not exhibit any energy losses. They are induced not from a voltage but from a phase difference of the wave function of the quantum circuit, which is directly related to the wave nature of matter. A quantum device able to provide a persistent phase difference can be seen as a quantum phase battery, which induces supercurrents in a quantum circuit.
In this work, the authors present the results from a theoretical and experimental collaboration that has led to the fabrication of the first quantum phase battery. The idea was first conceived in 2015, by Sebastian Bergeret from the Mesoscopic physics group at the Materials Physics Center (CFM, CSIC-UPV/EHU), a joint initiative of Consejo Superior de Investigaciones Científicas (CSIC) and the University of the Basque Country (UPV/EHU), and Ilya Tokatly, Ikerbasque Professor in the Nano-Biospectroscopy group of the UPV/EHU, both Donostia International Physics Center (DIPC) associate researchers. They proposed a theoretical system with the properties needed to build the phase battery. It consists of a combination of superconducting and magnetic materials with an intrinsic relativistic effect, called spin-orbit coupling.
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