A Josephson phase battery
A classical battery converts chemical energy into a persistent voltage bias that can power electronic circuits. Similarly, a phase battery is a quantum device that provides a persistent
phase bias to the wave function of a quantum circuit. In their paper, Francesco Giazotto and co-worker from Istituto Nanoscienze-CNR and Scuola Normale Superiore, at NEST Pisa and other collaborators in Italy, Spain, and USA, demonstrated on NATURE NANOTECHNOLOGY a “phase battery” in a hybrid superconducting circuit.
It consists of an n-doped InAs nanowire with unpaired-spin surface states, that is proximitized by Al superconducting leads. They find that the ferromagnetic polarization of the unpaired-spin states is efficiently converted into a persistent phase bias φ0 across the wire, leading to the anomalous Josephson effect. They apply an external in-plane magnetic field and, thereby, achieve continuous tuning of φ0. Hence, in their paper they demonstrate that it is possible to charge and discharge the quantum phase battery. The observed symmetries of the anomalous Josephson effect in the vectorial magnetic field are also in agreement with theit theoretical model.
Therefore, the paper demonstrates how the combined action of spin–orbit coupling and exchange interaction induces a strong coupling between charge, spin and superconducting phase, able to break the phase rigidity of the system. It represents a key element for quantum technologies based on phase coherence.
More details can be found HERE.