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. It represents a key element for quantum technologies based on phase coherence. Here we demonstrate 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. We 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 effect1,2. We apply an external in-plane magnetic field and, thereby, achieve continuous tuning of φ0. Hence, we can charge and discharge the quantum phase battery. The observed symmetries of the anomalous Josephson effect in the vectorial magnetic field are in agreement with our theoretical model. Our results demonstrate 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.
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The data that support the findings of this study are available from corresponding author E.S. upon reasonable request.
The codes that support the findings of this study are available from corresponding author F.S.B. upon reasonable request.
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The work of E.S. was supported by a Marie Curie Individual Fellowship (MSCA-IFEF-ST no. 660532-SuperMag). E.S., N.L. and F.G. acknowledge partial financial support from the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC grant no. 615187-COMANCHE. E.S., A.I., O.D., N.L., F.S.B. and F.G. were partially supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 800923 (SUPERTED). L.S. and V.Z. acknowledge partial support by the SuperTop QuantERA network and the FET Open And QC. I.V.T., C.S.F. and F.S.B. acknowledge financial support by the Spanish Ministerio de Ciencia, Innovacion y Universidades through projects no. FIS2014-55987-P, no. FIS2016-79464-P and no. FIS2017-82804-P and by the grant ‘Grupos Consolidados UPV/EHU del Gobierno Vasco’ (grant no. IT1249-19). A.B. thanks the CNR-CONICET cooperation programme ‘Energy conversion in quantum nanoscale hybrid devices’; the SNS-WIS joint laboratory QUANTRA, funded by the Italian Ministry of Foreign Affairs and International Cooperation; and the Royal Society through the international exchanges between the United Kingdom and Italy (grant no. IEC R2192166).
The authors declare no competing interests.
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Strambini, E., Iorio, A., Durante, O. et al. A Josephson phase battery. Nat. Nanotechnol. 15, 656–660 (2020). https://doi.org/10.1038/s41565-020-0712-7