Quantum Coulomb drag mediated by cotunneling of fluxons and Cooper pairs

TL;DR

This paper predicts two quantum Coulomb drag effects in Josephson circuits caused by cotunneling of fluxons and Cooper pairs, revealing new quantum transport phenomena in superconducting systems.

Contribution

It introduces two novel quantum Coulomb drag effects mediated by cotunneling processes in Josephson circuits, expanding understanding of quantum transport in superconducting devices.

Findings

Biasing one junction induces voltage in another via fluxon cotunneling.

Cooper pair cotunneling causes dual drag effect in series Josephson junctions.

Effects occur in both superconducting and insulating regimes.

Abstract

We predict two novel quantum drag effects which can occur in macroscopically quantum coherent Josephson circuits. We demonstrate that biasing one resistively shunted Josephson junction by an external current one can induce a non-zero voltage drop across another such junction capacitively coupled to the first one. This quantum Coulomb drag is caused by cotunneling of magnetic flux quanta across both junctions which remain in the "superconducting" regime. Likewise, Cooper pair cotunneling across a pair of connected in series Josephson junctions in the "insulating" regime is responsible for another -- dual -- quantum Coulomb drag effect.