Soliton capacitors in a Cooper-pair box transmission line

We propose a superconducting circuit that supports the propagation of Korteweg--de Vries (KdV)-type voltage solitons. By employing Cooper-pair boxes as nonlinear capacitors, we realize a dual system to the previously reported current solitons based on nonlinear inductors. The proposed voltage solitons manifest as propagating capacitors, carrying a velocity-dependent induced charge. This unique characteristic facilitates local electrostatic interactions, which are dual to the magnetic interactions mediated by fluxons.