Long-range coupling between superconducting dots induced by periodic driving

TL;DR

This paper demonstrates that applying periodic voltages to a Josephson bijunction with quantum dots induces long-range interdot coupling via multiple Andreev reflections, extending coupling beyond the superconducting coherence length.

Contribution

It introduces a mechanism for long-range coupling in superconducting quantum dot systems driven periodically, modeled by an effective non-Hermitian Hamiltonian.

Findings

Long-range coupling enabled by periodic driving.

Mechanism involves multiple Andreev reflections and quasiparticle propagation.

Effective non-Hermitian Hamiltonian describes the coupled resonances.

Abstract

We consider a Josephson bijunction consisting of three superconducting reservoirs connected through two quantum dots. In equilibrium, the interdot coupling is sizable only for distances smaller than the superconducting coherence length. Application of commensurate dc voltages results in a time-periodic Hamiltonian and induces an interdot coupling at large distances. The basic mechanism of this long-range coupling is shown to be due to local multiple Andreev reflections on each dot, followed by quasiparticle propagation at energies larger than the superconducting gap. At large interdot distances we derive an effective non-Hermitian Hamiltonian describing two resonances coupled through a continuum.