Continuously Tunable Charge in Andreev Quantum Dots

TL;DR

This paper demonstrates that Andreev quantum dots can trap a continuously tunable fractional charge, controllable through gate potential and phase difference, with implications for quantum charge manipulation.

Contribution

It introduces a method to achieve and control fractional charge in Andreev quantum dots, expanding understanding of charge states in superconducting quantum devices.

Findings

Fractional charge can be continuously tuned via gate potential.

Particle-hole symmetry breaking causes the fractional charge.

Experimental signatures of charge states are identified.

Abstract

We show that a quantum dot connected via tunnel barriers to superconducting leads traps a continuously tunable and hence fractional charge. The fractional charge on the island is due to particle-hole symmetry breaking and can be tuned via a gate potential acting on the dot or via changes in the phase difference across the island. We determine the groundstate, equilibrium, and excitation charges and show how to identify these quantities in an experiment.