Writing Spin in a Quantum Dot with Ferromagnetic and Superconducting Electrodes

TL;DR

This paper introduces a mechanism for writing spin in a quantum dot using Andreev reflection in a ferromagnetic/quantum-dot/superconductor system, enabling controllable spin polarization for quantum computing.

Contribution

It demonstrates that ARISP can be achieved and controlled in a quantum dot system with ferromagnetic and superconducting electrodes, even with Coulomb interactions present.

Findings

Spin polarization depends on ferromagnetic electrode magnetization

Bias voltage controls the sign of spin polarization

ARISP persists with Coulomb interactions when charging energy is comparable to superconducting gap

Abstract

We propose an efficient mechanism for the operation of writing spin in a quantum dot, which is an ideal candidate for qubit. The idea is based on the Andreev reflection induced spin polarization (ARISP) in a ferromagnetic / quantum-dot / superconductor system. We find that on the resonance of Andreev reflection, the spin polarization of quantum dot strongly denpends on the magnetization of ferromagnetic electrode, and the sign of the spin polarization is controllable by bias voltage. In the presence of intradot Coulomb interaction, we show that ARISP effect can still survive as long as the charging energy is comparable to the superconducting gap. Detailed conditions and properties of ARISP are also discussed.