Probing individual split Cooper-pairs using the spin qubit toolkit

TL;DR

This paper proposes a method using quantum dot spin qubits to experimentally confirm the spin-singlet entanglement of individual split Cooper pairs emitted from a superconductor.

Contribution

It introduces a novel experimental approach to verify the spin state and entanglement of split Cooper pairs using existing quantum dot spin qubit techniques.

Findings

Method to confirm spin-singlet character of Cooper pairs

Utilizes charge measurements on quantum dots as spin state indicators

Proposes a feasible experimental setup with current quantum dot technology

Abstract

A superconductor is a natural source of spin-entangled spatially separated electron pairs. Although the first Cooper-pair splitter devices have been realized recently, an experimental confirmation of the spin state and the entanglement of the emitted electron pairs is lacking up to now. In this paper a method is proposed to confirm the spin-singlet character of individual split Cooper pairs. Two quantum dots (QDs), each of them holding one spin-prepared electron, serve as the detector of the spin state of a single Cooper pair that is forced to split when it tunnels out from the superconductor to the QDs. The number of charges on the QDs, measured at the end of the procedure, carries information on the spin state of the extracted Cooper pair. The method relies on the experimentally established toolkit of QD-based spin qubits: resonant spin manipulation, Pauli blockade, and charge measurement.