Yu-Shiba-Rusinov qubit

TL;DR

This paper proposes a YSR qubit based on magnetic impurity states in superconductors, demonstrating its controllability, robustness against noise, and potential for quantum computing applications involving Majorana states.

Contribution

It introduces a novel YSR qubit model, deriving its effective Hamiltonian and analyzing its control, readout, and coherence properties in superconducting systems.

Findings

YSR qubit can be controlled and read out with current experimental techniques.

The YSR qubit exhibits robustness against spin noise over a wide parameter range.

Potential integration with Majorana qubits for universal quantum gate implementation.

Abstract

Magnetic impurities in $s$-wave superconductors lead to spin-polarized Yu-Shiba-Rusinov (YSR) in-gap states. Chains of magnetic impurities offer one of the most viable routes for the realization of Majorana bound states which hold a promise for topological quantum computing. However, this ambitious goal looks distant since no quantum coherent degrees of freedom have yet been identified in these systems. To fill this gap we propose an effective two-level system, a YSR qubit, stemming from two nearby impurities. Using a time-dependent wave-function approach, we derive an effective Hamiltonian describing the YSR qubit evolution as a function of distance between the impurity spins, their relative orientations, and their dynamics. We show that the YSR qubit can be controlled and read out using the state-of-the-art experimental techniques for manipulation of the spins. Finally, we address the effect of the spin noises on the coherence properties of the YSR qubit, and show a robust behaviour for a wide range of experimentally relevant parameters. Looking forward, the YSR qubit could facilitate the implementation of a universal set of quantum gates in hybrid systems where they are coupled to topological Majorana qubits.