Lifetime of Majorana qubits in Rashba nanowires with non-uniform chemical potential

TL;DR

This paper investigates how non-uniform chemical potentials in Rashba nanowires hosting Majorana qubits lead to subgap states that significantly reduce qubit lifetime at finite temperatures due to thermal excitations.

Contribution

It provides a detailed analysis of Majorana qubit lifetime reduction caused by local trivial phase regions and subgap states in non-uniform chemical potential nanowires using Keldysh formalism.

Findings

Subgap Andreev bound states emerge at topological-trivial interfaces.

Majorana qubit lifetime is significantly shortened by thermal noise.

Non-uniform chemical potential decreases qubit stability compared to uniform cases.

Abstract

We study the lifetime of topological qubits based on Majorana bound states hosted in a one-dimensional Rashba nanowire (NW) with proximity-induced superconductivity and non-uniform chemical potential needed for manipulation and read-out. If nearby gates tune the chemical potential locally so that part of the NW is in the trivial phase, Andreev bound states (ABSs) can emerge which are localized at the interface between topological and trivial phases with energies significantly less than the gap. The emergence of such subgap states strongly decreases the Majorana qubit lifetime at finite temperatures due to local perturbations that can excite the system into these ABSs. Using Keldysh formalism, we study such excitations caused by fluctuating charges in capacitively coupled gates and calculate the corresponding Majorana lifetimes due to thermal noise, which are shown to be much shorter than those in NWs with uniform chemical potential.