Transporting a single-spin qubit through a double quantum dot

TL;DR

This paper analyzes errors in transporting a single-spin qubit through a double quantum dot, focusing on leakage sources like ramping times, spin-orbit effects, and valley states, and proposes pulse shaping techniques to minimize errors.

Contribution

It provides a systematic framework for estimating and minimizing leakage errors during spin qubit transport in semiconductor quantum dots, including pulse design strategies.

Findings

Leakage errors can be quantitatively estimated for different transport scenarios.

Carefully designed spin rotations can significantly reduce leakage errors.

Pulse shaping constraints improve the fidelity of spin qubit transport.

Abstract

Coherent spatial transport or shuttling of a single electron spin through semiconductor nanostructures is an important ingredient in many spintronic and quantum computing applications. In this work we analyze the possible errors in solid-state quantum computation due to leakage in transporting a single-spin qubit through a semiconductor double quantum dot. In particular, we consider three possible sources of leakage errors associated with such transport: finite ramping times, spin-dependent tunneling rates between quantum dots induced by finite spin-orbit couplings, and the presence of multiple valley states. In each case we present quantitative estimates of the leakage errors, and discuss how they can be minimized. Moreover, we show that in order to minimize leakage errors induced by spin-dependent tunnelings, it is necessary to apply pulses to perform certain carefully designed spin rotations. We further develop a formalism that allows one to systematically derive constraints on the pulse shapes and present a few examples to highlight the advantage of such an approach.