Tomography of a spin qubit in a double quantum dot

TL;DR

This paper develops and compares methods for quantum state tomography of a spin qubit in a double quantum dot, overcoming initial measurement limitations to achieve a complete characterization useful for quantum process analysis.

Contribution

It introduces a general approach to perform comprehensive tomography on solid-state qubits with limited initial measurement bases, validated on a GaAs double quantum dot system.

Findings

Achieved a tomographically complete set of states and measurements

Quantified stochastic and systematic errors in the tomography process

Demonstrated the approach's applicability to spin qubits in quantum dots

Abstract

We investigate a range of methods to perform tomography in a solid-state qubit device, for which a priori initialization and measurement of the qubit is restricted to a single basis of the Bloch sphere. We explore and compare several methods to acquire precise descriptions of additional states and measurements, quantifying both stochastic and systematic errors, ultimately leading to a tomographically-complete set that can be subsequently used in process tomography. We focus in detail on the example of a spin qubit formed by the singlet-triplet subspace of two electron spins in a GaAs double quantum dot, although our approach is quite general.