Advanced materials for spin-based qubits

 

Principal Investigator: Lars Schreiber

 

Overview

The quality and the reproducibility of spin-qubits hosted in gate-defined quantum dots are intimately related to the quality of the host material and of the fabrication technology. In collaboration with external partners, we investigate how material aspects, such as isotopic composition and crystallographic perfection, affects the performance of spin-qubits in Si/SiGe. Furthermore, we exploring the potential of non-conventional materials such as ZnSe/(Zn,Mg)Se for hosting spin-based qubits and for realizing spin-photon interfaces.

 

Key research areas

High-purity SiGe for quantum circuits

ZnSe as a host for gate-defined spin qubits

 

High-purity SiGe for quantum circuits

Material disorder is one of the main obstacles to the scalability of spin qubit architectures in SiGe-heterostructures, being responsible for charge noise and for the large variability of devices properties. Together with the Leibniz Institute for Crystal Growh (IKZ), the Leibniz Institute for Innovative Microelectronics (IHP) and the Institute of Semiconductor Electronics (IHT), we are developing a non-invasive fabrication process for quantum dots and charge noise meters with minimal impact on the properties of the substrate, which will allow a true optimization of isotopically enriched SiGe/28Si/SiGe heterostructures with high-purity and crystallographic perfection. This project, founded by the Leibniz Collaborative Excellence, aims at providing the material foundations of next generation Si-based spin qubits.

 

ZnSe as a host for gate-defined spin qubits

Schematics of a gate-defined qubit in a ZnSe heterostructure Copyright: L. Schreiber

We explore ZnSe/(Zn,Mg)Se quantum wells as potential hosts for gate defined quantum dots. This material system combines most of the advantages of GaAs (direct band gap leading to strong optical transition, single valley) with those of Si (possibility of isotopic purification for reduced dephasing of electron spin due to nuclear spins), and it has been shown to have favorable properties in optical experiments. However, the realization of gate-defined qubits in ZnSe/(Mg,Zn)Se quantum wells is just in its infancy. The major challenge in this case, is the realization of ohmic contacts on n-type ZnSe with low contact resistance and linear current/voltage dependence extending to low temperature.

Together with the group of Alexander Pawlis at FZ Jülich, which has world-leading experience in the growth of ZnSe heterostructures, we aim at demonstrating gate-defined spin qubits in ZnSe/(Mg,Zn)Se quantum wells and to use them for investigating Spin qubit - optical photon coupling.