LQC QuaCR Proposals: Theory of Spin and Majorana Qubits
Abstract
Here, QuaCR candidates Merritt Losert and Ben Woods propose to theoretically advance the materials systems, device designs, and fundamental understanding of several types of semiconductor-based qubits, within the research group of PI Mark Friesen. Graduate student Merritt Losert proposes to employ tight-binding, effective-mass, configurationinteraction, and machine-learning techniques to explore several questions of fundamental interest for silicon-based quantum-dot spin qubits. First, he will perform device-level simulations to characterize the interplay between two kinds of atomistic disorder and their effect on the conduction-band-valley energy splitting. These include atomic steps at the Si/SiGe quantum well interface and Ge concentration fluctuations due to alloy disorder. Currently, there is no detailed understanding of the latter phenomena; however, MerrittÕs initial explorations suggest that it is likely to be the dominant source of valley-orbit coupling in all existing devices. The results of these calculations will inform the silicon qubit community on target goals for heterostructure growth, and the ultimate variability that one may expect for statistical variations of the valley splitting in scaled-up qubit devices. Merritt will also explore single-qubit and multi-qubit systems in Si dots comprised of many electrons. Such multi-electron dots are currently of great interest within the community because of their potential for screening out environmental charge noise, due to the formation of inert Òclosed shells.Ó However theoretical treatments of quantum many-body effects in such systems are computationally expensive, using conventional techniques. Merritt will overcome these hurdles by employing machine-learning techniques developed by quantum chemists. He will benchmark his results against the gold-standard configurationinteraction method, in the few-electron limit. The outcome of this work will provide an understanding of how far experimentalists can push their qubits into the multi-electron regime. Postdoc Ben Woods brings considerable device-level modeling experience to the Friesen group. He will apply these tools to the problem of enhancing spin-orbit coupling and controlling the g-factor in silicon or germanium-based qubits. Such results are of great interest to the community because they obviate the need for micromagnets in current qubit designs; the latter represents one of the main obstacles for scale-up in these systems. Ben will employ band-structure calculation methods to understand the recent observation of g-factors deviating significantly from 2 in the UW-Madison Wiggle-Well experiment. Additionally, Ben will explore novel types of hybrid semiconductor-superconductor systems in the hunt for Majorana-type topologically protected qubits. While considering a variety of semiconducting systems, he will focus on the Ge quantum-well, hole-based systems currently being explored experimentally at UW-Madison in the Eriksson group. Ben is currently developing a very clever idea to use time-reversalinvariant schemes to provide the required p-wave proximitized superconductivity without needing to apply an external magnetic field. Since magnetic fields quench superconductivity, they represent the greatest challenge for conventional Majorana-based schemes; BenÕs proposal bypasses this issue and will therefore be of great interest to the community. Ben will also explore superlattice schemes for enhancing the gfactor in Ge-based Majorana qubits, which would allow the qubits to be formed in the presence of a much Ge-based Majorana qubits, which would allow the qubits to be formed in the presence of a much smaller applied magnetic field. Since this second idea falls into the ÒconventionalÓ Majorana qubit category, it will also be of great interest to the community.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 12, 2022
- Source ID
- W911NF2210090
Entities
People
- Mark Friesen
Organizations
- Army Contracting Command
- National Security Agency
- University of Wisconsin–Madison