Topic II.A.1.a: Novel superconducting MgB2 nanowire-based qubits constructed by scanning tunneling microscope electron beam induced decomposition of newly developed CVD precursors
Abstract
Traditional superconducting qubits employ a superconductor-insulator-superconductor Josephson junction. This design relies on the extremely difficult challenge of creating an insulating junction that is both extremely thin (around one nanometer) and of high uniformity and purity. A n alternative approach - and one that may be easier to implement- is to construct qubits from superconducting nanowires: if such a wire is sufficiently narrow in diameter, on the order of a few nanometers in size, it should take on the properties of a nonlinear inductor and hence should act as a qubit, even with no oxide present. The current proposal will address the twin challenges of making such ultrathin nanowires of superconducting materials and demonstrating that they can indeed serve as functional qubits. Scanning tunneling microscope (STM) based lithography techniques are able to modify surfaces with atomic precision, and the development of low temperature chemical vapor deposition (CVD) precursors has made it possible to grow materials under relatively mild conditions of just a few hundred degrees Celsius. Combining STM lithography with CVD precursors has already made it possible to grow non-superconducting metallic nanowires and dots of phases such as HfB2, with dimensions as small as a few nanometers. We will apply knowledge we have gained in studies of the direct writing of nanoscale metallic Hffi2 features to establish methods for writing extremely fine superconducting nanowires by use of STM lithography in an ultrahigh vacuum (UHV) STM. Specifically, we propose to use STM lithography to fabricate superconducting nanowires ofMgB2, vanadium-doped HfB2, MoCN and other superconducting materials by employing both existing low temperature CVD precursors, as well as improved precursors - optimized for STM lithography -that we will develop in the course of the work plan. We will fabricate two types of qubits based on these nanowires: a nanowire transmon qubit and a phase slip qubit, and investigate their performance with the aid of a c-QED 3 D microwave cavity. The research goals will be achieved by means of an iterative process that involves feedback among the following tasks: (1) the synthesis of existing and improved low temperature precursors for the STM lithography superconducting materials; (2) evaluation of the abilities of these precursors to deposit superconducting phases; (3) use of the developed precursors to create superconducting nanowires by scanning tunneling microscope lithography; and (4) evaluation and testing of these nanowires in qubit structures. The outcome of this project will be the creation of nanowire qubits for use in quantum computing systems. Among the specific goals to invent new low temperature molecular precursors for superconductors that are optimized for use in STM lithography, and which will open a new realm of availability and ease for producing superconducting films and wires, to fabricate superconducting nanowires with dimensions that are considerably smaller than those that have been studied to date for qubit applications. Our ultimate goal is to develop qubits with coherence times significantly longer than the best characteristics of superconducting qubits demonstrated so far, for example in the millisecond range in the case of transmon qubits. The results have the potential to be far-reaching and enabling.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 11, 2018
- Source ID
- W911NF1810117
Entities
People
- Joseph W Lyding
Organizations
- Army Contracting Command
- National Security Agency
- University of Illinois Urbana–Champaign