Voltage-controlled semiconductor nanowire-based superconducting qubits
Abstract
The overall objective of the proposed work is to explore a new type of superconducting qubit for quantum computing. The qubit, termed a Ògatemon,Ó is composed of a semiconductor nanowire with a superconducting shell. A small portion of the shell is etched which allows for control of the qubit via an applied voltage. The proposed research will investigate the fundamental physics of relaxation and dephasing of this new type of qubit and consider how to improve gate fidelities, stability, and performance, all crucial metrics for quantum computing. These objectives will be the focus of years one and two of the project. The proposed objective of the third year is to consider approaches to scaling a system composed of gatemon qubits. The overall proposed approach is based on simplifying the architecture of multiple qubit devices by utilizing a new type of superconducting qubit which can be controlled by voltage rather than by magnetic flux. This new type of qubit represents a departure from previous superconducting qubits in that it does not rely on aluminum oxide as a tunneling barrier in a Josephson junction but rather on a small semiconducting nanowire coated in an epitaxially grown superconducting shell. A small portion of the superconducting shell (<200 nm) is selectively etched away and the resulting qubit can be controlled by applying voltages to a nearby gate. This new type of qubit is called a Ògatemon.Ó Voltage controlled gatemons potentially have an enormous advantage over flux controlled superconducting qubits because voltage lines do not dissipate power and thus do not need to overcome the heating problems inherent in flux controlled systems. Gatemons have already been successfully fabricated and the approach of this research will be to explore their viability as qubits by studying their relaxation and dephasing properties along with methods to improve their fidelity, stability, and performance. For the first two years of the program efforts will specifically focus on optimizing junction design and exploring decoherence and noise in various single-qubit and few-qubit schemes. The junction design work will examine current-phase relationships and methods for reducing nanowire disorder and charge noise, work to understand quasiparticle tunneling in gatemon systems and its relation to coherence, and explore using multi-gate geometries to control potentials along the nanowires. The decoherence and noise work will characterize sources of decoherence and explore how decoherence depends on fabrication, layout, materials, and mitigation schemes. The third and final year of the project will shift focus away from single or few qubit geometries and consider approaches to scaling quantum computing systems designed with gatemons. The voltage control enabled by the gatemon is poised to reduce complexity in wiring, reduce the footprint of superconducting qubit systems, facilitate routing through complex structures, and reduce cross talk due to the screening of electric fields. While much of this work will still take place with smaller multi-qubit systems, the goal is to develop approaches to move toward scalable layouts and geometries.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 12, 2017
- Source ID
- W911NF1610027
Entities
People
- Charles Marcus
Organizations
- Army Contracting Command
- National Security Agency
- University of Copenhagen