Hybrid Epitaxial Semiconductor-Superconductor Qubits
Abstract
Highly coherent superconducting qubits based on Josephson tunnel junctions are the front-runners in the race for a future quantum computer. The highly scalable classical computer chips are based on field-effect transistor technology. The aim of this proposal is to incorporate electrical gating into superconducting qubits in order to simplify quantum gates and thus bring closer the implementation of a functional quantum computer. Our proposal is based on a 2D quantum well heterostructure, where InAs semiconductor is brought to epitaxial contact with superconducting Al. Superconducting proximity effect makes electrons in InAs superconducting as well, while their low density allows for electrical gating. Using a top-down fabrication approach we can pattern a complex network of hybrid super/semi-conductor Josephson junctions whose Josephson energies can be controlled on a nanosecond time scale by gate pulses. We will use these hybrid gate-controlled Josephson junctions to replace conventional AlOx junctions in transmon and fluxonium superconducting qubits. A key feature of our 2D platform is the possibility to make multi-terminal Josephson junctions, where more than 2 superconducting electrodes contact a small size semiconductor region. This allows not only electrical control of qubit frequencies, but also electrical control of qubit-qubit interactions by a simple gate pulse of sufficiently high amplitude. The price of gate control is the more complex spectrum of sub-gap states in the hybrid Josephson junction, which brings more possibilities for decoherence. The main goal of this proposal is to investigate and mitigate decoherence effects associated with the physics of induced superconductivity in a mesoscopic semiconductor. We plan to tackle this problem by forming a tight feedback between molecular beam epitaxy of super/semi heterostructures (Shabani lab), advanced nanofabrication and low-noise transport characterization (Shabani lab, Manucharyan lab), superconducting qubit design and measurement (Manucharyan lab), as well as theory work on mesoscopic superconductivity and decoherence (M. Vavilov, A. Levchenko, R. Joynt). As the decoherence is understood and mitigated, we will progress to fabricating and characterizing hybrid transmons (gatemon) and hybrid fluxoniums and explore two-qubit coupling using the 4-terminal Josephson switches. If successful, our project will not only create a promising avenue to scale up superconducting quantum computing by analogy with transistor integrated circuits, but will also reveal new fundamental physics associated with induced superconductivity in semiconductors at the nanoscale .
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 11, 2018
- Source ID
- W911NF1810115
Entities
People
- Vladimir E Manucharyan
Organizations
- Army Contracting Command
- National Security Agency
- University of Maryland