Developing Quantum Nano-Wire (non-tunnel-junction) Based Superconducting Qubits
Abstract
Nonlinear elements are vital building blocks of quantum circuits as they ensure the non-equidistant energy structure of the system. In the field of superconducting circuits, aluminum-oxide-based Josephson junctions are the ubiquitous nonlinear components which provide the necessary anharmonicity in most circuits. Despite their undeniable success, these elements pose considerable challenges for realizing devices with precisely predictable parameters and inherent noise-protection. The goal of the proposed work is to overcome these limitations by designing, fabricating and characterizing quantum nanowires from amorphous superconductors, which can serve as nonlinear elements for conceptually new qubits (response to funding call A.1.2 & A.1.3). We propose to create weak-link type junctions from multiple high-quality amorphous superconductor materials, including MoSi, MoGe, WSi, and NbSi. These materials have shown excellent properties in single-photon nanowire detectors, indicating the potential for high intrinsic coherence. Leveraging the already existing research and development for these materials at NIST, we will systematically investigate their suitability as nonlinear elements in quantum circuits. Our initial study will involve transport and high-frequency measurements to quantify the nonlinearity of such nanowires made from different materials and with varying geometries, and characterize the loss mechanisms with an emphasis on nonequilibrium quasiparticles. After identifying the most suitable high kinetic inductance material among MoSi, MoGe, WSi, and NbSi, we will incorporate these nanowires into qubits as nonlinear elements. One of the main advantages of these nanowires is that they allow us to fabricate devices in a single lithographic step without relying on highly sensitive oxidation processes. In addition, the absolute minimal number of fabrication steps is beneficial for reaching high-coherence and reproducible qubits. Finally, such weak-links can lead to fundamentally new devices, such as qubits with unconventional potential-energy landscape or quantum phase-slip qubits. One of the outcomes of this project will be a significant advancement in understanding the difference between circuits based on weak-link junctions vs. quantum phase-slip elements. Whether small constrictions can realize the long-sought quantum phase-slip junctions or rather represent a variant of regular Josephson junctions has been an intriguing question for a long time. We will theoretically identify the signatures of these different elements in quantum circuits, and provide a definitive set of circuit-QED measurements to distinguish them from each other. This is a critical step in understanding these non-tunnel junctions and their practical limitations. This step will support the construction of more complex circuits. Among numerous potential applications, the quantum nanowire elements can serve as a platform for circuits with advantageous properties. Building on the non-sinusoidal current-phase relationship provided by them, we propose to realize a transmon-like qubit with enhanced anharmonicity, a small-gap qubit with an underlying double-valley potential that supports simultaneous protection against energy relaxation and dephasing. Finally, using the nanowire as a linear inductor, we propose to construct a coupled fluxonium molecule, which is protected against energy relaxation and global flux noise.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 24, 2022
- Source ID
- W911NF2210050
Entities
People
- Andras Gyenis
Organizations
- Army Contracting Command
- National Security Agency
- University of Colorado Boulder