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Sketched Nanoscale KTaO3-Based Superconducting Quantum Interference Device

Muqing Yu1, Nicholas Hougland1, Qianheng Du2, Junyi Yang2, Sayanwita Biswas1, Ranjani Ramachandran1, Dengyu Yang1, Anand Bhattacharya2, David Pekker1 et al.

Patrick Irvin1 and Jeremy Levy1,*

  • *Contact author: jlevy@pitt.edu
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Phys. Rev. X 15, 011037 – Published 20 February, 2025

DOI: https://doi.org/10.1103/PhysRevX.15.011037

Abstract

The discovery of two-dimensional superconductivity in LaAlO3/KTaO3 (111) and (110) interfaces has raised significant interest in this system. In this paper, we report the first successful fabrication of a direct current superconducting quantum interference device (dc-SQUID) in the KTO system. The key device elements, superconducting weak links, are created by conductive atomic force microscope lithography, which can reversibly control the conductivity at the LAO/KTO (110) interface with nanoscale resolution. The periodic modulation of the SQUID critical current Ic(B) with magnetic field corresponds well with our theoretical modeling, which reveals a large kinetic inductance of the superconducting two-dimensional electron gas in KTO. The kinetic inductance of the SQUID is tunable by electrical gating from the back, due to the large dielectric constant of KTO. The demonstration of weak links and SQUIDs in KTO broadens the scope for exploring the underlying physics of KTO superconductivity, including the role of spin-orbit coupling, pairing symmetry, and inhomogeneity. It also promotes KTO as a versatile platform for a growing family of quantum devices, which could be applicable in the realm of quantum computing and information.

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Popular Summary

Superconducting weak links play a crucial role in quantum computing, serving as nonlinear inductive elements in superconducting microwave circuits. While most existing weak links rely on metallic superconductors such as aluminum, recent discoveries show that potassium tantalate (KTaO3, or KTO) exhibits superconductivity with a transition temperature above 2 K. Unlike metals, KTO is a semiconductor with a low electron density and strong sensitivity to electrical gating, making it a promising alternative for next-generation quantum devices. In this study, we demonstrate the fabrication of superconducting weak links on KTO, highlighting its potential as a novel material platform for quantum computing applications.

To create these weak links, we employ a unique fabrication method using an atomic force microscope tip to reversibly “sketch” nanoscale weak links onto KTO, rather than relying on conventional electron-beam lithography. By placing two of these weak links in parallel, we observe quantum interference effects, confirming the phase coherence between them. Further theoretical analysis reveals that these weak links exhibit an extremely high inductance exceeding >100  nH/μm, attributed to KTO’s low superfluid density and the nanoscale dimensions of the links. Additionally, we demonstrate that the inductance can be tuned via electrical gating from the back side of the sample, a property not typically seen in metallic superconductors.

Our findings establish KTO as a viable platform for quantum devices, particularly in applications requiring large and tunable inductance, such as superinductors, parametric amplifiers, and charge-noise-resistant qubits. The successful integration of KTO with AFM-based nanoscale patterning paves the way for a new family of reconfigurable quantum circuits, offering exciting prospects for the future of quantum computing and information technology.

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Phys. Rev. X 15, 011037– Published 20 February, 2025
  • Received 25 February 2024
  • Revised 16 September 2024
  • Accepted 17 December 2024
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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