Strong Charge-Photon Coupling in Planar Germanium Enabled by Granular Aluminium Superinductors

• URL: http://arxiv.org/abs/2407.03079v1
• Date: Wed, 3 Jul 2024 12:53:01 GMT
• Title: Strong Charge-Photon Coupling in Planar Germanium Enabled by Granular Aluminium Superinductors
• Authors: Marián Janík, Kevin Roux, Carla Borja Espinosa, Oliver Sagi, Abdulhamid Baghdadi, Thomas Adletzberger, Stefano Calcaterra, Marc Botifoll, Alba Garzón Manjón, Jordi Arbiol, Daniel Chrastina, Giovanni Isella, Ioan M. Pop, Georgios Katsaros,
• Abstract summary: We have integrated a granular aluminium resonator with a characteristic impedance exceeding the resistance quantum. We demonstrate strong charge-photon coupling with a rate of $g_textc/2pi= (566 pm 2)$ MHz. This method opens the path for novel qubits and high-fidelity, long-distance two-qubit gates.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: High kinetic inductance superconductors are gaining increasing interest for the realisation of qubits, amplifiers and detectors. Moreover, thanks to their high impedance, quantum buses made of such materials enable large zero-point fluctuations of the voltage, boosting the coupling rates to spin and charge qubits. However, fully exploiting the potential of disordered or granular superconductors is challenging, as their inductance and, therefore, impedance at high values are difficult to control. Here we have integrated a granular aluminium resonator, having a characteristic impedance exceeding the resistance quantum, with a germanium double quantum dot and demonstrate strong charge-photon coupling with a rate of $g_\text{c}/2\pi= (566 \pm 2)$ MHz. This was achieved due to the realisation of a wireless ohmmeter, which allows \emph{in situ} measurements during film deposition and, therefore, control of the kinetic inductance of granular aluminium films. Reproducible fabrication of circuits with impedances (inductances) exceeding 13 k$\Omega$ (1 nH per square) is now possible. This broadly applicable method opens the path for novel qubits and high-fidelity, long-distance two-qubit gates.

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