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

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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Cited by in corpus (6)

• Single-step high-fidelity three-qubit gates by anisotropic chiral interactions
• Theory of superconducting proximity effect in hole-based hybrid semiconductor-superconductor devices
• High Impedance Granular Aluminum Ring Resonators
• Study of Magnetic Field Resilient High Impedance High-Kinetic Inductance Superconducting Resonators
• Synchronizing microwave cQED limit-cycle oscillators
• Switchable spin-photon coupling with hole spins in single-quantum dots