Surpassing the resistance quantum with a geometric superinductor

TL;DR

This paper demonstrates the design, fabrication, and characterization of geometric superinductors with impedance exceeding the resistance quantum, challenging the notion that superinductors must rely on kinetic inductance, and highlighting their advantages for quantum circuits.

Contribution

It introduces a new approach to superinductor implementation using geometric inductance, achieving high impedance, low loss, and high power handling in planar aluminum coil resonators.

Findings

Impedance up to 30.9 kΩ at 5.6 GHz achieved

Capacitance down to ≤1 fF with low loss

High power handling up to 10^8 intra-cavity photons

Abstract

The superconducting circuit community has recently discovered the promising potential of superinductors. These circuit elements have a characteristic impedance exceeding the resistance quantum $R_\text{Q} \approx 6.45~\text{k}\Omega$ which leads to a suppression of ground state charge fluctuations. Applications include the realization of hardware protected qubits for fault tolerant quantum computing, improved coupling to small dipole moment objects and defining a new quantum metrology standard for the ampere. In this work we refute the widespread notion that superinductors can only be implemented based on kinetic inductance, i.e. using disordered superconductors or Josephson junction arrays. We present modeling, fabrication and characterization of 104 planar aluminum coil resonators with a characteristic impedance up to 30.9 $\text{k}\Omega$ at 5.6 GHz and a capacitance down to $\leq1$ fF, with low-loss and a power handling reaching $10^8$ intra-cavity photons. Geometric superinductors are free of uncontrolled tunneling events and offer high reproducibility, linearity and the ability to couple magnetically - properties that significantly broaden the scope of future quantum circuits.