Pure kinetic inductance coupling for cQED with flux qubits

TL;DR

This paper introduces a novel qubit-readout architecture using pure kinetic inductance for flux qubits, enabling independent control of dispersive shifts and achieving high-fidelity readout comparable to traditional methods.

Contribution

The work demonstrates a new kinetic inductance-based coupling method for flux qubits, allowing independent tuning of dispersive shifts and high-fidelity quantum state readout.

Findings

Dispersive shifts from 60 kHz to 2 MHz achieved

Quantum state fidelities of 99.7% and 92.7%

Leakage to non-computational states below 0.1%

Abstract

We demonstrate a qubit-readout architecture where the dispersive coupling is entirely mediated by a kinetic inductance. This allows us to engineer the dispersive shift of the readout resonator independent of the qubit and resonator capacitances. We validate the pure kinetic coupling concept and demonstrate various generalized flux qubit regimes from plasmon to fluxon, with dispersive shifts ranging from 60 kHz to 2 MHz at the half-flux quantum sweet spot. We achieve readout performances comparable to conventional architectures with quantum state preparation fidelities of 99.7 % and 92.7 % for the ground and excited states, respectively, and below 0.1 % leakage to non-computational states.