Readout of superconducting flux qubit state with a Cooper pair box

TL;DR

This paper proposes a robust, non-demolition, single-shot readout method for superconducting flux qubits using a Cooper pair box as a transmon, leveraging non-linear Josephson amplifiers for high-fidelity measurement.

Contribution

It introduces a novel readout scheme combining flux qubits with transmon-based Cooper pair boxes for improved measurement robustness and efficiency.

Findings

Enables quantum non-demolition measurement of flux qubits.

Achieves single-shot readout with high fidelity.

Utilizes non-linear Josephson amplifiers for signal enhancement.

Abstract

We study a readout scheme of superconducting flux qubit state with a Cooper pair box as a transmon. The qubit states consist of the superpositions of two degenerate states where the charge and phase degrees of freedom are entangled. Owing to the robustness of transmon against external fluctuations, our readout scheme enables the quantum non-demolition and single-shot measurement of flux qubit states. The qubit state readout can be performed by using the non-linear Josephson amplifiers after a $\pi/2$-rotation driven by an ac-electric field.