High coherence hybrid superconducting qubit

TL;DR

This paper introduces a new low-impedance flux superconducting qubit with enhanced coherence time, unique potential shape, and dispersive readout, advancing quantum computing hardware design.

Contribution

The paper reports the development and characterization of a novel low-impedance flux qubit with improved coherence and distinctive potential properties.

Findings

Coherence times of approximately 1.5 microseconds for both T2* and T1.

The qubit's potential has a single well due to junction critical current ratios.

Dispersive readout achieved via coupling to a high-Q resonator.

Abstract

We measure the coherence of a new superconducting qubit, the {\em low-impedance flux qubit}, finding $T_2^* \sim T_1 \sim 1.5\mu$s. It is a three-junction flux qubit, but the ratio of junction critical currents is chosen to make the qubit's potential have a single well form. The low impedance of its large shunting capacitance protects it from decoherence. This qubit has a moderate anharmonicity, whose sign is reversed compared with all other popular qubit designs. The qubit is capacitively coupled to a high-Q resonator in a $\lambda/2$ configuration, which permits the qubit's state to be read out dispersively.