Coherent Operation of a Gap-tunable Flux Qubit

TL;DR

This paper demonstrates a flux qubit with a tunable gap using a DC-SQUID, enabling real-time control of qubit properties and observing coherent dynamics within a GHz tuning range.

Contribution

Introduces a gap-tunable flux qubit using a DC-SQUID, allowing dynamic control of qubit gap during experiments, which was not previously achievable.

Findings

Achieved several GHz tuning range of the qubit gap.

Observed coherent system dynamics at the degeneracy point.

Validated the behavior with numerical simulations.

Abstract

We replace the Josephson junction defining a three-junction flux qubit's properties with a tunable direct current superconducting quantum interference devices (DC-SQUID) in order to tune the qubit gap during the experiment. We observe different gaps as a function of the external magnetic pre-biasing field and the local magnetic field through the DC-SQUID controlled by high-bandwidth on chip control lines. The persistent current and gap behavior correspond to numerical simulation results. We set the sensitivity of the gap on the control lines during the sample design stage. With a tuning range of several GHz on a qubit dynamics timescale, we observe coherent system dynamics at the degeneracy point.