Longitudinal coupling between a Si/SiGe quantum dot and an off-chip TiN resonator

TL;DR

This paper demonstrates a longitudinal coupling between a Si/SiGe quantum dot charge qubit and an off-chip TiN resonator, using an adiabatic drive to confirm switchable coupling while maintaining the qubit in its ground state, opening new avenues for qubit control.

Contribution

It provides the first experimental evidence of switchable longitudinal coupling in a solid-state qubit system using a flip-chip design and adiabatic driving techniques.

Findings

Confirmed longitudinal coupling via adiabatic drive

Coupling strength is proportional to drive amplitude

Coupling remains switchable and does not excite the qubit

Abstract

Superconducting cavities have emerged as a key tool for measuring the spin states of quantum dots. So far however, few experiments have explored longitudinal couplings between dots and cavities, and no solid-state qubit experiments have explicitly probed the "adiabatic" regime, where the Purcell decay is strongly suppressed. Here, we report measurements of a double-quantum-dot charge qubit coupled to a high-impedance resonator via a "flip-chip" design geometry. By applying an adiabatic ac drive to the qubit through two different channels, and studying the effects of qubit energy detuning, interdot tunneling, and driving strength, we are able to unequivocally confirm the presence of a longitudinal coupling between the qubit and cavity, while the qubit remains in its ground state. Since this coupling is proportional to the driving amplitude, and is therefore switchable, it has the potential to become a powerful new tool in qubit experiments.